A星算法matlab源码及详细注释

% found a better route to it.
else %如果此点在CLOSE表中，说明已经扩展过此点
% find relevant node in CLOSED
I = find(setClosed == posinds(jj));
% a starting position STARTPOSIND, a goal position GOALPOSIND, the costs
% A star will compute movement cost for each tile COSTCHART,
% and a matrix in which to store the pointers FIELDPOINTERS
% update if we have a better route
if setClosedCosts(I) > costs(jj) %如果在CLOSE表中的此点实际代价比现在所得的大（有一个问题，经过此点扩展的点还需要更新当前代价呢!!!）
costchart(setClosed(I)) = costs(jj); %将当前的代价存入costchart中
costchart(posinds(jj)) = costs(jj); %将实际代价值存入对应的costchart中
setOpen = [setOpen; posinds(jj)]; %将此点加入OPEN表中
setOpenCosts = [setOpenCosts; costs(jj)]; %更新OPEN表实际代价
setOpenCosts(I) = costs(jj); %更新OPEN表中的此点代价，注意此点在setOpenCosts中的坐标与在setOpen中是一致的，下同setOpenHeuristics
setOpenHeuristics(I) = heuristics(jj); %更新OPEN表中的此点启发代价(窃以为这个是没有变的)
% keep track of the number of iterations to exit gracefully if no solution
counterIterations = 1;
% create figure so we can witness the magic
axishandle = createFigure(field,costchart,startposind,goalposind);
setOpen = setOpen(1:end-1);
setOpenCosts = setOpenCosts(1:end-1);
setOpenHeuristics = setOpenHeuristics(1:end-1);
end
% for each of these neighbor spaces, assign costs and pointers;
[field, startposind, goalposind, costchart, fieldpointers] = ...
initializeField(n,wallpercent); %初始化界面
% initialize the OPEN and CLOSED sets and their costs
% as long as we have not found the goal or run out of spaces to explore
while ~max(ismember(setOpen,goalposind)) && ~isempty(setOpen) %ismember(A,B)返回与A同大小的矩阵，其中元素1表示A中相应位置的元素在B中也出现，0则是没有出现
setOpen = setOpen(2:end); %temp是OPEN表的第一个元素，删除temp
setOpenCosts = setOpenCosts(2:end);
setOpenHeuristics = setOpenHeuristics(2:end);
else %temp是OPEN表的最后一个元素，删除temp
end
end
end
if isempty(setOpen) break; end %当OPEN表为空，代表可以经过的所有点已经查询完毕
setOpen = [startposind]; setOpenCosts = [0]; setOpenHeuristics = [Inf];
setClosed = []; setClosedCosts = [];
movementdirections = {'R','L','D','U'};
% and if some are in the CLOSED set and their costs are smaller,
% update their costs and pointers
for jj=1:length(posinds) %对于扩展的四个方向的坐标
% put node in CLOSED and record its cost
setClosed = [setClosed; setOpen(ii)]; %将temp插入CLOSE表中
setClosedCosts = [setClosedCosts; setOpenCosts(ii)]; %将temp的花费计入ClosedCosts
ห้องสมุดไป่ตู้ setOpenHeuristics = [setOpenHeuristics; heuristics(jj)]; %更新OPEN表启发代价
% else node has already been seen, so check to see if we have
% found a better route to it.
setClosedCosts(I) = costs(jj); %更新CLOSE表中的此点代价
fieldpointers(setClosed(I)) = movementdirections(jj); %更新此点的方向
end
n = 20; % field size n x n tiles 20*20的界面
wallpercent = 0.45; % this percent of field is walls 45%的界面作为阻碍物（墙）
% create the n x n FIELD with wallpercent walls containing movement costs,
% if cost infinite, then it's a wall, so ignore
if ~isinf(costs(jj)) %如果此点的实际代价不为Inf,也就是没有遇到墙
% if node is not in OPEN or CLOSED then insert into costchart and
if setOpenCosts(I) > costs(jj) %如果在OPEN表中的此点实际代价比现在所得的大
costchart(setOpen(I)) = costs(jj); %将当前的代价存入costchart中，注意此点在costchart中的坐标与其自身坐标是一致的（setOpen(I)其实就是posinds(jj)），下同fieldpointers
% for the element in OPEN with the smallest cost
[temp, ii] = min(setOpenCosts + setOpenHeuristics); %从OPEN表中选择花费最低的点temp,ii是其下标(也就是标号索引)
% find costs and heuristic of moving to neighbor spaces to goal
setOpenCosts = [setOpenCosts(1:ii-1); setOpenCosts(ii+1:end)];
setOpenHeuristics = [setOpenHeuristics(1:ii-1); setOpenHeuristics(ii+1:end)];
elseif (ii == 1)
% update OPEN and their associated costs 更新OPEN表 分为三种情况
if (ii > 1 && ii < length(setOpen)) %temp在OPEN表的中间，删除temp
setOpen = [setOpen(1:ii-1); setOpen(ii+1:end)];
function astardemo
%ASTARDEMO Demonstration of ASTAR algorithm
%
% Copyright Bob L. Sturm, Ph. D., Assistant Professor
% Department of Architecture, Design and Media Technology
% movement pointers, and put node in OPEN
if ~max([setClosed; setOpen] == posinds(jj)) %如果此点不在OPEN表和CLOSE表中
fieldpointers(posinds(jj)) = movementdirections(jj); %将此点的方向存在对应的fieldpointers中
elseif max(setOpen == posinds(jj)) %如果此点在OPEN表中