efficient string matching an aid to bibliographic search

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纹理物体缺陷的视觉检测算法研究--优秀毕业论文

纹理物体缺陷的视觉检测算法研究--优秀毕业论文

摘 要
在竞争激烈的工业自动化生产过程中,机器视觉对产品质量的把关起着举足 轻重的作用,机器视觉在缺陷检测技术方面的应用也逐渐普遍起来。与常规的检 测技术相比,自动化的视觉检测系统更加经济、快捷、高效与 安全。纹理物体在 工业生产中广泛存在,像用于半导体装配和封装底板和发光二极管,现代 化电子 系统中的印制电路板,以及纺织行业中的布匹和织物等都可认为是含有纹理特征 的物体。本论文主要致力于纹理物体的缺陷检测技术研究,为纹理物体的自动化 检测提供高效而可靠的检测算法。 纹理是描述图像内容的重要特征,纹理分析也已经被成功的应用与纹理分割 和纹理分类当中。本研究提出了一种基于纹理分析技术和参考比较方式的缺陷检 测算法。这种算法能容忍物体变形引起的图像配准误差,对纹理的影响也具有鲁 棒性。本算法旨在为检测出的缺陷区域提供丰富而重要的物理意义,如缺陷区域 的大小、形状、亮度对比度及空间分布等。同时,在参考图像可行的情况下,本 算法可用于同质纹理物体和非同质纹理物体的检测,对非纹理物体 的检测也可取 得不错的效果。 在整个检测过程中,我们采用了可调控金字塔的纹理分析和重构技术。与传 统的小波纹理分析技术不同,我们在小波域中加入处理物体变形和纹理影响的容 忍度控制算法,来实现容忍物体变形和对纹理影响鲁棒的目的。最后可调控金字 塔的重构保证了缺陷区域物理意义恢复的准确性。实验阶段,我们检测了一系列 具有实际应用价值的图像。实验结果表明 本文提出的纹理物体缺陷检测算法具有 高效性和易于实现性。 关键字: 缺陷检测;纹理;物体变形;可调控金字塔;重构
Keywords: defect detection, texture, object distortion, steerable pyramid, reconstruction
II

longest prefix suffix matching

longest prefix suffix matching

longest prefix suffix matching "Longest Prefix-Suffix Matching: Uncovering the Hidden Similarities"Introduction:In the realm of computer science, algorithms play a crucial role in solving complex problems efficiently. One such algorithm that has garnered attention is the longest prefix-suffix matching algorithm. This algorithm aims to find the longest matching prefix and suffix in a given string, helping in various applications such as pattern matching, text compression, and bioinformatics. In this article, we will delve deep into this algorithm, exploring its intricacies and understanding its applications.1. Understanding Prefix and Suffix:To comprehend the longest prefix-suffix matching algorithm, we must first understand the basic concepts of prefix and suffix. In a string, a prefix is a sequence of characters that appear at the beginning, whereas a suffix is a sequence of characters that occur at the end. For example, in the string "computer," the prefixes are "c," "co," "com," etc., while the suffixes are "r," "er," and "ter."2. Defining the Problem:The longest prefix-suffix matching algorithm addresses the problem of finding the longest common substring that appears both at the beginning and the end of a string, effectively combining the concept of prefix and suffix. For instance, in the string "abcabcxyz," the longest prefix-suffix is "abc."3. Naive Approach:A simple, yet inefficient way to solve this problem is by using a naive approach. We can iterate through all possible substrings, starting from the longest and gradually decreasing their length. For each substring, we can check if it appears both at the beginning and the end of the string. This approach has a time complexity of O(n^2), making it unsuitable for large strings.4. The KMP Algorithm:To overcome the drawbacks of the naive approach, the Knuth–Morris–Pratt (KMP) algorithm offers an efficient solution. The KMP algorithm utilizes a pre-processing step to build an auxiliary array, known as the Longest Proper Prefix (LPP) array, used during the pattern matching phase. This array stores the longest proper prefix that is also a suffix for each substring encountered.5. Building the LPP Array:The construction of the LPP array involves traversing the string and comparing characters to determine the length of the longest proper prefix that is also a suffix. By exploiting previously calculated values, the KMP algorithm minimizes unnecessary comparisons, significantly improving the time complexity to O(n).6. Matching Prefix and Suffix:Once the LPP array is constructed, it can be used to efficiently match the prefixes and suffixes of the string. By comparing the LPP values at each position, we can identify the longest matching prefix and suffix. This breakthrough allows for various applications such as string compression, text indexing, and DNA sequence analysis.7. Applications in Pattern Matching:Pattern matching is a common application for the longestprefix-suffix matching algorithm. By identifying the longest matching prefix and suffix, we can efficiently locate occurrences of a specific pattern within a large string. This application proves invaluable in search engines, text editors, and data mining applications.8. Applications in Text Compression:Text compression techniques, such as Lempel-Ziv-Welch (LZW), utilize the longest prefix-suffix matching algorithm to achieve optimal compression ratios. By finding the longest matching prefix and suffix, redundant information can be eliminated, leading to efficient storage and transmission of textual data.9. Applications in Bioinformatics:In the evolving field of bioinformatics, DNA sequence analysis often requires identifying hidden patterns within genetic data. The longest prefix-suffix matching algorithm aids in recognizing recurring motifs, revealing essential insights into genetic evolution, disease diagnosis, and drug discovery.Conclusion:The longest prefix-suffix matching algorithm unveils the hidden similarities between prefixes and suffixes in a given string. From its humble beginnings to its diverse applications in pattern matching, text compression, and bioinformatics, this algorithm continues to play a pivotal role in various domains of computer science. Throughthe understanding and utilization of this algorithm, we can unlock efficient solutions to complex problems, advancing our technological capabilities.。

Deterministic Finite Automata

Deterministic Finite Automata
/***********************************************
Title : StateMachine-NFA-DFA.c
Author :
Time :
************************************************/
/*********************************************************************************
**
** May 2002 : Marc Norton 1st Version
** June 2002 : Modified interface for SNORT, added case support
** Aug 2002 : Cleaned up comments, and removed dead code.
** and some implementation ideas from 'Practical Algorithms in C'
**
** Notes:
** 1) This version uses about 1024 bytes per pattern character - heavy on the memory.
#ifdef DEBUG_AC
static int max_memory = 0;
#endif
/*==========================function implementation==========================*/
/*----------------MALLOC--------------------*/

USB CPI CLIP 用户手册说明书

USB CPI CLIP 用户手册说明书

USB CPI CLIP User ManualHA031522/1May 2013© 2013 Eurotherm LimitedAll rights are strictly reserved. No part of this document may be reproduced, modified, or transmitted in any form by any means, nor may it be stored in a retrieval system other than for the purpose to act as an aid in operating the equipment to which the document relates, without the prior, written permission of Eurotherm Limited.- - - - - - - - - - - - -Eurotherm Limited pursues a policy of continuous development and product improvement. The specification in this document may therefore be changed without notice. The information in this document is given in good faith, but is intended for guidance only. Eurotherm Limited will accept no responsibility for any losses arising from errors in this document.USB CPI Clip User ManualUSB CPI ClipUser Manual Part Number HA031522 Issue 1 May -2013Contents 1.DESCRIPTION (2)1.1Hardware Features (2)1.2Installation (3)1.3Virtual Comm Port (VCP) Driver (3)2.VCP DRIVER INSTALLATION UNDER WINDOWS XP (4)2.1To install the VCP driver under Windows XP (4)2.2To View the Ports Allocated (6)3.VCP DRIVER INSTALLATION UNDER WINDOWS 7 X32/X64 (7)4.UNINSTALLING VCP DRIVERS (8)ING THE USB CLIP TO CONFIGURE AN INSTRUMENT (9)ING THE USB CLIP TO UPGRADE AN INSTRUMENT (10)6.1To Install the Upgrade Software (10)6.2Launch the Upgrade (12)7.CERTIFICATIONS, ENVIRONMENTAL AND SAFETY (13)Part No HA031522 Issue 1.0 May -13 CN29289 1USB CPI Clip User ManualPart No HA031522 Issue 1.0 May -13 2 1. DescriptionThe CPI clip allows configuration and back up of Eurotherm 3000, piccolo and nanodac series of panel mounted instruments and mini8 rack mounted controller. It supplies power to the instrument derived from the USB port of the host computer so that it can be used without the need for a power connection.external power.than that provided by the USB port.1.1 Hardware FeaturesUsb ConnectionPin FunctionsFunction 1 Vbus Power2 D- Data -3 D+ Data +4 Gnd GroundInstrument connectionThe cable connects to the instrument by a 5 pin configuration clip with a custom plastic insert and a shell. The pin description is shown below,1. instrument.2. from product micro)3. UART receive)4. Ground power connection.5. Provides +5V power to theinstrument.USB CPI Clip User Manual Part No HA031522 Issue 1.0 May -13 3 1.2 InstallationWith reference to the picture:1. The connector can be inserted independently of the device being fitted into its sleeve or not.2. If the controller/indicator is fitted in a panel, remove it and position it on the bench.3. Connect the 5-pin connector to the socket on the side of the device. Push the connector in to the stop.4. Connect the USB connector to the pc which is to be used to install the program.5. After programming one device it is enough to remove the 5-pin connector and insert it directly into theside of a further device and download the configuration data.1.3 Virtual Comm Port (VCP) DriverThe VCP driver emulates a standard PC serial port such that communications can be made with the USB device as a standard RS232 port. Before the CPI clip can be used, therefore, it is necessary to download the VCP driver. If the operating system on the PC is Windows7 the driver should be recognised when the clip is first connected. In this case it should not be necessary to take any further action.If the driver is not installed automatically or if the operating system is XP, for example, it is necessary to install the driver manually, see following sections. The driver can be found on the iTools CD or it can be downloaded from /usbcpi .During the installation the port is allocated a port number. Toinspect the port number after installation go to Ports in the DeviceManager, for example, Control Panel t System t Hardware tDevice Manager t Ports.It is possible to re-number the port - double click on ‘USB Serial Port(COMX)’ to open its properties. In Port Settings t Advanced, theport number can be changed using the drop down box. This mayonly be required in the unlikely event that a port number greaterthan 16 has been allocated since iTools defaults to 16 ports.Although it is possible to increase this to 32 in iTools the scan willbecome slow. It is, therefore, not recommended to make thischange.USB CPI Clip User ManualPart No HA031522 Issue 1.0 May -13 4 2. VCP Driver Installation under Windows XPIf a device of the same type has been installed on your machine before, and the drivers that are about to be installed are different from those installed already, the original drivers need to be uninstalled. Please refer to the Uninstalling VCP Drivers section of this document for further details of this procedure.2.1 To install the VCP driver under Windows XPDownload the latest available VCP drivers from the iTools CD or from /usbcpi . and unzip them to a location on your PC.• Connect the device to a spare USB port on your PC. Windows FoundNew Hardware Wizard will launch andthe screen shown in Figure 2-1 isdisplayed. Select "No, not this time"from the options available and thenclick "Next" to proceed with theinstallation.Figure 2-1• Select "Install from a list or specific location (Advanced)" as shown inFigure 2-2 and then click "Next".Figure 2-2USB CPI Clip User Manual Part No HA031522 Issue 1.0 May -13 5 • Select "Search for the best driver in these locations" and enter the filepath in the combo-box (for example,"C:\CDM 2.02.04" in Figure 2-3) orbrowse to it by clicking the browsebutton. Once the file path has beenentered in the box, click next toproceed.Figure 2-3• If Windows XP is configured to warn when unsigned (non-WHQL certified) drivers are about to beinstalled, the message dialogue shown in Figure 2-4will be displayed. Click on "Continue Anyway" tocontinue with the installation. If Windows XP isconfigured to ignore file signature warnings, nomessage will appear.Figure 2-4• The screen shown in Figure 2-5 will be displayed as Windows XP copies therequired driver files.Figure 2-5USB CPI Clip User Manual Part No HA031522 Issue 1.0 May -13 6 • Windows should then display a message indicating that theinstallation was successful (Figure2-6). Click "Finish" to complete theinstallation for the first port of thedevice.Figure 2-6If the device is based on the FT2232, the Found New Hardware Wizard will continue by installing the USB Serial Converter driver for the second port of the FT2232 device. The procedure for installing the second port is identical to that for installing the first port from the first screen of the Found New Hardware Wizard.2.2 To View the Ports Allocated• Open the Device Manager (located in "Control Panel\System" then selectthe "Hardware" tab and click "DeviceManger") and select "View > Devicesby Connection". The device appearsas a "USB Serial Converter" with anadditional COM port with the label"USB Serial Port" (Figure 2-7). If thedevice is based on the FT2232, twoports will be available from acomposite USB device.Figure 2-7• In the case of the FT2232, port A of the FT2232 will be installed as COMXand port B will be installed asCOMX+1 where COMX is the firstavailable COM port number.Figure 2-8USB CPI Clip User Manual Part No HA031522 Issue 1.0 May -13 7 3. VCP Driver Installation under Windows 7 x32/x64Connect the device to a spare USB port on your PC.With Windows 7, drivers should be installed automatically.If no suitable driver is automatically found then the following procedure should be followed.•In the Hardware tab select Device Manager.• In the Device Manager window there will be a device under Other Devices with a yellowwarning symbol to indicate a problem, i.e. nodriver installed. The text next to this devicewill depend on the device attached. In thisexample the device was a TTL232R device.• Right click on the other device (TTL232R in this example) to bring up a menu as shownbelow.• From the displayed menu select ‘Update Driver Software’.• This will launch the ‘Welcome to the Found New Hardware Wizard’ shown in section 2.1.•Repeat the procedure in section 2.1 to install the driver.• Press the Windows ‘Start’ button to bring up the start menu and select “Control Panel”. • From the Control Panel window select SystemUSB CPI Clip User ManualPart No HA031522 Issue 1.0 May -13 8 4. Uninstalling VCP DriversDevices can be removed using the Device Manager by simply right-clicking on the device and selecting "Uninstall". This will delete the associated registry entries for that device only.Under Windows XP, driver files and OEM INF and PNF files must be removed manually or by using a custom application. OEM INF and PNF files are located in the Windows\Inf directory and can be identified by searching for a VID and PID string matching the device installed e.g. VID_0403&PID_6001. Once the matching OEM INF files are found (e.g. oem10.inf for FTDIBUS.INF and oem11.inf for FTDIPORT.INF), the corresponding PNF files must also be removed (e.g. oem10.pnf and oem11.pnf). Driver files are located in the Windows\System32 and Windows\System32\Drivers directories.Some points to note about this un-installation method:•In the case of FT2232 devices, a composite device is also installed. This can also be removed by clicking on the composite device in the Device Manager and selecting "Uninstall". •If the VCP driver has been installed, the COM port driver should be removed before the bus driver. If the bus is removed first, the COM port will no longer appear in the Device Manager. • If the driver files are deleted while other installed devices still require them those devices will not work correctly. This can be fixed by right clicking the device and selecting "Reinstall Driver" which willreplace the missing files.USB CPI Clip User Manual Part No HA031522 Issue 1.0 May -13 9 5. Using the USB Clip to Configure an InstrumentInstruments are normally configured using iTools. This is a proprietry configuration package available from .• Open iTools and, with the controller connected usingthe clip, press onthe iTools menu bar.•Select ‘Connect via CPI clip or IR cable’ and press OK. • You can also select ‘Scan all device addresses (255 first,etc)’ since controllersconnected with the CPI clip,will be found at address 255regardless of the addressconfigured in the controller.•iTools will search the communications ports andTCPIP connections forrecognisable instruments.• If the instrument is not found, it may be necessaryto enable the port to whichthe clip is configured.•In iTools select Options t Advanced t Show Server.Right click the port andselect Enable.• When an instrument is detected a screen viewsimilar to the one shown willbe displayed.• Press again to stop further scans.•To configure or clone an instrument please refer tothe iTools Help Manual PartNumber HA28838 or therelevant instrument manual.These can be downloadedfrom .USB CPI Clip User ManualPart No HA031522 Issue 1.0 May -13 10 6. Using the USB Clip to Upgrade an InstrumentThe clip can be used to upgrade the firmware in Eurotherm instruments.6.1 To Install the Upgrade SoftwareThe upgrade software may be available through your sales channel.For 3200 series instruments, for example, the upgrade file for the standard controller is ‘3208/3204 Standard Controller Software V2.13’ (V2.13 shows the latest firmware version). Save this to a suitable location.•Run the upgrade software•Press ‘Yes’.•Press ‘Next’. •Select where Setup should place the program’s shortcuts.•Press ‘Next’. •Select where the instrument upgrade should be stored.USB CPI Clip User Manual Part No HA031522 Issue 1.0 May -13 11•Create a desktop icon•Install• FinishUSB CPI Clip User Manual Part No HA031522 Issue 1.0 May -13 12 6.2 Launch the Upgrade• A Read Me text file may be shown. Press ‘OK’ to view the file or ‘Cancel’ to go to theupgrade.•Press ‘Proceed’.•Enter the Port Name as set up by the USB Clip driver. In this example Com5.It is then necessary to follow the procedure in the correct order as described below:-1. Connect the USB plug to the pc.2. Hold down the raise ▲ or lower ▼ button on the instrument and then connect the greenplug to the instrument. Keep the button held down.3. Press ‘Proceed’• The ‘Proceed’ button will temporarily grey as the upgrade software searches for theinstrument.•Press the ‘Proceed’ key when it is enabled to continue with the upgrade and release theinstrument button.• The instrument may now be reconfigured, either using iTools as described in theprevious section or through the user interfaceof the instrument.USB CPI Clip User Manual Part No HA031522 Issue 1.0 May -13 137. Certifications, Environmental and SafetyStorage Temperature-30 to 70 ºC Operating Temperature0 to 55 ºC Relative Humidity5 to 90%, non-condensing Atmospheres Non-corrosive, non-explosiveVibration / ShockEN61131-2 5-150Hz @ 2gApprovals CE Electromagnetic Compatibility EN61326Emissions: Light industrial (Limit B)Immunity: IndustrialRoHS compliance EU; ChinaUSB complianceUSB 1, USB 2 and USB 3 (compatible)USB to serial cable mechanical featuresThe cable has a type A male USB plug at the Personal Computer interface and 5 pin spring pin header at the instrument connection.Weight150g approx Indicator Red LED“Flashing” for data communications Indicator Green LEDUSB connected Overall cable length200cm Cable conductor material CopperUSB CPI Clip User ManualPart No HA031522 Issue 1.0 May -13 14Eurotherm: Internationa©Copyright Invensys Eurotherm Limited 2013Invensys, Eurotherm, the Eurotherm logo, Chessell, EurothermSuite, Mini8, E and Wonderware are trademarks of Invensys plc, its subsidiaries and affiliate owners.All rights are strictly reserved. No part of this document may be reproduced,neither may it be stored in a retrieval system other than for the purpose to acdocument relates, without the prior written permission of Invensys Eurotherm Eurotherm Limited pursues a policy of continuous development and product may therefore be changed without notice. The information in this document Eurotherm Limited will accept no responsibility for any losses arising from erHA031522/1 (CN29289) Contact InformationEurotherm Head OfficeFaraday Close, Durrington, Worthing, West Sussex,BN13 3PLSales EnquiriesT +44 (01903) 695888F ***********General Enquiries T +44 (01903) 268500 F 0845 265982 al sales and supportEycon, Eyris, EPower, EPack nanodac, piccolo, Foxboro,es. All other brands may be trademarks of their respectivemodified or transmitted in any form by any means,ct as an aid in operating the equipment to which the m Limited.t improvement. The specifications in this documentis given in good faith, but is intended for guidance only.rors in this document.USB CPI Worldwide Offices /global Scan for local contactsClip User Manual。

