线性代数的Matlab口令

The Very Basics
Variables, Vectors, and Matrices
Loops and Functions
Plotting and Graphics
EE 20: Linear Methods for Engineering Analysis and Design Using MATLAB
disp(’Hello world!’) 2 + 5*cos(pi/6)ˆ2 - 3*sin(pi/8) disp(’Goodbye world...’)
At the command prompt:
>> test Hello world! ans = 4.6019 Goodbye world...
The Very Basics
>> x = [1:2:10] x = 1 3 5 7 9
The Very Basics
Variables, Vectors, and Matrices
Loops and Functions
Plotting and Graphics
Vectors with Sequential Entries
Can be used in concatenation:
You can prepare files consisting of MATLAB commands to be executed in order. They need to have a “.m” extension. For example, let the contents of file test.m be
>> x = linspace(0,10,6) x = 0 2 4 6 8 10
>> x = linspace(10,0,6) x = 10 8 6 4 2 0
The Very Basics
Variables, Vectors, and Matrices
Loops and Functions
Plotting and Graphics
The sum and prod Commands
To add or multiply all the entries of a vector:
>> sum([1 3 4]) ans = 8 >> prod([1 3 4]) ans = 12
It does not matter whether it is a row or column vector.
>> x = [1:2:7 12:4:20] x = 1 3 5 7 12 16 20
[stepsize] can be negative:
>> x = [12:-4:0] x = 12 8 4 0
The default [stepsize] is 1:
>> x = [1:5] x = 1 2 3 4 5
Lecture 1 Introduction to MATLAB
The Very Basics
Variables, Vectors, and Matrices
Loops and Functions
Plotting and Graphics
Command Prompt
Enter commands at the prompt
>> x = pi x = 3.1416
to assign variable x the value π. Use ; to suppress the response:
>> x = pi;
Example for using variables afterwards:
>> y = cos(x); >> z = yˆ2 z = 1
>>
Example:
>> 2 + 3 ans = 5
Another example:
>> pi ans = 3.1416
The Very Basics
Variables, Vectors, and Matrices
Loops and Functions
Plotting and Graphics
M Files
Using [first]:[stepsize]:[last] syntax gives
>> 1:2:9 ans = 1 3 5 7 9
To assign to a vector:
>> x = [1:2:9] x = 1 3 5 7 9
The [last] value来自does not have to match the actual last entry:
or
>> x = [1 8 9]’;
Addition/subtraction of vectors, and multiplication/division by a scalar are as usual:
>> x = [1 8 9]; >> y = [3 4 6]; >> z = 2*x + y z = 5 20 24
>> help format FORMAT Set output format. FORMAT with no inputs sets the output format to the default appropriate for the class of the variable. For float variables, the default is FORMAT SHORT. FORMAT does not affect how MATLAB computations are done. Computations on float variables, namely single or double, are done in appropriate floating point precision, no matter how those variables are displayed. Computations on integer variables are done natively in integer. Integer variables are always displayed to the appropriate number of digits for the class, for example, 3 digits to display the INT8 range -128:127. FORMAT SHORT and LONG do not affect the display of integer variables. FORMAT may be used to switch between different output display formats of all float variables as follows: FORMAT SHORT Scaled fixed point format with 5 digits. FORMAT LONG Scaled fixed point format with 15 digits for double and 7 digits for single. FORMAT SHORT E Floating point format with 5 digits. FORMAT LONG E Floating point format with 15 digits for double and 7 digits for single. . . .
The Very Basics
Variables, Vectors, and Matrices
Loops and Functions
Plotting and Graphics
Vectors with Sequential Entries
Another method is to use linspace
The Very Basics
Variables, Vectors, and Matrices
Loops and Functions
Plotting and Graphics
Variables
No need to reserve space in the memory beforehand. For example, you just write
The Very Basics
Variables, Vectors, and Matrices
Loops and Functions
Plotting and Graphics
Vectors
Cannot add vectors with size mismatch and/or row and column vectors:
>> x = [1 8 9]; >> y = [1; 8; 9]; >> x + y ??? Error using ==> plus Matrix dimensions must agree.
OK to add/subtract a scalar to/from a vector though:
>> x = [1 8 9]; >> x + 4 ans = 5 12 13
Loops and Functions
Plotting and Graphics
Vectors
To create a row vector (1 × n matrix):
>> x = [1 8 9];