最想要人工智能干什么的英语作文

最想要人工智能干什么的英语作文

最想要人工智能干什么的英语作文全文共3篇示例,供读者参考篇1What I'd Want AI to DoAs a student, I can't help but be fascinated by the potential of artificial intelligence (AI). The rapid advances in this field have already brought about remarkable technologies that assist us in countless ways, from smart assistants that can answer our questions to AI writing tools that help craft essays and papers. However, as amazing as current AI capabilities are, there's still so much more I'd love to see AI do to make my life as a student easier and more productive.One of the biggest challenges I face is staying organized and managing my time effectively. Between classes, assignments, extracurricular activities, and trying to have some semblance of a social life, it can feel like a constant juggling act. That's why I'd love to have an AI assistant dedicated to helping me with time management and organization.Imagine an AI that could not only keep track of all my due dates, appointments, and commitments but also intelligentlyplan out my days and weeks, allocating time for studying, working on projects, attending club meetings, and even scheduling breaks for self-care. It could analyze my workload, priorities, and personal preferences to create customized schedules that optimize my productivity while still leaving room for leisure activities.This AI assistant could also help me stay on top of my tasks by sending reminders and gentle nudges when I need to switch gears or get started on something new. And if I ever fell behind or felt overwhelmed, it could quickly readjust my schedule and provide recommendations for catching up efficiently.Beyond just scheduling, I'd want this AI to be a true organizational powerhouse. It could help me declutter and organize my digital files, notes, and resources, making it easy to find what I need when I need it. It could even analyze my study materials and past assignments to identify areas where I might need extra help or practice, tailoring its recommendations accordingly.Another area where I'd love AI to lend a hand is with research and writing. As a student, I spend countless hours scouring through databases, journals, and online sources to gather information for papers and projects. An AI researchassistant could streamline this process by quickly identifying and compiling relevant sources based on my topic and requirements.But it wouldn't just stop at gathering sources – I'd want this AI to truly understand the content it finds and synthesize the information in a way that makes it easier for me to grasp complex concepts and ideas. It could create concise summaries, visual aids, or even interactive knowledge maps that highlight key points and connections, helping me better understand and retain the material.And when it comes time to start writing, this AI could be an invaluable partner. It could help me outline and structure my thoughts, offer suggestions for improving clarity and flow, and even provide feedback on grammar, style, and overall coherence. Of course, the actual writing and ideas would still be my own, but having an AI to guide and refine my work could be incredibly useful.Moving beyond academics, I'd also love for AI to help me develop important life skills that will serve me well beyond my student篇2What I Most Want AI to DoArtificial Intelligence (AI) is rapidly advancing and transforming various aspects of our lives. As a student navigating the complexities of academia and preparing for the future, I have high hopes for what AI can accomplish. While the possibilities are vast, there are specific areas where I believe AI could make a profound impact and alleviate some of the challenges we face.One of the most pressing issues in the education system is the shortage of qualified teachers in certain subjects and regions. AI-powered virtual tutors and teaching assistants could help bridge this gap by providing personalized instruction and support to students. These AI tutors could adapt to individual learning styles, pace, and knowledge levels, ensuring that no student is left behind. Additionally, they could be available 24/7, allowing students to seek help whenever needed, without being constrained by traditional classroom schedules.Furthermore, AI could revolutionize the way we assess and evaluate student progress. Traditional testing methods often fail to capture the depth of a student's understanding or account for different learning styles. AI-powered adaptive assessments could tailor questions based on a student's responses, providing a more accurate and comprehensive evaluation of their knowledge and skills. This could not only reduce the stress and anxietyassociated with high-stakes testing but also provide educators with valuable insights to improve their teaching methods.Beyond academics, AI could play a significant role in addressing mental health challenges among students. The pressure to excel, coupled with social and personal issues, can take a toll on a student's well-being. AI-powered chatbots or virtual counselors could provide a non-judgmental and confidential space for students to express their concerns and receive guidance. These AI systems could be trained to recognize patterns and warning signs of mental health issues, and provide appropriate resources or interventions.In the realm of career guidance and planning, AI could be a game-changer. Many students struggle with navigating the complex landscape of career options, matching their interests and skills with suitable paths. AI-powered career advisors could analyze a student's academic performance, extracurricular activities, and personality traits to recommend potential careers or educational programs. These AI systems could also provide insights into job market trends, helping students make informed decisions about their future endeavors.Additionally, AI could enhance the accessibility of education for students with disabilities or those in remote areas.AI-powered virtual assistants could transcribe lectures, provide real-time captioning, or even translate content into different languages, ensuring that no student is left behind due to physical or geographical barriers.However, as exciting as these possibilities are, it is crucial to address the ethical considerations and potential risks associated with the integration of AI in education. Privacy and data security must be prioritized to protect students' personal information and prevent misuse. Furthermore, AI systems must be designed and trained with a focus on fairness, avoiding biases that could perpetuate existing inequalities or discriminatory practices.Moreover, while AI can be a powerful tool, it should not be viewed as a replacement for human educators and support systems. The personal connections, empathy, and guidance provided by teachers and counselors are invaluable and cannot be fully replicated by machines. AI should be viewed as a complementary resource,篇3What I Would Most Want an AI to DoAs a student in this rapidly advancing technological age, the potential of artificial intelligence both excites and terrifies me.On one hand, I can envision AI revolutionizing countless facets of our world, making our lives immeasurably easier and more efficient. But I also have grave concerns about AI running amok, superseding human intelligence and agency. If I could have an AI assistant to aid me, there is one main task I would prioritize above all others: being an impartial source of truth and guiding light through the murky waters of misinformation that seem to be flooding society.In this era of social media echo chambers, confirmation bias, and utterly baseless conspiracy theories being peddled as facts, it is becoming increasingly difficult to discern truth from fiction. We are inundated with a relentless deluge of information and misinformation from countless sources, all claiming to be accurate and authentic. As someone who values truth, rationality, and empirical evidence, this tendency towards post-truth narratives is profoundly disturbing to me.What I desperately want is an AI that could cut through the noise, the agendas, and the deception to provide me with clear, dispassionate assessments of what is real and what is not. An AI with an utterly impartial perspective, fueled by the collective knowledge of humanity, that could quickly analyze any claim orpiece of information and render a judgment based solely on established facts, data, and logic.Imagine if you could pose any question or make any statement to an AI, and within seconds receive a detailed report explaining whether that claim is substantiated or merely propaganda or fiction. The AI could scour all available data sources to trace the roots and veracity of that claim. It could analyze authenticating evidence, fact-check details, identify logical fallacies, and detect even the most subtle indicators that the information may be misleading or falsified. With its advanced language processing capabilities, it could decode nuanced rhetorical devices used to sow。

计算机专业英语试题及答案

计算机专业英语试题及答案

计算机专业英语试题及答案1. 选择题1. Which of the following is not a programming language?a) Javab) HTMLc) Pythond) CSS答案: b) HTML2. Which protocol is used for sending and receiving email?a) HTTPSb) FTPc) SMTPd) DNS答案: c) SMTP3. What does the acronym CPU stand for?a) Central Processing Unitb) Computer Processing Unitc) Control Processing Unitd) Central Power Unit答案: a) Central Processing Unit4. Which programming language is commonly used for web development?a) C++b) Javac) JavaScriptd) Swift答案: c) JavaScript5. What does HTML stand for?a) Hyperlinks and Text Markup Languageb) Hyper Text Markup Languagec) Home Tool Markup Languaged) Hyper Text Modeling Language答案: b) Hyper Text Markup Language2. 填空题1. The process of converting high-level programming code into machine code is called ___________.答案: compilation2. HTTP stands for ___________ Transfer Protocol.答案: Hyper Text3. The process of testing software by executing it is called ___________.答案: debugging4. Java is an object-_____________ programming language.答案: oriented5. DNS stands for Domain Name ___________.答案: System3. 简答题1. What is the difference between TCP and UDP?答案: TCP (Transmission Control Protocol) is a connection-oriented protocol, which means it establishes a connection between the sender and receiver before transferring data. It ensures that all packets are received in the correct order and provides error checking. UDP (User Datagram Protocol), on the other hand, is a connectionless protocol that does not establish a direct connection before transmitting data. It does not guarantee packet delivery or order but is faster and more efficient for time-sensitive applications.2. What is the purpose of an operating system?答案: An operating system (OS) is a software that manages computer hardware and software resources and provides common services forcomputer programs. Its primary purpose is to enable the user to interact with the computer and provide a platform for running applications. It manages memory, file systems, input/output devices, and multitasking. The OS also handles system security and resource allocation to ensure optimal performance.4. 解答题请参考下文并给出自己的解答。

DSP处理器上的高效串匹配实现

DSP处理器上的高效串匹配实现

2021年4月第4期Vol. 42 No. 4 2021小型微型计算机系统Journal of Chinese Computer SystemsDSP 处理器上的高效串匹配实现叶鸿',顾乃杰J 林传文$'(中国科学技术大学计算机科学与技术学院,合肥230027)2 (合肥学院计算机科学与技术系,合肥230601)E-mail : yehong91 @ mail . ustc. edu. cn摘 要:字符串匹配是生物识别、入侵检测的基础,也是大数据互联网时代的研究热点.随着现代信息技术的发展,日常工作生 活中移动及手持小型化设备的使用越发普遍.这些设备的应用场景中包含大量有关串匹配的需求,如人脸识别、实时数据查询等.串匹配算法的实时和准确性决定了使用场景的范围,因此在DSP 处理器等移动小型化设备的嵌入式处理器上实现高效串 匹配算法的问题变得十分迫切.该文针对DSP 处理器因缺乏逻辑判断与跳转指令,难以支持高效串匹配运算的问题,提出了一种基于DSP 平台特点的改进串匹配算法.该算法釆用位并行的思路,在DSP 处理器上实现了串匹配算法的并行化.同时通过前 序启动、基于VLIW 的数学运算替代逻辑判断.Q-grams 等优化手段,提高该算法对于DSP 平台的适应性与执行效率,最终实现 了一种基于HXDSP 的高效串匹配算法VBNDM2.实验结果表明,本算法针对DSP 平台,有效地提高了串匹配的效率,实现了 算法的高效并行化.关 键词:DSP ;串匹配;VLIW ;SIMD ;位并行中图分类号:TP18 文献标识码:A 文章编 号:1000-1220(2021 )04-0847-06Efficient String Matching Algorithm for DSP ProcessorYE Hong 1 ,GU Nai-jie 1 ,LIN Chuan-wen 21 (School of Computer Science and Technology , University of Science and Technology of China , Hefei 230027, China )2 ( Department of Computer Science and Technology , Hefei University , Hefei 230601 , China )Abstract : String matching is the basis of biometrics and intrusion detection , and it is also a research hotspot in the era of big data Inter ­net. With the development of modem information technology , the use of mobile and handheld miniaturized devices in daily work and life is becoming more common. The application scenarios of these devices include a large number of requirements related to string matching , such as face recognition and real-time data query. The real-time and accuracy of the string matching algorithm determinesthe range of use scenarios , so the problem of implementing an efficient string matching algorithm on an embedded processor of a mo ­bile miniaturized device such as a DSP processor becomes very urgent. Aiming at the problem that DSP processors lack support for ef ­ficient string matching operations due to lack of logical judgment and jump instructions , this paper proposes an improved string matc ­hing algorithm based on the characteristics of the DSP platform. This algorithm adopts the idea of bit parallelism , and realizes the par ­allelization of the string matching algorithm on the DSP processor. At the same time , through the pre-launch , VLIW-based mathemati ­cal operations instead of logical judgments ,Q-grams and other optimization methods ,the algorithm's adaptability and execution effi ­ciency for the DSP platform are improved. Finally , an efficient string matching algorithm VBNDM2 based on HXDSP is implemented.Experimental results show that this algorithm is aimed at the DSP platform , which effectively improves the efficiency of string matc ・hing and achieves efficient parallelization of the algorithm.Key words : DSP ; string matching ; VLIW ; SIMD ; bit parallel1引言串匹配,是一种在已给定的字符、符号序列(文本串)中查找某一特定字符、符号序列(模式串)所有出现情况的算法.它广泛应用于语音分析与识别,信息检索,生物检测等方 向,是计算机领域研究的基础问题之一⑴.随着移动互联与 计算生物学的高速发展,信息査找、入侵检测、基因检索等涉及串匹配问题的应用对移动便携和功耗的要求越来越高,单一 PC 平台已经很难满足不同应用场景对性能的专业需求, 移动化及手持小型化设备受到越来越多的关注⑵.如何针对这些设备选取合适的处理芯片,并高效的实现串匹配算法,是 当下研究的重点[3'41.DSP 处理器,兼具低功耗、高性能、易编程等特点,在信号及图像处理领域有着的天然优势,也因此在移动设备及小型收稿日期:2020-04-08收修改稿日期;2020-05-25基金项目:安徽省科技重大专项项目(180****1011)资助;合肥学院科研发展基金项目 (19ZR03ZDA )资助.作者简介:叶 鸿,男,1991年生.博士研究生,研究方向为体系架构优化与并行计算;顾乃杰,男,1961年生.博士,教授, 博士生导师,CCF 会员,研究方向为并行计算、并行处理和并行体系结构等;林传文,男,1986年生,博士,讲师,研究方向为体系架构优化、深度 学习.848小型微型计算机系统2021年设备处理中受到越来越多的关注.高性能DSP处理器不仅拥有强大的计算能力,还支持单指令多数据流(SIMD)、超长指令字(VLIW)等硬件技术,这使得串匹配并行化在DSP处理器上有着广阔的研究空间和使用价值•将复杂算法应用于DSP处理器并与通用处理器协同工作进行特征提取,当复杂的算法在DSP处理器上运行时,通用处理器可以专注于图像采集、用户界面和外围控制,这为移动设备的性能保证和场景推广提供了无限可能,在生物识别、移动检测等领域,有着重要的意义⑸.与此同时,在串匹配领域有很多优秀的算法可以进行高效匹配工作,算法逻辑思路也各不相同,但不可避免都会涉及大量不确定的判断与跳转.而基于哈弗体系架构的DSP处理器,非常擅长数据密集的高性能运算.但频繁的判断跳转,会带来流水线的停滞,预取指令槽的反复装入与排空,这会显著影响DSP处理器的运算效率.如何合理规避跳转,发挥处理器的运算能力,是实现高效串匹配算法的关键问题"列.针对上述问题,该文提出了一种基于DSP处理器的改高效串匹配算法.这一算法采用位并行的思路,同时通过多种优化手段,提高该算法对于DSP平台的适应性与执行效率,最终实现了一种针对HXDSP的高效串匹配算法VBNDM2 (VectorizationBackward Nondeterministic Dawg Matching in2・Grams).2背景介绍串匹配算法在信息检索和信息分析相关的众多领域都有着众多应用.自1970年S.S.Cook从理论上证明单模式匹配问题可以在O(m+n)时间内解决以来,科学界已提出120种以上的字符串匹配算法⑼.其中有50多种是在近10年内提出的,但真正实用且被广泛应用于各实践场景的寥寥.这是因为基于串匹配问题的研究存在着理论与实践间脱节的问题.目前,针对串匹配问题的研究主要分为两个方向,一是改进现有算法以适应目前超大数据量及高速网络环境;另一个是将现有算法应用到不同硬件环境上,并针对特定硬件结构特点来优化提高串匹配效率[10J11.2.1串匹配算法分析由于各种模式的匹配算法都是由单模式串匹配算法拓展而来,单模式匹配是文本、符号处理等领域研究应用的基本组件.而为了获得针对单模式串匹配的确切匹配位置,精确单模式匹配也因此成为串匹配问题的核心和基础.所谓精确单模式匹配(Exact single pattern string matching),指的是对于给定字符集S(ISI=a),2*为字符集2的一个Kleene闭包(下文简称闭包),给定文本串T=r o t1-t….)和模式串P=p o p l-P”-i,其中T,Pe.从而求解集合:O=|pos\P\_j}=T\_pos +J],fr>r\/0^j<m,0WposWn-m]的问题.传统串匹配算法中的单模式匹配,依照其搜索方式的特点可分为:前缀搜索方式、后缀搜索方式和子串搜索方式.前缀搜索方式的主要代表算法主要为KMP®〕算法,Shift-And 算法和Shift-Or算法问等.前缀搜索的特点是采用自前向后的顺序判断模式与匹配串的对比情况,然后凭借已匹配成功的数据计算后续可后移的最大位数.而后缀搜索方式算法主要有BM算法E、Horspool算法和Sunday算法购等.后缀搜索方式算法的思路与前缀相反,它在检索时采用从后向前的方式,首先从文本串的最后字符开始检索.基于后缀方式算法的优势在于检索匹配失败后可以获得一个较大的跳跃位数.最后,子串搜索则是基于自动机的执行方式,它的代表算法有BDM算法⑴、BNDM丽算法和B0M算法和它的延伸算法等.2.2基于比特位并行的串匹配算法在充分利用设备存储器的字长且兼顾操作的内在并行性的条件下,基于位并行的串匹配算法是目前速度最快、效率最高的串匹配算法.但与此同时,基于位并行算法的效率也会受到实际串长度的限制.若模式串的实际长度不大于平台的机器字长时,可执行高效位并行匹配;反之,若模式串长度大于甚至远大于机器实际字长时,算法中字符拼接产生的损耗则会显著降低位并行算法的效率〔切.位并行算法,指的是将多个值打包,存放在一个指定计算机字长空间中,并在每次匹配操作后自动更新所有比对值的技术.这一算法旨在将多个匹配值贮存在计算机的单字空间里,形成检索表.并采用简单的运算操作(例如位操作)更新和持续维护它们,如与操作(AND)、或操作(OR)和加法操作(ADD).而在实际过程中,最普遍的方法是对给定的模式串和匹配串生成一个二维数组用以暂存字符串中所有字符中的匹配与不匹配信息.位并行算法可以将判断和处理压缩在位运算部分而减少判断,因此也更适合DSP处理器使用.常见的位并行串匹配算法有Shift-Or、Shift-And、BNDM等.其中,BNDM算法相对于Shift-Or、Shift-And算法有着较少的判断跳转和更好的平台适应性.基于BNDM算法,又有SBNDM、BNDM2等延伸算法12°]2.3BDM与BNDM算法介绍BDM(Backward DAWG Matching)算法口,是一种最早的子串跳跃型的串匹配算法.它主要基于后缀自动机的特点检索并识别所包含的所有子串.这一算法采用Trie有根树来执行有限状态自动机,自右向左倒序检索匹配窗,进而识别出匹配串中能够于子串部分相匹配的最长相同字符序列n.而当时间序列长度I n I大于等于实际窗口长度m时,执行判定匹配串与检索当前位置是否相同,相同则反回实际检索位置;若不同则代表着检索序列部分匹配,则匹配指针右移m-n个字符,继续执行匹配算.虽然BDM算法的理论最坏时间复杂度为0(mn),但它是第一个实现平均时间复杂度O(nlog”(…/巾))的算法,这对后续的检索算法的发展,有着重要的理论研究意义.BNDM算法问也是一种可以达到0(nlog”(n/m))平均时间复杂度的算法,它的本质是BDM算法的位并行实现,且曾经是世界上效率最高,也最有实际应用价值的串匹配算法之一.时至今日,BNDM算法已成为一类专门的串模式匹配算法,在嵌入式串匹配领域有着重要的影响力.这一算法的理论基础是位并行的实现了一种不确定因子自动机的仿真过程,它模拟了一个不确定因子自动机所有前缀的识别过程.算法首先的预处理阶段构建了一个向量表B,这一形式类似于Shift-And算法的数据表,并通过在文本上滑动长为m的检索4期叶鸿等:DSP处理器上的高效串匹配实现849窗为来实现实际检索逻辑.其实际执行过程中会先对齐检索窗,并采用向后检索的方式扫描窗口同时相应更新自动配置.而当算法检索到一个P的后缀(即P的前缀)并设置D和B[C]的第m位时,算法记录实际窗口位置.而当D变为零(即找不到P的进一步前缀)或算法执行了m次迭代(即找到匹配)后,尝试结束并移动窗口至可识别的、最长适当前缀的起始位置.BNDM算法的空间和时间复杂度分别为O(&「m/ w])与0(f m2/w~\).3基于DSP处理器的串匹配优化方法基于串匹配的算法研究,首要任务即是处理串匹配的等概率模型.等概率模型问题,是指针对确定的模式串和文本串,各字符元素出现的概率互相独立,并且各自相同的体系模型.自上世纪70年代姚期智证明在等概率模型的条件下,精确单模式字符串匹配的最差、最优以及最优平均时间复杂度分别为O(n)、O(n/m)、O(Mog”(n/m))以来,各时间复杂度已被相应算法证实0〕.然而在实际应用场景中,文本串与模式串普遍会满足某些特定的概率分布,这使得实际匹配算法只能接近而很难达到最优或最差的时间复杂度.因此,当样本数据量足够大、模式串足够长的时候,平均时间复杂度对串匹配的最终性能影响最大8】.而提高串匹配的方法,主要有结合硬件结构、减少循环次数、缩短循环体、提高跳跃距离等. 3.1DSP下串匹配的特点与通用PC处理器相比,基于SIMD和VLIW架构的DSP平台有着更低的功耗和更高专业运算效率的特点.SIMD 架构的分簇特点,可以通过一条指令使相同算法在多个分簇运算单元(FU)上同时运算.但不同于单纯的线程并行,SIMD 架构需要在不同FU上同一时刻进行相同的操作,这也因此对并行运算的判断流程提出更高要求.对于特定情形如并行执行时部分分簇需要进行跳转,而剩余部分不需跳转的问题,需要详尽、严密的判定逻辑.与此同时,DSP处理器的VLIW 架构,可将多条指令整合在同一发射槽中同步执行.这使得DSP处理器对于算法中部分指令执行顺序并非那么敏感,甚至可采用部分以空间换时间的策略,额外增加同一指令发射槽中的指令数量,以解决部分逻辑跳转问题.最后,对在处理器执行过程中,数据在完成访存写入后再次读出,需要间隔相应的时钟周期.因此,为保证流水线执行更加高效,适当进行循环展开与指令改写,对算法效率提升有很大帮助.3.2Q-grams与提高最大跳跃距离DSP处理器普遍采用哈佛架构(Harvard),它的主要特点是数据和程序段存储在不同的空间中,可以分别独立编码和寻址.这使得DSP处理器有着高效的访存模式,但在逻辑判断方面,并不具有优势.HXDSP平台包含两组分支预测流水线,但因为串匹配算法匹配跳转执行步长普遍较短,往往难以满足分支预取的指令执行需求.因此若预测成功,顺序执行效率较高;若预测分支失败,处理器则需排空流水线,重新预取、并载人未来所执行的指令.由于这一指令流转的过程会产生大量的额外时钟开销,为减少分支跳转中排空流水线过程所产生的时钟开销,应当尽量减少分支跳转的频度•而在当代高效串匹配算法的实现中,可采用Q-grams的思想来解决上述问题.即采用同时读入多个字符的形式,将这些字符作为整体进行检索和匹配.通过整体查找的方式,降低查找频次,提高准确度,从而提高效率.最早提出将多个字符同时读入字符串的人是K. Fredriksson^,他发现在实际模式匹配如英文语料、基因查询等检索过程中,实际匹配成功的概率远小于产生非匹配状态并跳转的概率.因此.Q-grams结构的核心思想即是更快地迭代搜索过程,继续提高非匹配的概率,并跳过它•Q-grams策略在检索匹配状态时,不同于传统串匹配的逐字比较,它可以同时读入连续的q个字符.基于这一策略,当进行中的匹配当前位置没有Q个字符连续组合时,会立即跳过,这使得指令流更加简单,检索更加快捷,看似为跳转增加了负担.但也因为实际循环体因此被尽可能的缩短,算法因此可以更高效地推进及跳跃(这一跳跃距离通常为+1)•其实际匹配结构为:«1)&-«(g-l))不同于BNDM算法采用Last变量来存储和标记找到的前缀位置,Q-grams策略采用变量i(一般指向的位置)来直接更新跳转位置,这令循环更加简洁同时也使得算法更加高效.与此同时,单纯的Q-grams策略同样存在不足,由于q-grams没有采用变量存储最后一个所找到的前缀,而是通过变量i指向P”g的计数器位置的方式直接更新结构.其实际策略即将普通单字节的字符集,组合成连续多字节的大规模字符集.故基于Q-grams策略的算法相对于传统单字结构占用更多的存储空间,这同时会带来Cache命中问题.此外,不同平台系统对于Q-grams策略串匹配算法的硬件支持程度的不同,也决定了<7值本身并非越大越好,连续的读取会涉及数据对齐问题.Kalsi等人的测试表明皿[,相对于对齐读取,未经对齐的内存读取在x86平台上的速度损失可以达到70%.而大量数据因读取的未对齐,其本身连续访问或跳转执行效率也受到严重影响,这对大q值Q-grams算法的执行也产生了制约.而在传统DSP平台上,硬件大多支持双字读写,并为双字处理提供了大量灵活指令与操作,这使得DSP处理器上两个相邻寄存器的数据既可以组成一个数组进行共同运算,也可以灵活地单独运算•这一结构为2-grams策略提供了稳定而高效的硬件支持.3.3提高前序启动与判断过程以数理逻辑的角度分析串匹配算法,为提高其性能效率,势必要缩短循环体,减少循环次数,增大跳跃距离.而基于缩短循环体的角度提高检索效率,则可对模式匹配的检索首部进行处理.其代表性算法如Shift-Or或BNDM等基于位并行的算法,它们通过构建辅助向量表B,利用比特位掩码序列D 去进行匹配运算,检索不匹配则立即跳转.这一策略体现在实际算法执行过程中时,首先考虑将比特位掩码序列P起始置零,并按照既定规则,移位并进行逻辑操作.假设即将进行的匹配模式串最后一位T[p OS]=M,由于该掩码序列初始值为全0,进行第一次移位操作读入的模式串字符后,掩码序列D=B[M].在这一操作过程中,算法需在循环体末将掩码序列D置零,并在下一次循环首部与模式串序列进行逻辑运算.这样的操作显然存在冗余和重复,850小型微型计算机系统2021年可二者合一缩小循环体.同时,如果将这一整合操作提前至循环首部,并作为单独循环,若检索前端便匹配失败,即可快速进行跳转跃迁,以提高检索速度.上述优化策略的核心思想是跳过检测中的最长前缀部分,将循环更多地压缩在前序过程中,使得内层算法变得更加简洁.因此这一策略虽然增加了循环数量,但实际减少了平均移动长度,可带来实际执行过程中的算法性能提升.3.4通过VLIW结构将逻辑判断转为数学运算基于VLIW与SIMD的DSP处理器,相对于传统的PC 平台,其指令跳转与分支预测是处理器的弱项•尤其是在基于并行处理的串匹配应用过程中,由于指令并行并非线程并行,对于不同的分簇及运算单元,在同一指令下,必须完成同样的工作.但在实际应用场景中,串匹配的过程是不确定的,并行执行的判断过程,跳转也有先后•这就导致了在分支跳转的过程中,往往会出现部分分簇需要跳转,而部分分簇又顺序执行的情况•由于DSP的硬件架构无法处理这样的跳转问题,流水线也会因此紊乱.这一问题,是限制DSP处理器的串匹配算法高效执行的最重要问题之一.在并行执行串匹配算法时,实际上同一指令发射槽,需要执行的指令数较少.此时可选择横向并行再执行一组甚至多组串匹配算法,但在这一环境下,判断跳转变得更加复杂.进行代码级的跳转分类,无疑增加了算法的复杂性,且无法带来实际意义的性能提升.另一种思路是,将判断比较等算法通过逻辑与、或的方式融入流水线执行过程中.并采用扩大、复杂算法的方式,以类似“空间换时间”的策略,将部分跳转取代为逻辑、数学运算.考虑到超长指令字架构下同一指令发射的指令槽使用较为空闲,这一思路,有较强的可执行性.在通用的BNDM算法中的while循环体内,包含另-while循环体.可以看出,串匹配算法在代码执行时由于大量循环、判断、跳转,会长期处于流水线预取装载的过程中,而对运算部件的需求量较小.DSP芯片庞大且高效的数学运算部件,在大多数时间都是闲置的.对于DSP芯片的分支预取结构,在完成代码执行后,流水线会分别装入跳转与顺序执行两种情况的未来指令•而执行完循环后,又需要重新进行流水线的排空和装入,造成流水线的停滞,从而降低检索速度.如算法1所示,改写后的算法将外层循环提出、展开后并入内层循环,可将双层循环算法整合成一个单循环算法.从传统算法优化的角度,外层循环的部分代码额外执行了很多次,对于算法性能提升是起反作用的.但在基于VLIW结构的HXDSP上,图中所有额外操作,可以并行在指令行的其他发射槽中执行,并未增加额外时钟开销.如LAST&&True等操作,可以在循环体内提前计算与准备,最终更新其参数值时,依然只需要一个时钟周期的运算.通过VLIW结构将逻辑判断转为数学运算,这是一种利用空间换时间的算法优化思路.将判断跳转用额外的数学运算代替,可以减少指令的分支预取与跳转可能.对于串匹配算法这种不适合多路并行,指令发射槽和运算部件使用率较低的算法应用,有着显著的性能提升效果.4实现平台介绍该文算法的具体实现平台为HXDSP处理器.HXDSP是国内某研究所研制的第2代高性能超长指令字(VLIW)DSP 芯片,其结构如图1所示.它是一款32位静态超标量处理器,内部集成2个新一代处理器核eC104+,工作主频为800MHz~1GHz.采用16纳米工艺,16发射、SIMD架构,通信带宽为252Gbps,存储容量105Mbit,运算性能可达134GFLOPS.控制标志寄存器访问单元代码存储器i程序控制流]|译码]地址、顺序控制执行核x芝执行核丫匕乂执行核z)=执行核t=地址产生器u地址产生器vWK数据总线交叉开关数据存储器0数据存储器1数据存储器2数据存储器3数据存储器4数据存储器5VV图1HXDSP104X系统架构Fig.1Architecture of HXDSP104x system HXDSP采用哈佛体系结构,有独立的程序总线和数据总线.HXDSP处理器有宽度为512bit的指令总线和非对称全双工的内部数据总线.它包括4个基本执行宏(element opera­tion macro),每个执行宏由8个算术逻辑单元(ALU)、8个乘法器(MUL)、4个移位器(SHF)、1个超算器(SPU)以及128个通用寄存器组成.5算法实现该文提出一种基于HXDSP的改进算法,其算法伪代码如算法1所示.由于这一算法为基于BNDM算法在HXDSP平台上的向量并行优化算法,包含提前启动、Q-grams(Q值在此取2)、VLIW逻辑转化等优化策略,故简称为VBNDM2算法.HXDSP处理器访存可支持双字读写,同时访问并读取连续的丁加和T”小位数据与单字读取所花费的时钟周期数相同,因此基于双字读写策略,可以有效提高检索的访存效率.而采用G-grams方式的2-grams访存方式读取,既可以充分发挥处理器的硬件特点,又利用了算法的优势,可以有效提升效率.若将参数Q的形式扩大至3、4,在带来额外的硬件开销的同时,因访存形式不同,效率并不高.此外,基于快速启动策略,也并非必须对每个分支都展开循环体进而合成•对前几位进行快速检索,一旦不匹配直接跳转,便能有效减少匹配,提高命中率,这同样也是减少跳转和预取的方式之一.因此最终算法包含双重循环,内层为2个循环.在这样的循环算法中,需要对最后一个J==0的if判断进行优化去除.通过逻辑运算如X=j&\和y=x・i等,即可将if判定转为指令并行.同时对检索的记录过程采用分别记。

算法可以快速完成用户与信息的精准匹配英语作文

算法可以快速完成用户与信息的精准匹配英语作文

算法可以快速完成用户与信息的精准匹配英语作文全文共3篇示例,供读者参考篇1Algorithms: The Digital Matchmakers of the Modern AgeIn today's digital age, we are constantly bombarded with an overwhelming amount of information. From social media feeds to online shopping platforms, the internet has become a vast ocean of data, and navigating through it can be a daunting task. However, thanks to the power of algorithms, we now have the ability to quickly and accurately match users with the information they need, making the online experience more efficient and personalized.As a student, I have experienced firsthand the benefits of algorithmic matching in various aspects of my academic life. Whether it's finding relevant research papers for my assignments or discovering new learning resources tailored to my interests, algorithms have proven to be invaluable tools in enhancing my educational journey.One area where algorithmic matching shines is in online learning platforms. These platforms employ sophisticatedalgorithms that analyze a student's performance, learning style, and interests to recommend personalized content and courses. By presenting material that aligns with a student's strengths and weaknesses, these algorithms can significantly improve the learning experience and increase knowledge retention.For example, when I was struggling with a particular concept in my calculus class, the online learning platform I was using recommended a series of videos and practice problems specifically designed to address my areas of weakness. The algorithm had analyzed my previous performance and identified the topics I needed to focus on, allowing me to efficiently target my weaknesses and improve my understanding of the subject.Another powerful application of algorithmic matching is in the realm of online research. As a student, conducting research is a crucial part of my academic life, and navigating through the vast expanse of scholarly literature can be a daunting task. However, with the help of algorithms, I can quickly find relevant and reliable sources that align with my research interests and requirements.One particularly useful tool is citation recommendation algorithms. These algorithms analyze the content and citations of research papers I have previously accessed and suggestadditional relevant sources based on their similarity to my existing material. This feature has saved me countless hours of manual searching and has allowed me to explore new perspectives and ideas that I might have otherwise missed.Beyond academia, algorithmic matching has also transformed the way we consume entertainment and make purchasing decisions. Streaming platforms like Netflix and Spotify use complex algorithms to analyze our viewing and listening habits, and then recommend content that aligns with our preferences. This personalized approach ensures that we are exposed to new and engaging content that we are likely to enjoy, saving us from the overwhelming task of sifting through countless options.Similarly, e-commerce platforms like Amazon employ algorithmic matching to provide personalized product recommendations based on our browsing and purchase history. These algorithms analyze our past behavior and preferences to suggest items that we may be interested in, streamlining the shopping experience and increasing the likelihood of making satisfactory purchases.While the benefits of algorithmic matching are undeniable, it is important to acknowledge potential concerns and limitations.One major issue is the potential for algorithmic bias, where the algorithms may perpetuate existing societal biases or prioritize certain types of content over others. Additionally, there are privacy concerns surrounding the collection and use of personal data to fuel these algorithms.Despite these challenges, the potential of algorithms to enhance our online experiences and streamline information access is immense. As technology continues to evolve, we can expect to see even more sophisticated and advanced algorithms that can adapt to our changing needs and preferences, further blurring the lines between the digital and physical worlds.In conclusion, algorithms have become the digital matchmakers of the modern age, seamlessly connecting us with the information, entertainment, and products that align with our unique interests and preferences. As a student, I have experienced firsthand the transformative power of algorithmic matching in enhancing my educational journey and streamlining my research process. While there are valid concerns to address, the benefits of these algorithms are undeniable, and their impact on our lives will only continue to grow in the years to come.篇2Algorithms: The Digital Matchmakers of the Modern AgeIn today's world, we are constantly bombarded with a deluge of information from countless sources. From social media updates to online shopping recommendations, targeted advertising to personalized news feeds – it's as if the digital realm has become a colossal matchmaking service, endlessly striving to pair us with the content and connections most aligned with our interests and preferences. At the heart of this intricate matchmaking process lie powerful algorithms – the unseen puppet masters orchestrating the flow of information in our digitally-driven lives.As a student navigating the complexities of the 21st century, I have come to appreciate the pivotal role these algorithms play in streamlining our access to information. Gone are the days of sifting through encyclopedias or endlessly scrolling through pages of irrelevant search results. Today's algorithms possess an almost clairvoyant ability to anticipate our needs and curate the information we seek with astonishing precision.Take, for instance, the realm of online shopping.E-commerce giants like Amazon and Alibaba have harnessed the power of sophisticated algorithms to revolutionize the shopping experience. By analyzing our browsing histories, purchasepatterns, and even geographic locations, these algorithms can predict our preferences with uncanny accuracy. The result? A personalized storefront tailored to our unique tastes, seamlessly guiding us towards products we're likely to appreciate – a true testament to the art of algorithmic matchmaking.But the influence of algorithms extends far beyond the realm of retail therapy. Social media platforms like Facebook, Twitter, and Instagram employ intricate algorithms to curate our news feeds, serving us a carefully curated selection of updates, posts, and advertisements based on our online activities, social connections, and expressed interests. These algorithms act as digital curators, filtering out the noise and presenting us with the content most resonant with our personalities and inclinations.Even in the academic realm, algorithms have become indispensable tools for enhancing our learning experiences. Online educational platforms and digital libraries leverage algorithms to recommend relevant courses, research materials, and supplementary resources based on our academic profiles, previous searches, and demonstrated areas of interest. These algorithmic matchmakers ensure that the vast expanse of knowledge at our fingertips is tailored to our unique educationaljourneys, empowering us to explore and expand our intellectual horizons with unparalleled efficiency.Underpinning these remarkable feats of algorithmic matchmaking are intricate mathematical models and machine learning techniques. By ingesting vast troves of data, these algorithms can discern patterns, correlations, and nuances that would be virtually impossible for the human mind to comprehend. Through a process of continuous learning and refinement, they evolve, adapting their recommendations and output to better align with our ever-changing preferences and behaviors.Yet, as with any powerful technology, the use of algorithms in user-information matching is not without its controversies and ethical considerations. Issues of data privacy, algorithmic bias, and the potential for manipulation have sparked heated debates and regulatory scrutiny. Critics argue that these algorithms can perpetuate societal biases, reinforce echo chambers, and compromise our autonomy by shaping our choices and perspectives in ways we may not even realize.Nonetheless, the potential benefits of algorithmic matchmaking are too significant to ignore. In a world where information overload is a constant struggle, these algorithms actas digital concierges, curating and delivering the most pertinent and engaging content to our digital doorsteps. They empower us to navigate the vast expanse of the internet with unprecedented efficiency, connecting us with the information, products, and communities that enrich our lives and foster personal growth.As we look to the future, it is clear that the role of algorithms in user-information matching will only grow more pervasive and sophisticated. The advent of advanced technologies like quantum computing and neural networks promises to usher in a new era of algorithmic prowess, enabling even more nuanced and personalized matchmaking capabilities.However, it is incumbent upon us, as users and beneficiaries of these technologies, to remain vigilant and engaged. We must demand transparency, accountability, and ethical oversight to ensure that these algorithms serve our best interests without compromising our fundamental rights and values. By striking the right balance between harnessing the power of algorithmic matchmaking and safeguarding our individual autonomy, we can unlock a future where information flows seamlessly, tailored to our unique needs and aspirations, empowering us to thrive in an ever-evolving digital landscape.In the end, algorithms are not mere lines of code or mathematical equations; they are the digital matchmakers of our modern age, deftly orchestrating the intricate dance between users and information. As we navigate this brave new world, let us embrace the remarkable potential of these algorithms while remaining steadfast in our commitment to using them responsibly and ethically, ensuring that they enhance our lives rather than dictate them.篇3Algorithms: The Key to Efficient User-Information MatchingIn today's world, we are constantly bombarded with an overwhelming amount of information from various sources. Whether it's news articles, social media posts, online videos, or product recommendations, the sheer volume of data can be daunting. However, thanks to the power of algorithms, we can now navigate this vast ocean of information with relative ease, allowing us to find what we need quickly and accurately.As a student, I have experienced firsthand the immense benefits of algorithms in my academic journey. From research papers to online courses, algorithms have played a crucial role incurating and delivering relevant information tailored to my needs and interests.One area where algorithms excel is in personalized learning. Online educational platforms like Coursera, edX, and Khan Academy use sophisticated algorithms to analyze a student's progress, strengths, and weaknesses. Based on this data, they can recommend courses, supplementary materials, and even adjust the difficulty level to ensure an optimal learning experience. This personalized approach not only enhances our understanding but also keeps us engaged and motivated throughout the learning process.Moreover, algorithms have revolutionized the way we search for information on the internet. Search engines like Google and Bing use complex algorithms to crawl, index, and rank web pages based on their relevance to our search queries. These algorithms consider various factors, such as keyword density, page authority, and user behavior, to provide us with the most relevant and trustworthy results. Without these algorithms, we would be lost in the vast expanse of the World Wide Web, unable to find the information we seek efficiently.Another area where algorithms have made a significant impact is in recommendation systems. Online platforms likeAmazon, Netflix, and Spotify use collaborative filtering and content-based algorithms to analyze our preferences, browsing history, and ratings to suggest products, movies, or music that we might enjoy. These recommendations not only save us time but also introduce us to new and exciting options that we might have otherwise missed.Furthermore, algorithms play a crucial role in targeted advertising. While some may view this as intrusive, it's undeniable that algorithms have made advertising more relevant and effective. By analyzing our browsing behavior, location data, and demographic information, algorithms can serve us ads for products or services that align with our interests and needs. This not only benefits businesses by increasing their chances of conversion but also enhances the user experience by reducing irrelevant and annoying advertisements.However, it's important to acknowledge the potential drawbacks and ethical considerations surrounding the use of algorithms. Privacy concerns, algorithmic bias, and the perpetuation of filter bubbles are valid issues that need to be addressed. As users, we must remain vigilant and critical when interacting with algorithmically curated content, ensuring that we are not being unduly influenced or manipulated.Nevertheless, the benefits of algorithms in matching users with relevant information cannot be overstated. They have transformed the way we learn, search, and consume information, making our lives more efficient and enriching our experiences.As a student, I have witnessed firsthand how algorithms have enhanced my academic journey. From personalized learning platforms to targeted research recommendations, algorithms have consistently provided me with the information I need, when I need it. This has not only saved me countless hours of sifting through irrelevant data but has also enabled me to explore new avenues of knowledge that I might have otherwise missed.Moreover, algorithms have facilitated collaboration and knowledge sharing among students and academics. Online forums, discussion boards, and social media platforms use algorithms to surface relevant discussions, research papers, and expert insights, fostering a vibrant and interconnectedacademic community.Looking ahead, the future of algorithms in user-information matching is promising. With the advent of artificial intelligence (AI) and machine learning, algorithms will become even more sophisticated and personalized. They will be able to understandand anticipate our needs more accurately, providing us with tailored information before we even realize we need it.However, as algorithms become more powerful, it is crucial that we address the ethical and societal implications of their use. We must ensure that algorithms are transparent, unbiased, and accountable, and that our privacy and autonomy are protected.In conclusion, algorithms have transformed the way we interact with information, enabling us to navigate the vast expanse of data efficiently and accurately. As students, we have benefited tremendously from personalized learning, targeted research recommendations, and collaborativeknowledge-sharing platforms, all powered by algorithms. While there are valid concerns about privacy, bias, and manipulation, the benefits of algorithms in user-information matching are undeniable. As we move forward, it is our responsibility to embrace the power of algorithms while addressing their potential drawbacks, ensuring that they serve our best interests and enhance our lives in meaningful ways.。

【课件】Unit+4Sharing+Using+language+课件-人教版选择性必修第四册

【课件】Unit+4Sharing+Using+language+课件-人教版选择性必修第四册
【句式分析】now that 是连词词组,表示“既然”,引导表示原因的状 语从句,常位于主句前面。
__N__o_w_ _t_h_a_t__ the kids have left home we’v got a lot of extra space.
孩子们都离开家了,我们住着就更宽绰了。
4. not only…but (also)…
当句中的动词后接多于两个由that引导的宾语从句时,第一个that 可省略,但后面的that不可省略。
3. Now that I understand how important my mother's work is, I've decided to become a volunteer myself to help people in other lands.
Chinese people do to help others overseas? 2. Why was Bingbing upset when her mother
went to Tanzania? 3. What are some of the problems people face
in Tanzania? 4. What are two things that Bingbing's
Scanning
Zhan Bingbing ,a senior high school student, whose mother is a doctor is giving a speech. Read and find out the main idea.
This _s_p_e_e_c_h___mainly shows us _h_o_w_____Zhan Bingbing’s _a_t_ti_t_u_d_e_ towards her mother’s aid to other countries changed and the _____s_ig_n_i_f_ic_a_n_c_e_ of China’s aid to other countries.

英语辅助教具

英语辅助教具

英语辅助教具English Language Learning AidsIntroduction:English language learning can be a challenging task, especially for non-native speakers. To facilitate the learning process and make it more engaging and effective, various English language learning aids have been developed. These aids, ranging from physical materials to digital resources, serve as valuable tools for both teachers and learners. In this article, we will explore some of the most effective and popular English language learning aids, their benefits, and how they can enhance the language learning experience.1. Flashcards:Flashcards have long been recognized as an effective learning aid for vocabulary acquisition. They consist of small cards with a word or phrase on one side and its translation or definition on the other. These cards can be used in various ways, such as matching exercises, memory games, or simply as a reference tool. Flashcards help learners develop word recognition skills, expand their vocabulary, and improve retention.2. Language Learning Apps:With advancements in technology, language learning apps have gained immense popularity. These apps provide interactive and personalized learning experiences. They offer a wide range of features, including interactive lessons, grammar exercises, language challenges, and vocabularyquizzes. Language learning apps are convenient and accessible, allowing learners to practice English anytime and anywhere. Additionally, many of these apps provide pronunciation guides and speech recognition tools to help learners improve their speaking skills.3. Board Games:Board games designed specifically for English language learning add an element of fun and competition to the learning process. These games encourage communication, collaboration, and critical thinking skills. Board games often focus on grammar, vocabulary, and sentence construction. They provide an interactive and engaging environment for learners to practice their language skills in a relaxed setting. Moreover, playing board games in English helps learners develop fluency and confidence in spoken English.4. Listening and Speaking Devices:Listening and speaking devices, such as language labs or digital translators, enable learners to practice their listening and speaking skills in a controlled environment. Language labs provide a range of audio materials, including dialogues, speeches, and interviews, to improve listening comprehension. Learners can then record their responses, allowing them to assess their pronunciation and speaking skills. Digital translators, on the other hand, help learners understand and translate words or phrases in real-time, facilitating comprehension and communication.5. Language Learning Software:Language learning software encompasses a range of computer programs and applications designed to enhance language learning. These programsoffer comprehensive language courses, including grammar, vocabulary, reading, writing, listening, and speaking activities. Language learning software provides learners with interactive exercises, instant feedback, and progress tracking. It allows learners to set personalized goals and work at their own pace, ensuring a customized learning experience.Conclusion:English language learning aids play a crucial role in enhancing the language learning experience. From flashcards to language learning apps and board games, these aids provide a variety of interactive and engaging tools for learners. They improve vocabulary retention, listening comprehension, speaking skills, and overall language fluency. As technology continues to advance, the development of innovative English language learning aids will undoubtedly contribute to more efficient and enjoyable language learning. With the right combination of these aids and effective teaching methodologies, learners can achieve their language learning goals effectively.。

Megger时域追片仪 CFL535G、TDR2010 和 TDR2050 系列商品说明书

Megger时域追片仪 CFL535G、TDR2010 和 TDR2050 系列商品说明书

CFL535G, TDR2010 and TDR2050Advanced Dual Channel TDR■■600 V CAT IV input protection filter built in(Model TDR2050)■■Step and pulse TDR selections ■■Distance dependent gain ■■Test straight from the box ■■Trace tagging ■■2ns pulse width■■Designed for use on all metallic paired cablesDESCRIPTIONThe Megger ® CFL535G, TDR2010 and TDR2050 are state of the art, dual channel, high resolution, compact Time Domain Reflectometers with a color screen for locating faults on paired metallic cables. All TDRs in this series have a minimum resolution of 0.1 m / 0.3 ft and a 20 km / 65 kft maximum range depending on the velocity factor selected and the cable type.Various output impedances are available (25, 50, 75, 100, 125, 140 ohms, model dependent) and an auto impedance matching feature. The velocity factor can be set between 0.2 and 0.99 to meet any cable test requirements.The TDR2050 is the first in its class to have 600 V CATIV input protection filter built in, giving the ability to connect to known live lines. This is particularly useful for detecting illegal taps without having to power down the line.FEATURES AND BENEFITSThe CFL535G, TDR2010 and TDR2050 have a large, high resolution, color, WVGA display with easy set up features. Directional control buttons, together with soft keys, provide intuitive and easy operation for the user.An AUTO selection option ensures that the most effectiveparameters are selected depending on the range required, aiding rapid diagnosis of the TDR trace. The ability to manually override the auto function allows fine tuning to enable identification of hard to determine faults.Dual trace and dual cursor capabilities allow full flexibility, giving the operator full control and instant indication of distance between two points.A trace comparison feature also allows close examination between trace conditions. Extra high resolution together with a white-light backlight, user definable color schemes give the graphical display a vibrance, aiding the user in identifying key events on the trace.600 V CAT IV input protectionTDR2050 is the first TDR in this class to include a built-in 600 V input protection filter. The ability to connect to potentially live circuits means a more flexible instrument suited for a wider range of applications.Trace Storage100 internal trace memories provide for the storage and recall of test results. The traces can be recalled to the display for analysis or compared with an active display to aid in fault location.Alternatively the stored results can be downloaded to a computer, via the USB port, using the TraceXpert software and USB lead provided.Step TDR functionThe dead zone effect of a standard pulse TDR can mask near end faults and make them undetectable. The addition of a step function on the TDR2050 eliminates this problem.Step TDR technology means that the signal is injected at full strength and stays there until a disturbance is detected. This makes step TDR technology perfect for detecting near end faults that standard pulse TDRs can miss.Distance dependent gainThis feature, built into the TDR2050, eliminates the drop off of signal attenuation on longer lines by gradually increasing the gain along the returned signal, enabling a more even representation of the relative attenuation at all points along the trace.Fault identificationMegger’s own built-in AutoFind mode allows for speedy identification of faults. One press of the AutoFind key automatically adjusts the range and gain, and positions the cursor to the first major event on the cable. Press the AutoFind key again and the cursor will jump to the next detected disturbance.FindEnd functionTDR2050 also incorporates a FindEnd function, which allows the user to automatically search the trace to identify the end of the cable under test. This is useful in situations where a fast cable length measurement is required.For those who wish to maintain manual control, manual operation allows full override access to refine the response for easy fault identification.Color schemesThe very different light conditions that could be present when using the TDR2050, combined with the limitations of eye conditions such as color blindness, makes the addition of set color schemes in the instrument extremely important.TDR2010 and TDR2050 have 6 additional set color schemes on top of the Default and Outdoor schemes included on other Megger TDRs. There are also 2 custom slots where the user can specify their own scheme by setting up to 7 screen elements to their own choice of color.Trace TaggingTDR2010 and TDR2050 also incorporate a Trace Tagging feature which allows the user to add a name to saved traces. This could be the circuit ID, building name or any other identifying text the user wishes to save with the trace.A text string of up to 32 alphanumeric characters can be stored against each trace and this can consist of upper case letters including accents.TraceXpert PC softwareThe CFL535G, TDR2010 and TDR2050 come complete withthe Megger TraceXpert software which gives full control over downloading, reporting and uploading of saved trace results. Designed around a database and programmed for ease of use and simplicity, TraceXpert offers the ideal application for all your data processing requirements.Models include:CFL535GA fully featured high resolution TDR with backlit color display and powered by Li-ion rechargeable battery batteries. This model comes complete with 2 pairs of mini-clip Test Leads.TDR2010The same as the CFL535G but with Trace Tagging and additional Color Scheme selection.TDR2050The same as TDR2010 but with the addition of 600 V CAT IV rating, Step, DDG and FindEnd functions.ADDITIONAL FEATURES (MODEL DEPENDENT)■■Backlit graphics color LCD (800x480)■■Adjustable display contrast■■Resolution to 0.1 m■■USB connection to PC allowing upload and download of traces■■For use on Telecom TNV-3 circuit, or 150 V CAT IV power circuits (CFL535G and TDR2010 only)■■For use on power circuits to 600 V CAT IV (TDR2050 only)■■Power blocking filter built-in■■Environmental protection to IP54■■Selectable output impedance (25, 50, 75,100, 125 and 140 Ω)■■2ns pulse for near end fault location■■AUTO option selecting gain and pulse for each range■■AUTO option matches output impedance to cable■■Display distance in meters or feet■■Li-ion rechargeable battery (12 hours typical life) APPLICATIONS■■Personnel involved in the location of cable faults as part of a responsive or routine maintenance program.■■Electrical inspectors during quality checks following work onall new cable installations and modifications to existing cable installations.■■Testing reels of cable for shipping damage, cable shortages, cable usage, and inventory management.■■Testing for faults on hidden cabling in vehicles such as trains and airplanes where access is restricted and voltage may be present.■■Tracking down illegal connections (taps) on the power system.■■Checking for performance on umbilical cables in oceanographic and mining situations.■■Maintaining rail network signal communications and power cabling.■■Ensuring safe and efficient state of commercial heating and air conditioning cable.SPECIFICATIONSExcept where otherwise stated, this specification applies at an ambient temperature of 20°CGENERALRangeUp to 20000 m with a minimum resolution of 0.1 mm ft ns10 30 12525 80 25050 160 500100 320 100250 800 2500500 1600 50001000 3200 100002500 8000 250005000 16000 5000010000 32500 10000020000 65000 200000 Accuracy±1% of range ±1 pixel at 0.67 VF[Note - The measurement accuracy is for theindicated cursor position only and is conditionalon the velocity factor being correct. Resolution1% of rangeInput protection This instrument complies withIEC61010-1 to protect the user in theevent of connection to live systems.TDR2050 is rated at 600 V CAT IVwhie the other models are rated at150 V CAT IV. TDR2050 is specificallydesigned to allow use on energizedsystems up to the rated voltage. Allother models are designed for useon de-energized systems and fusedleads must be used if the potentialvoltage between terminals couldexceed 300 VOutput pulse Up to 20 volts peak to peak intoopen circuit. Pulse widths determinedby range, cable and model used. Gain Set for each range with userselectable steps (in Manual operatingmode)Velocity factor Variable from 0.2 to 0.99 in stepsof 0.01TX null AutomaticTrace Tagging - 32 characters chosenfrom upper case letters includingaccentsColor schemes - Default, Outdoor,CustomStep TDR - Eliminates the Dead Zoneeffect.DDG - Available in ranges 1000 mand above in 0.5 dB stepsCable Impedance - 25, 50, 75, 100,125, 140 ohm + AUTOPower down User programmable auto power offtimer 1, 5, 10 mins or never Battery Li-ion rechargeable batteryBattery charge time 6 hours at 0 °C to 40 °CBattery life12 hours typicalSafety These instruments comply withIEC61010-1 for connections to livesystems up to 150 V CAT IV or 300 VCAT III (2010 only).TDR2050 is rated at 600 V CAT IV.Fused leads must be used if thevoltage between terminals exceeds300 V.Compliant with EN60950-1,EN61010-1, UN38.3 and EN62133 EMC Complies with ElectromagneticCompatibility Specifications (Lightindustrial) BS EN 61326-1, with aminimum performance of ‘B’ for allimmunity tests.MECHANICALIP rating The instrument is designed for useindoors or outdoors and is ratedto IP54.Case ABSDimensions290 mm (11.4 in.) x 190 mm(7.5 in. x 55 mm (2.2 in.)Weight 1.7kg (3.8lbs)Connectors Four 4mm-safety terminals and twoF connectors. Other standard pushon adapters will fit. F connectorsnot available on TDR2050.Test lead 1.5 meters long consisting of2 x 4 mm shrouded connector tominiature crocodile clips(CFL535G and TDR2010) or1.5 meter fused leads (TDR2050) Display800 x 480 pixel color graphics LCD,viewable in external environments.Color SchemesSelectableCFL535G x2TDR2010, TDR2050 x8CustomCFL535G x1TDR2010, TDR2050 x2Backlight Permanent backlight with all colorschemes (adjustable brightness) ENVIRONMENTALOperating temperaturerange and humidity-15 °C to +50 °C (5 °F to 122 °F)<95% at +40 ºC non-condensing Storage temperaturerange and humidity-20 °C to 70 °C (-4 °F to 158 °F)<95% at +40 ºC non-condensingAdvanced Dual Channel TDRCERTIFICATION ISORegistered to ISO 9001:2000 Cert. no. Q 09290Registered to ISO 14001-1996 Cert. no. EMS 61597CFL535G_TDR2010_TDR2050_DS_US_Megger is a registered trademarkUKArchcliffe Road Dover CT17 9EN England T +44 (0) 1304 502101F +44 (0) 1304 207342******************UNITED STATES2621 Van Buren Avenue Norristown, PA 19403 USA T 1 866-254-0962 (USA only) T +1 610-676-8500 F +1 610-676-8625****************************OTHER TECHNICAL SALES OFFICES Dallas TX USA, College Station USA, Sydney AUSTRALIA, Täby SWEDEN, Ontario CANADA, Trappes FRANCE,Oberursel GERMANY, Aargau SWITZERLAND, Kingdom of BAHRAIN, Mumbai INDIA,Johannesburg SOUTH AFRICA, Chonburi THAILANDDescription Cat. No.TDR2050 Power TDR1005-023TDR2010 Dual Channel Comms 1005-449CLF535G Dual channel 1006-138Included accessoriesRetractable sheath fused test leads (1 pair) (TDR2050 only)1005-511Dual lead set with bed of nails clips (CFL535G and TDR2010 only) 6231-655Dual power lead set with fused clips (TDR2050 only) 1002-136Download kit 1003-353Carry case with straps 1003-217AC-DC power charger 1003-352Power cable25970-002Terminal adapter kit with BNC (CFL535G and TDR2010 only) 1003-218User guide CDDescription Cat. No.Optional accessoriesSingle power lead set with fused clips 1002-135Miniature clip test lead set (1 pair) 6231-652Bed of nails test lead set (1 pair) 6231-653Fused 500 mA test lead set (1 pair) 1002-015Replacement battery1002-552Terminal adapter kit (TDR2050 only) 1003-218AC power lead25970-002Dual power lead set with bed of nails clips (TDR2050 only)6231-655Dual fused lead set (CFL535G and TDR2010 only) 1002-136Dual power lead set with fused clips 1003-326Dual miniature clip test lead set 6231-654Short leadset BNC to croc clips 6231-694BNC adapter25965-154Retractable sheath fused test leads (1 pair)1005-511Advanced Dual Channel TDR。

画pcb要注意的点

画pcb要注意的点

画pcb要注意的点英文回答:When it comes to designing a PCB (Printed Circuit Board), there are several key points to keep in mind. As an electrical engineer with experience in PCB design, I have encountered various challenges and learned valuable lessons along the way. Here are some important considerations:1. Component Placement: Proper component placement is crucial for optimal functionality and ease of manufacturing. It is important to place components in a way that minimizes signal interference and ensures efficient routing. For example, sensitive analog components should be placed away from noisy digital components to avoid cross-talk.2. Signal Integrity: Maintaining signal integrity is essential for reliable operation of the PCB. This involves careful consideration of trace lengths, impedance matching, and minimizing signal reflections. For high-speed signals,controlled impedance traces and differential pair routing may be necessary.3. Power and Ground Planes: A well-designed power and ground plane system helps in minimizing noise and providing a stable reference for signals. It is important to have a solid ground plane that connects all ground points and provides a low impedance path for return currents. Similarly, power planes should be designed to provide sufficient power distribution to all components.4. Thermal Management: Heat dissipation is a critical aspect of PCB design, especially for power-intensive applications. Proper placement of heat sinks, thermal vias, and consideration of airflow can help in efficient cooling. Additionally, ensuring that high-power components are adequately spaced and have sufficient thermal relief is important.5. Design for Manufacturability (DFM): Considering DFM guidelines early in the design process can save time and cost during PCB fabrication and assembly. This includesadhering to manufacturing tolerances, choosing appropriate pad sizes, and avoiding complex and costly features like buried vias or blind vias.6. Design for Testability (DFT): Incorporating DFT techniques allows for easier testing and debugging of the PCB. This can include adding test points, boundary scan capabilities, and built-in self-test features. DFT considerations can greatly aid in the troubleshooting process and reduce development time.7. EMI/EMC Compliance: To ensure electromagnetic compatibility and minimize electromagnetic interference, it is important to follow EMI/EMC guidelines. This involves proper grounding, shielding sensitive components, and utilizing filtering techniques to suppress unwanted emissions.中文回答:当涉及到PCB(印刷电路板)设计时,有几个关键点需要注意。

算法可以快速完成用户与信息的精准匹配作文

算法可以快速完成用户与信息的精准匹配作文

算法可以快速完成用户与信息的精准匹配作文Title: The Power of Algorithms in Precise User-Information Matching In today's digital era, the sheer volume of information available can be overwhelming, often leading to challenges in finding relevant and meaningful content. However, the emergence of sophisticated algorithms has revolutionized the way we interact with this vast pool of data.在当今数字化时代,海量的信息常常令人感到无所适从,很难找到相关和有意义的内容。

然而,先进算法的出现彻底改变了我们与这一庞大数据池交互的方式。

Algorithms, through their intricate mechanisms, are capable of quickly analyzing vast amounts of information and pinpointing those pieces that are most relevant to a user's interests or needs.算法通过其复杂的机制,能够迅速分析大量信息,并精确找到与用户兴趣或需求最相关的内容。

This precision matching is achieved by leveraging various techniques, including machine learning and artificial intelligence, which enable algorithms to learn from past interactions and continuously improve their accuracy.这种精确匹配是通过利用各种技术实现的,包括机器学习和人工智能,这些技术使算法能够从过去的交互中学习,并不断提高其准确性。

广东省广雅中学2023-2024学年高一上学期12月阶段测试英语试卷

广东省广雅中学2023-2024学年高一上学期12月阶段测试英语试卷

广东省广雅中学2023-2024学年高一上学期12月阶段测试英语试卷学校:___________姓名:___________班级:___________考号:___________一、单项选择1.In the dark street, there wasn’t a single person ________ she could turn for help.A.for whom B.to who C.to whom D.for who2.I am always grateful for Mr. Vamp, __________ warning I would have been drown in the river the way __________ other children did.A.with whose; /B.whose; in whichC.without whose;/D.without whose; what3.__________ is reported in the news, Harrison has been arrested who is said __________ his neighbour.A.Which; had harmed B.Which; to have harmedC.As; harming D.As; to have harmed4.John as well as the other children who_______no parents_______ good care of in the village.A.have; is being taken B.have; has takenC.has; is taken D.has; have been taken5.She didn’t expect the great trouble she had ________ the problem ________ currently.A.to solve; discussing B.solving; to be discussedC.to solve; discussed D.solving; being discussed6.---There isn’t anything serious, _________,Doctor?---_________.The children will be all right in a day or two.A.is it; Yes B.isn’t ; NoC.isn’t there; Yes D.is there; No7.Time should be made good use of ______ our lessons well.A.learning B.learned C.to learn D.having learned 8.It was in Beihai Park ______ they made a date for the first time ______ the old couple told us their love story.A.that; that B.where; when C.that; when D.where; that 9.The old man has a son and two daughters, ______ treat him well, ______ made him verysad.A.and none of them; that B.none of them; whichC.and none of whom; that D.none of whom; which10.The teacher proposed that the student ________ an opportunity to further his study________ his excellence.A.giving, because of B.be given, because ofC.was given, because D.give, because二、阅读理解As a language learning enthusiast, I’ve come up with the best apps for learning English from the thousands of mobile apps out there.Best for Pronunciation: ELSA SpeakELSA Speak is probably the best mobile app around for helping you improve your English pronunciation. The app’s greatest strength is its intensive AI feedback, but ELSA also provides mini-training sessions to really perfect your pronunciation. The AI analyzes your recordings based on pronunciation, intonation and fluency then points out exactly which parts sound inaccurate.Best for Immersing in English Videos: FluentUFuentU is a language learning app that teaches you English through authentic videos like news reports, movie scenes and interviews, with learner tools for all levels. Each clip has interactive subtitles so if you’re not sure what a word means, you can hover over it and get in explanation. The app also gives video examples for each word so you can learn vocabulary in context.Best for Practical Topics: BabbelBabbel has you learn and practice English with realistic conversations that surround things that you’re personally interested in. Lessons are short and consist of written and audio versions of the grammar featured in the lessons. Then you are able to complete practice exercises to solidify your understanding.Best for Fun Beginner Lessons: LingodeerLingodeer uses games and short exercises to teach beginner and intermediate English learners. Lingodeer takes a gamified approach to language learning with a goal-oriented curriculum consisting of structured lessons and regular reviews. Lingodeer’s lessons arearranged according to themes, such as sports, weather, parts of the body and shopping. 11.What is the feature of ELSA Speak?A.It analyzes learners’ recordings.B.It provides guidance for learners.C.It gives learners helpful feedback.D.It improves learners’ communication skill.12.Which app provides videos as learning resources?A.FluentU.B.ELSA Speak.C.Babbel.D.Lingodeer. 13.What can learners do with the app Lingodeer?A.Design games.B.Study around a theme.C.Structure lessons.D.Take advanced courses.Hotels were full, local specialties were nearly sold out, tourists came in droves from all parts of China… Rongjiang, a small county of Qiandongnan Miao and Dong autonomous prefecture in Guizhou Province, has recently gone viral for its “Village Super League”.Every week, more than 40,000 audiences flooded to the stadium for the “Village Super League”. As of the end of June, 2023, the championship has had more than 20 billion views on the Internet.“This is a soccer carnival deeply rooted in the soil! I’ve covered varieties of sports events, including the FIFA World Cup and the Olympics. But it is really the first time that I have experienced such a down-to-earth and lively scene as this,” said Han Qiaosheng, a Chinese sports TV commentator.During a match in May, Wu Chuguo, a decoration worker from Liubaitang village, Rongjiang County, scored a classic 40-meter goal that ignited the crowd. Wu said he was influenced by elders in his village and fell in love with the sport. In the county, rural soccer matches have taken place regularly since the 1990s. When there was a lack of facilities, soccer players used barren land as a field and wooden stakes (桩) for the posts. The boundaries were marked out with lime powder. When they can’t gather enough players, they play futsal, a soccer-based game played on a smaller hard court.In recent years, the county has focused on gymnastics, soccer, rock climbing and other sports, which has developed outstanding national and provincial-level sporting talent. What sets the Village Super League apart from other sports events are the vibrant displays of ethnic (民族的) cultures and traditions at the championship.“I hope that more and more tourists will come to Rongjiang to watch the matches, enjoy the folk customs and local cuisine, and have fun,” said Xiong Zhuqing, a melon grower who is also a cheerleader. She says she has sold over 10,000 kilograms of watermelons since the start of the championship. As of June 27, a total of 654 new businesses were established, including 91 in the catering sector, 188 in retail, and 195 in agriculture and food processing, the local government said.By combining tourism with sports, Rongjiang has found a creative and meaningful way to promote rural revival and rural economic growth.14.What can we infer from paragraph 4?A.Rural soccer matches are demanding on facilities.B.Wu Chuguo started the sports event at Liubaitang village.C.Rongjiang County has a deep tradition of soccer matches.D.The small court greatly limits soccer players’ performances.15.What is special about the “Village Super League”?A.It covers players from all walks of life.B.It combines ethnic elements with sports.C.It aims to select athletes for national-level games.D.It has a cheering team consisting of football fans.16.What do the statistics in the last but one paragraph tell us?A.The matches can help promote economic growth.B.Rongjiang’s tourism has fueled the sports industry.C.Selling agricultural products is key to rural vitalization.D.Local companies have offered significant financial support to the matches. 17.Where can we find this passage?A.Science magazine.B.Tourism brochure.C.Newspaper.D.Textbook.It is reported that endangered polar bears are breeding (繁殖) with grizzly bears (灰熊), creating “pizzly” bears, which is being driven by climate change.As the world warms and Arctic sea ice thins, starving polar bears are being forced ever further south, where they meet grizzlies, whose ranges are expanding northwards. And with that growing contact between the two come increasing hybrids (杂交种).With characteristics that could give the hybrids an advantage in warming northern habitats, some scientists guess that they could be here to stay. “Usually, hybrids aren’t better suited to their environments than their parents, but these hybrids are able to search for a broader range of food sources,” Larisa DeSantis, an associate professor of biological sciences at Vanderbilt University, told Live Science.The rise of “pizzly” bears appears with polar bears’ decline: their numbers are estimated to decrease by more than 30% in the next 30 years. This sudden fall is linked partly to “pizzly” bears taking up polar bears’ ranges, where they outcompete them, but also to polar bears’ highly specialized diets.“Polar bears mainly consumed soft foods even during the Medieval Warm Period, a previous period of rapid warming,” DeSantis said, referring to fat meals such as seals. “Although all of these starving polar bears are trying to find alternative food sources, like seabird eggs, it could be a tipping point for their survival.” Actually, the calories they gain from these sources do not balance out those they burn from searching for them. This could result in a habitat ready for the hybrids to move in and take over, leading to a loss in biodiversity if polar bears are replaced.“We’re having massive impacts with climate change on species,” DeSantis said. “The polar bear is telling us how bad things are. In some sense, “pizzly” bears could be a sad but necessary compromise given current warming trends.”18.Why are polar bears moving further south?A.To create hybrids.B.To expand ranges.C.To contact grizzlies.D.To relieve hunger.19.What enables “pizzly” bears to adapt to natural surroundings better than their parents?A.Broader habitats.B.Climate preference.C.More food options.D.Improved breeding ability.20.What does the underlined phrase “a tipping point” in paragraph 5 refer to?A.A rare chance.B.A critical stage.C.A positive factor.D.A constant change.21.What’s the main idea of the text?A.Polar bears are changing diets for climate change.B.Polar bears have already adjusted to climate change.C.“Pizzly” bears have replaced polar bears for global warming.D.“Pizzly” bears are on the rise because of global warming.Is my article mid or valid? If you can answer this question, you already are used to what we term “algospeak.” As more and more online users join social media platforms such as TikTok (抖音), algospeak continues to grow. But what is it, what do these words mean?Algospeak is a coded language or slang used online. For some communities it is the only way to talk safely about sensitive subjects. Due to the rise of algorithmic censorship (算法筛查) in media, algospeak developed as a way to prevent robot from deleting their videos and messages. Users had to get creative to avoid deletion. This means that as long as there is censorship, there will be a new language to avoid it.Further, new slang created on social media platforms fits itself into everyday life. Even if you are not writing a message on TikTok, you may have caught yourself using phrases from the app in your daily life. This connection between people all over the globe allows for shared vocabulary. It also has the potential to completely change the way we as English speakers speak. Here is some new slang popularized by TikTok.Bussin’ (adj.) — something is really good, usually referring to foodMid (adj.) — ordinary, not good or badSheesh (ex.) — response either meaning disbelief or surprise, can be positive or negative Valid (adj.) — something very good or meets a very high standard; a respectable opinion No one would have expected artificial intelligence (AI) would be the catalyst (催化剂) for change but it is. The combination of not only censorship but also high connectivity birthed a new language. Some older generations can’t even understand what the youngest generation says because of the lack of access to the new language. The gap between English before social media and English as it is now is huge, and it continues to grow.So, what should we expect for the future? Will censorship loosen or will the English language continue to develop from digital media? Time can only tell.22.What contributed to the appearance of algospeak?A.The need for netizens to escape censorship.B.The desire for a shared vocabulary around the world.C.The authority’s demand for creating a new language.D.The social media’s intention to catch public attention.23.What can we learn from the last two paragraphs?A.AI needs catalyst to develop.B.Social media birthed a new language.C.Algospeak may cause communication obstacles.D.Strict censorship is a barrier to interpersonal relationships.24.What is the author’s attitude towards the future of algospeak?A.Optimistic.B.Indifferent.C.Doubtful.D.Unclear. 25.What can we infer about algospeak?A.It offers a new outlook on life.B.It has reshaped the digital media.C.Its development is associated with AI.D.It has won popularity among all ages.A cobra (眼镜蛇) was set free on September 10 in a park in Xiangtan City, Southprevent it from hurting anyone.In the name of mercy, some people free captive (关在笼子里的) animals, including foreign species, mostly bought from pet shops or markets. 27 Last April, someone freed hundreds of foxes and raccoon dogs in a Beijing suburb, causing economic losses to animal farmers and endangering the safety of local residents.28 Besides, today people are increasingly aware of the importance of environmental protection and biodiversity. But it is necessary to ensure that acts of freeing captive animals do not violate laws or harm the interests of the public. 29 In order to regulate the release of captive animals, the government revised the law on wildlife conservation in 2016. According to the updated regulations, no individual or organization should harm the public interest by freeing captive animals. 30 A.And any creatures set free should be local species that have no threat to local biodiversity.B.However, their warm-hearted kindness often causes serious consequences.C.Freeing a cobra in a park reflects the troublemaker’s ignorance of other people’s lives.D.Such news has frequently appeared in recent years.E.Local police immediately arrested the troublemaker.F.Influenced by Buddhism, freeing captive animals is an act that deserves respect inChina.G.It is important to protect animals including those set free by people.三、完形填空On the April morning I found out about Lucy’s mother, it rained. I didn’t know what kind of cancer Mrs. Hastings had until later, 31 I knew her condition was very serious.I love Mr. and Mrs. Hastings almost as much as I love my own parents, and Lucy is my best friend. But I didn’t want to go to school that day. And I 32 didn’t want to see Lucy.What could I possibly say to her? What do people say to their friends at such a time? I tried every trick I knew to get out of going to school.But Mom 33 . “You have a history test this morning, Kristin,” she said, looking at me as if she’d crawled into my mind and knew I was just making 34 . Then she smiled. “Be sure to stay close to Lucy, especially today, because that poor girl is going to need your strength.”Strength? What was Mother talking about? I didn’t even know what to say to my best friend. I hid out in the choir room between classes 35 avoiding Lucy, but she was never out of my thoughts. I kept trying to come up with something 36 to say to her because I really wanted to get it right.Lucy and I had last-period English in Mrs. Green’s room. I’d avoided meeting her all day, I was going to have to face her last period, and I still didn’t have a(n) 37 . However, Mrs. Green said, “Kristin, Lucy Hastings is your best friend, and she is coming here in a few minutes to get her lesson assignments.”My heart tightened into a hard knot and I 38 inwardly. I still didn’t know what to say to Lucy, and time was running out.I rushed out of the classroom, racing down the hall and out the front door of school. It had stopped raining, and the air smelt clean and fresh. In the distance I 39 someone coming toward me, stumbling across the campus. I knew it was Lucy 40 I couldn’t see her face. As she was approaching, I noticed how Lucy’s shoulders shook with every step she took. She must be crying. The rain came down 41 . Raindrops mingled with my tears. Lucy’s heart was breaking, and I wasn’t doing a thing to help her!As I drew nearer to her, my throat tightened, making it impossible to 42 . I prayed for 43 and forced myself to move forward, 44 outstretched. “Oh. Kristin!” Lucy cried. “I was hoping it was you.” We hugged then. It was then that I learned something that I might never have grasped in any other way. I’d been always focusing on myself: What should I do? How should I act? What would I say to Lucy? But when we finally came face to face, I forgot myself and centered on Lucy and her needs. Only when I did that was I able to share Lucy’s grief and let her know that she was 45 and that I really cared.31.A.but B.and C.so D.if 32.A.abruptly B.apparently C.surely D.scarcely 33.A.agreed B.insisted C.hesitated D.swore 34.A.efforts B.sense C.excuses D.mistakes 35.A.in the wake of B.in hopes of C.in pursuit of D.in light of 36.A.personal B.discouraging C.unusual D.appropriate 37.A.plan B.explanation C.goal D.clue 38.A.rocked B.calmed C.sprang D.trembled 39.A.realized B.spotted C.greeted D.expected 40.A.in case B.as long as C.even though D.as though 41.A.again B.suddenly C.expectedly D.surprisingly 42.A.tell B.react C.scream D.speak 43.A.determination B.strength C.courage D.fortune 44.A.palms B.legs C.shoulders D.arms 45.A.special B.outstanding C.good D.sad四、语法填空The airport covers an area of about 150 square kilometers, 50 the terminal building (候机楼) alone covering 780,000 square meters, equivalent to 100 standard football fields. It is worth mentioning that the clever design takes passengers 51 (little) than eight minutes to walk to any gate from the center of the terminal.The airport is also 52 “intelligent airport”, with thousands of intelligent devices and tens of thousands of sensors. The airport 53 (inform) center is run with cutting-edge technologies including cloud computing and 5G, 54 (contribute) to passengers’ comfort and convenience.With the help of face check-in, self-service check-in, mobile phone query luggage location… in Beijing Daxing International Airport, you can feel the new travel experience 55 (bring) by high technology. More Chinese miracles are happening in this land.56.This (refer) book, though published years ago, is still up to date.(所给词的适当形式填空)57.There are (variety) activities for the teenagers to choose from. (所给词的适当形式填空)58.It is hard to make a (compare) with her previous book because they are totally different. (所给词的适当形式填空)59.The paintings were in an excellent state of (preserve). (所给词的适当形式填空)60.We believe in (equal) between men and women. (所给词的适当形式填空)五、单词拼写拼写)62.She is giving a detailed (描述) of what she has seen. (根据汉语提示单词拼写)63.She asked for (原谅) for what she had done wrong. (根据汉语提示单词拼写) 64.(尽管) applying for hundreds of jobs, he is still out of work. (根据汉语提示单词拼写)65.At that time, they had to (斗争) against natural disasters. (根据汉语提示单词拼写)66.The test questions are kept secret so as to (to stop something from happening) cheating. (根据英文提示单词拼写)67.The painting reflected the artist’s intelligence and (the ability to create new ideas). (根据英文提示单词拼写)68.Mr. Wang doesn’t agree to my (a plan or suggestion) that we should have a picnic this weekend. (根据英文提示单词拼写)69.He wrote a book to (to record something in writing or on film) his sailing experiences. (根据英文提示单词拼写)70.The task was so (needing a lot of time, ability, and energy) that Alice needs to work hard at it. (根据英文提示单词拼写)六、完成句子七、书信写作81.假如你是新华高中的学生李华,近年全球掀起了学汉语的热潮。

大学生就业英文

大学生就业英文

大学生就业英文ﻭﻭﻭﻭ就业的含义是指在法定年龄内的有劳动能力和劳动愿望的人们所从事的为获取报酬或经营收入进行的活动。

那么今天给大家带来了大学生就业英文,希望大家喜欢。

大学生就业英文:In todays increasingly petitive world, wecolleges tudents neednot onlya goodlevelofknowledge, but alsoaproper career planng。

ﻭEveryone tsto ownlifecan be avery fascinat ing,so should he their own career planng,especially forcollege students,the employment planngfor career development andits imrtant sigficance.The sigficanceof career planng is tofind a car eer that suits its development needs,torealize thematching between individual and profession, and to maximizethe value of the individual.We should ac knowledge and correct the deficiencies and gapsin our professionalinterest traingand career education。

In order tomake up this gap,wecan do a good job in guiding the employmentof collegestudents in China, and we canstart from boththe individual andthe society.ﻭﻭTo he asuccessfulcareer plan,youshould he the right premise and clear goal, and thecareer ideal will serve as theleader and guide in thecareer of the person。

一种快速的单模式匹配算法

一种快速的单模式匹配算法

一种快速的单模式匹配算法杨子江;聂瑞华【摘要】After analyzing BM algorithm and some important improved algorithms , a new improved algorithm called Y_BMHS is put forward .With a two-dimensional array , the algorithm considers the uniqueness of text string's last two interval characters and pattern string's first character .The proposed algorithm makes the maximum displacement enhance to m+3, and the occurrence probability and match speed are also improved .The experimental results show that the Y_BMHS algorithm performs better than BM , BMH, BMHS and other improved algorithms as well .%在分析了BM算法以及一些重要的改进算法的基础上,提出一种新的改进算法---Y_BMHS 算法。

利用辅助的二维数组,考虑了文本串后间隔的两位字符和模式串首字符的唯一性,使得最大位移提升到m+3,出现概率也显著提高,加快了匹配速度。

证明Y_BMHS算法比BM、BMH、BMHS等算法有更好的性能。

【期刊名称】《华南师范大学学报(自然科学版)》【年(卷),期】2013(000)005【总页数】5页(P31-35)【关键词】BMHS算法;二维数组;出现概率;BMH算法;BM算法【作者】杨子江;聂瑞华【作者单位】华南师范大学计算机学院,广东广州510631;华南师范大学计算机学院,广东广州510631; 华南师范大学网络中心,广东广州510631【正文语种】中文【中图分类】TP301.6模式匹配是指在文本串 T=T[0]T[1]…T[n-2]T[n-1]中查找 P=P[0]P [1]…P[m-2]P[m-1].该技术广泛应用于信息检索、数据挖掘、模式识别和入侵检测等领域,而匹配算法的好坏直接影响该系统效率.模式匹配分为多模式串匹配和单模式串匹配,多模式串匹配算法有AC算法[1]等其他一些改进算法,单模式串匹配的主要算法有BF算法[2]、KMP算法[3]和 BM 算法[4]等.BM 及其改进算法(如 BMH算法[5]、BMHS算法)由于效率较高而被广泛应用.本文首先介绍BM算法和改进算法BMH、BMHS等,分析各种算法的优缺点,在此基础上提出一个新的单模式匹配算法——Y_BMHS.1 相关算法介绍假设文本串 T=T[0]T[1]T[2]…T[n-2]T[n-1],长度是 n;模式串 P=P [0]P[1]P[2]…P[m-2]P[m-1],长度是m;匹配进行到文本串的j处,现在就BM算法以及改进算法作简单的介绍.1.1 BM、BMH、BMHS 算法1977 年,BOYER 和 MOORE[4]提出了 BM 算法.BM算法是先将模式串P与文本串T左对齐,从P的最右端字符往左开始匹配,一直到P中的字符全部匹配成功或者是有不匹配的字符出现时循环结束.算法采用根据2个预先定义的跳跃数组Badchar和Goodsuffix计算出的位移量进行移动.Badchar和Goodsuffix根据已匹配的字符串和未匹配字符的位置进行计算.当文本串字符与模式串字符失配时,根据数组Badchar和Goodsuffix取其中较大者为shift的值,将模式P往右移shift个字符,继续进行下一轮匹配,匹配成功则直接输出.BM算法考虑全面,包括了右移时的所有情况,但它使用了2个数组,预处理花费太多时间,程序实现复杂,并且Badchar被选为shift的值出现的概率远比Goodsuffix的大,而在匹配过程中两者都用,进行了大量不必要的比较,降低了匹配速度.HORSPOOL[5]于 1980 年提出了 BMH 算法,该算法将匹配字符串与计算右移量独立,即在计算右移量时不关心匹配位置和匹配情况.当发生失配时,通过与模式串末端对应的文本串位置的字符计算右移量.BMH算法较BM算法有更好的性能,它只使用了Badchar数组,简化了预处理过程,并且省去比较shift值的过程,实践也证明BMH性能更优.它仅仅通过一个字符计算右移量,增加了很多不必要的比较和移动.SUNDAY[6]于1990年在BMH算法的基础上又提出了改进的BMHS算法.其主要改进思想是:在计算Badchar函数时,利用模式串末端对应的文本串位置的下一字符决定右移量.当比较进行到文本串 j位置,失配发生在 T[i+j]=b 与 P[i]=a 处,只使用T[j+m]=c决定右移量.当发生失配时,若c未出现在P中,则直接右移m+1位,否则与P中从右往左第一次出现的相同字符对齐,继续进行下一轮匹配.该算法中,当下一个字符T[j+m]未出现在模式中时,它的右移量比BMH算法的右移量大,BMHS算法右移m+1位,BMH算法只能右移Badchar[j+m-1]位置,最多移动m位,故BMHS算法通常比BMH算法快.而当T[j+m-1]不在模式中出现而T[j+m]出现时,BMHS算法就比BMH算法慢.1.2 N_BMHS、IBMHS、Im_Sunday 算法N_BMHS算法[7]是在 BMHS算法的基础上,引入一个数组S标记模式串中字符出现的次数,并在匹配过程上采用两端向中间交替匹配的顺序,一旦失配,利用已匹配位置和辅助数组S的信息进行移动,有效减少了移动和比较次数.IBMHS算法[8]综合了BMH和BMHS算法的特点,并利用频度函数使得最大位移m+1出现频率提高,从而降低匹配时间.算法的主要过程是:在第j轮匹配中,分别计算出采用BMH和BMHS算法启发规则得到的窗口移动值qsBc[T[j+m-1]]-1和qsBc[T[j+m]]并进行比较.若后者大于前者,直接移动qsBc[T [j+m]],否则根据字符出现的频次进行(m+1)或 qsBc[T[j+m-1]]-1的移位.Im_Sunday算法[9]使用与模式串最右端对应的文本串字符的下一个字符 S [next]和 S[nnext].S[nnext]是 S[next]后面 m 长度位置的字符,即nnext=next+plen.当 S[next]字符在模式串中出现时,匹配方法与BMHS算法相同.当S[next]字符未在模式串中出现时,判断S[nnext]字符是否出现在模式串中.若出现,将模式串中最右端第一个出现的字符与S[nnext]对齐,否则将整个模式串移动到 S[nnext]的右侧.1.3 算法分析在以上算法中,BM算法是最全面和最复杂的算法,它充分考虑了所有的可能性,但预处理花费太多时间,并且在选择shift值和匹配上进行了太多次不必要的比较.BMH较BM算法有改进,它只采用坏字符的移动规则,并且将字符匹配和计算位移量独立,加快了匹配速度.BMHS是在BMH的基础上进行的改进,其最大位移是m+1,BMH则是m,通常情况下BMHS要比BMH算法的速度更快.IBMHS算法综合了前两者的优点,并利用字符出现次数提高了最大位移m+1的频率.N_BMHS利用已匹配位置和频度数组,能有效减少移动和比较次数.Im_Sunday算法在匹配过程中利用了 S[next]和S[nnext]字符,在一定程度上减少了比较.然而,上述匹配算法仅仅利用模式串末端字符对应的文本串的一个字符或下一字符的信息进行跳跃,从而进行了很多次不必要的比较和跳跃,且其跳跃距离和最大跳跃距离出现概率均偏小,造成匹配速度变慢.模式匹配存在2个基本定理:任何文本串匹配算法在最坏情况下必须检查文本串中至少n-m+1个字符;任何模式匹配算法至少检查 n/m个字符[10].因此,没有一个算法的计算复杂度比BM算法及其改进算法还要优越,但是我们可以通过增加偏移量,减少匹配次数,获得更好的性能.2 改进算法——Y_BMHS算法根据概率论的理论,2个字符出现在文本串中的概率远小于一个字符出现的概率,所以通过创建一个二维数组,既可以增大最大位移,又可以提高最大位移出现的概率,而有一些模式串的特点是:有大量重复的前缀和后缀如in、ex、ly和组合字符串如ea、se、at等,Y_BMHS算法正是基于这样的想法,结合模式串本身的特点,在BMHS算法的基础上,采用与模式串末端对应的文本串位置(i-1)的下2个字符T[i]和 T[i+2](非连续字符)和模式串首字母的唯一性来计算位移量,非连续字符在一定程度下可以加快匹配速度.该算法将T[i]和T[i+2]作为一个子串,在模式串中出现时,则右移模式串使得子串与文本串从右往左出现的相同子串对齐,否则根据不同情况进行右移处理,最大位移为m+3,其中m是模式串的长度.下面以算法的预处理阶段和匹配阶段做详细阐述.2.1 预处理阶段因为使用2个字符的子串决定右移量,所以我们采用辅助的二维数组来表示位移量.预处理阶段主要是对该位移量数组进行初始化.假设m是模式串P的长度,i 是匹配过程中模式串末端对应的文本串的下一位置,则子串为 T[i]T[i+2].对数组进行如下初始化:第一步,将数组初始值置为m+3;第二步,考虑如下几种特殊情况:(1)当T[i]=P[m-1]时,文本串可能匹配.此时,模式串右移1位,置值为1,如图1A.(2)当T[i]=P[m-2]时,文本串可能匹配.此时,模式串右移2位,置值为2,如图1B.(3)当 T[i+2]=P[1]时,文本串可能匹配.此时,模式串右移m+1位,置值为m+1,如图1C.(4)当 T[i+2]=P[0]时,文本串可能匹配.此时,模式串右移m+2位,置值为m+2,如图1D.第三步,当子串在模式串P中出现时,将其与P中从右到左第一次出现的子串对齐.图1 4种可能的匹配情况Figure 1 Four possiblematch situations2.2 匹配阶段在匹配阶段中,研究了Im_Sunday算法并对其进行了改进.根据概率论的理论,发生失配时,循环判断此时的位移量.若位移量为m+3,则模式串向右移动m+3,并继续循环,否则退出循环进行下一轮匹配.考虑一种特殊情况,如图2示.图2 右移后匹配Figure 2 Match after rightmove此时,右移量还是m+3,但明显已经匹配了,所以在循环中须加入判断.综上所述,实际的匹配流程如图3示.根据上述算法的描述,以T=“Manyarygycnobgtifintromtnology”,P=“nology”为例进行搜索.开始匹配时,把模式串与文本串自左边对齐.具体匹配过程如表1所示.(1)第1 次:T[6]=‘y’=P[m-1],模式串右移1位.(2)第2次:T[7]=‘g’=P[m-2],模式串右移2位.(3)第3次:T[10]=‘n’=P[0],模式串右移m+1位.(4)第4次:T[18]=‘n’=P[0],模式串右移m+2位.(5)第5 次:T[24]T[26]=“nl”,P 中存在该子串,根据跳跃表移动6位,找到字符串,匹配结束.图3 Y_BMHS算法的匹配流程Figure 3 Match process of Y_BMHS表1 Y_BMHS算法匹配过程Table 1 Thematch process of Y_BMHS algorithmM a n y a r y g y c n o b g t i f i n t r o m t n o l o g y 0 n o l o g y 1 n o l o g y 2 n o l o g y 3 n o l o g y 4 n o l o g y 5 n o l o g y2.3 算法分析从Y_BMHS算法的匹配过程可以看出,它是一种典型的以空间换取时间的算法.BMH、BMHS算法在比较时每次只取一个字符进行比较,当发生失配时,以P中某位置对应的文本串的字符T[i]的位移量作为P的移动距离.这种情况下,只有当T[i]不在P中出现时,模式串才能获得最大移动距离.从概率上来说,2个连续字符出现在模式串中的概率远远低于一个字符出现的概率,模式串的特性又使得间隔的两字符在模式串中出现的概率一般低于2个连续字符出现的概率,Y_BMHS算法以间隔2个字符计算偏移量作为P的移动距离,模式串获得最大移动距离m+3的概率也大得多,并且在匹配阶段通过位移量的判断,最大限度地提高了移动距离,这样显然可以获得更高的匹配速度.3 算法性能测试本实验使用的计算机硬件平台为Intel(R)CoreTM i5-2430 M处理器,4 G内存,软件平台为Windows7 64位操作系统,MicroSoft Visual Studio 2010集成开发环境.现采用随机函数产生一段随机长度为500~1 000的文本串和随机长度为5~10的模式串,分别用 BM、BMH、BMHS、IBMHS、Im_Sunday、Y_BMHS 算法进行匹配测试,测试程序与算法均用C语言编写,用主程序调用这6种匹配算法,匹配算法中均插入CPU内部时间戳进行高精度计时,同时统计每种算法一次匹配中平均位移量等数据.实验结果见表2.表2 实验结果比较Table 2 Experimental results算法BM BMH BMHS IBMHS Im_Sunday Y_BMHS一次匹配中最大位移出现的概率0.706 0.745 0.741 0.907 0.709 0.757一次匹配中平均位移量/次 6.817 6.679 7.497 8.671 6.975 9.583 1 000万次匹配消耗时间/s 22.152 13.604 11.856 13.151 11.341 6.630通过上述实验测试可知,Y_BMHS算法在单模式匹配算法中,平均位移量更大,最大位移出现的概率更高,能够快速提高匹配速度,对模式串匹配有更明显的加速效果.4 结束语Y_BMHS算法采用辅助的二维数组记录位移量,通过对模式串末端字符对应的文本串位置的下2个间隔字符的比较,并且在匹配阶段尽可能地使模式串右移,使得模式串以最大位移量m+3进行右移的几率变得更大.通过对算法的分析和实验证明,该算法能够有效地增加模式串右移量,大幅度提高匹配速度,降低匹配时间.参考文献:[1]AHO A V,CORASICK M J.Efficient string matching:An aid to bibliographic search[J].Commun ACM,1975,18(6):333-340.[2]CHARRAS C,LECROQ T.Exact string matching algo-rithms[EB/OL].(1997-01-14)[2012-04-03].http://www.r-igm.univ-mlv.fr/lecroq/string.[3]KNUTH D E,MORRIS JH,PRATT V R.Fast pattern in strings [J].SIAM JComput,1977,6(2):323-350.[4]BOYER R S,MOORE JS.A fast string searching algorithm [J].Commun ACM,1977,20(10):762-772.[5]HORSPOOL N R.Practical fast searching in strings[J].Software Practice and Experience,1980,10(6):501-506.[6]SUNDAY D M.A very fast substring search algorithm[J].Comm ACM,1990,33(8):132-142.[7]单懿慧,蒋玉明,田诗源.面向入侵检测的改进BMHS模式匹配算法[J].计算机工程,2009,35(24):170-173.[8]岳成刚.基于 Snort平台的网络入侵检测系统研究[D].合肥:合肥工业大学,2009.[9]武旭东.Snort入侵检测系统研究与应用[D].吉林:吉林大学,2011.[10]李雪莹,刘宝旭.字符串匹配技术研究[J].计算机工程,2004,30(22):24-26.。

字符串匹配算法比较

字符串匹配算法比较

主要过程:通过对字串进行预处理,当发现不能匹配时,可以不进行回溯。
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C++标准库中总共定义了多少个 (1) IO对象? gml文件格式解析程序详解之源文件 (1)
字符串匹配算法比较
分类: C语言之精深学习 airfer 2013­05­20 18:46 1156人阅读 评论(0) 收藏 举报
字符串匹配(string match)是在实际工程中经常会碰到的问题,通常其输入是原字符串(String)和子串(又称模式, Pattern)组成,输出为子串在原字符串中的首次出现的位置。通常精确的字符串搜索算法包括暴力搜索(Brute force),KMP, BM(Boyer Moore), sunday, robin­karp 以及 bitap。下面分析这几种方法并给出其实现。假设原字符 串长度M,字串长度为N。
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字符串匹配算法比较 ­ airfer 的专栏 ­ 博客频道 ­
2, KMP.
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This paper describes a simple, efficient algorithm to locate all occurrences of any of a finite number of keywords in a string of text. The algorithm consists of constructing a finite state pattern matching machine from the keywords and then using the pattern matching machine to process the text string in a single pass. Construction of the pattern matching machine takes time proportional to the sum of the lengths of the keywords. The number of state transitions made by theng the text string is independent of the number of keywords. The algorithm has been used to improve the speed of a library bibliographic search program by a factor of 5 to 10. Keywords and Phrases: keywords and phrases, string pattern matching, bibliographic search, information retrieval, text-editing, finite state machines, computational complexity. CR Categories: 3.74, 3.71, 5.22, 5.25
Copyright © 1975, Association for Computing Machinery, Inc. General permission to republish, but not for profit, all or part of this material is granted, provided that ACM's copyright notice is given and that reference is made to this publication, to its date of issue, and to the fact that reprinting privileges were granted by permission of the Association for Computing Machinery. Authors' present addresses: A. V. Aho, Bell Laboratories, Murray Hill, N.J. 07974. M. J. Corasick, The MITRE Corporation, Bedford, Mass. 01730.
output.
o u t p u t ( s ' ) # empty, then the machine emits the set o u t p u t ( s ' ) along with the position of the current input
2. A Pattern Matching Machine
This section describes a finite state string pattern matching machine that locates keywords in a text string. The next section describes the algorithms to construct such a machine from a given finite set of keywords. In this paper a string is simply a finite sequence of symbols. Let K = {Yl,Y2 . . . . . Yk} be a finite set of strings which we shall call keywords and let x be an arbitrary string which we shall call the text string. Our problem is to locate and identify all substrings of x which are keywords in K. Substrings may overlap with one another. A pattern matching machine for K is a program which takes as input the text string x and produces as output the locations in x at which keywords of K appear as substrings. The pattern matching machine consists of a set of states. Each state is represented by a number. The machine processes the text string x by successively reading the symbols in x, making state transitions and occaCommunications of the ACM June 1975 Volume 18 Number 6
Programming Techniques
G l e n n Manacher Editor
Efficient String Matching: An Aid to Bibliographic Search
Alfred V. Aho and Margaret J. Corasick Bell Laboratories
1. Introduction
In many information retrieval and text-editing applications it is necessary to be able to locate quickly some or all occurrences of user-specified patterns of words and phrases in text. This paper describes a simple, efficient algorithm to locate all occurrences of any of a finite number of keywords and phrases in an arbitrary text string. The approach should be familiar to those acquainted with finite automata. The algorithm consists of two parts. In the first part we construct from the set of keywords a finite state pattern matching machine; in the second part we apply the text string as input to the pattern matching machine. The machine signals whenever it has found a match for a keyword. Using finite state machines in pattern matching applications is not new [4, 8, 17], but their use seems to be frequently shunned by programmers. Part of the reason for this reluctance on the part of programmers may be due to the complexity of programming the conventional algorithms for constructing finite automata from regular expressions [3, 10, 15], particularly if state minimization techniques are needed [2, 14]. This paper shows that an efficient finite state pattern matching machine can be constructed quickly and simply from a restricted class of regular expressions, namely those consisting of finite sets of keywords. Our approach combines the ideas in the Knuth-Morris-Pratt algorithm [13] with those of finite state machines. Perhaps the most interesting aspect of this paper is the amount of improvement the finite state algorithm gives over more conventional approaches. We used the finite state pattern matching algorithm in a library bibliographic search program. The purpose of the program is to allow a bibliographer to find in a citation index all titles satisfying some Boolean function of keywords and phrases. The search program was first implemented with a straightforward string matching algorithm. Replacing this algorithm with the finite state approach resulted in a program whose running time was a fifth to a tenth of the original program on typical inputs.
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