MATLAB bsxfun 或矢量化

Question

我一直在努力使用bsxfun对我的代码进行矢量化，但我遇到了一个我无法完全破解的场景。 这是问题的一个小样本。 我想删除此代码中的 for 循环，但我很难使用 tempEA 行。

Index = [2; 3; 4;];
dTime = [25; 26; 27; 28; 25; 26; 27; 28; 27; 28];
dIndex = [3; 3; 3; 2; 1; 3; 2; 4; 4; 2];
aTime = [30; 38; 34; 39; 30; 38; 34; 39; 34; 39];
aIndex = [4; 2; 5; 4; 5; 4; 4; 2; 2; 4];
EA = zeros(numel(Index));
for i = 1:numel(Index)
    for j = 1:numel(Index)
        tempEA = aTime(Index(i) == dIndex(:,1) & Index(j) == aIndex(:,1));
        if i == j
        elseif tempEA > 0
            EA(i,j) = min(tempEA);
        else
            EA(i,j) = 50;
        end
    end
end

答案应如下所示：

EA =
     0    50    34
    38     0    30
    34    50     0

提前感谢您的帮助。

Answer 1

这使用 bsxfun ; 没有循环。它假定您的aTime值中没有NaN 。

N = numel(Index);
ii = bsxfun(@eq, dIndex.', Index); %'// selected values according to each i
jj = bsxfun(@eq, aIndex.', Index); %'// selected values according to each j
[ igrid jgrid ] = ndgrid(1:N); %// generate all combinations of i and j
match = double(ii(igrid(:),:) & jj(jgrid(:),:)); %// each row contains the matches for an (i,j) combination
match(~match) = NaN; %// these entries will not be considered when minimizing
result = min(bsxfun(@times, aTime, match.')); %'// minimize according to each row of "match"
result = reshape(result,[N N]);
result(isnan(result)) = 50; %// set NaN to 50
result(result<=0) = 50; %// set nonpositive values to 50
result(1:N+1:end) = 0; %// set diagonal to 0

仅当aTime可以包含非正值时，才需要行result(result<=0) = 50;。可以吗？或者您的elseif tempEA > 0只是检查tempEA是否为空的一种方式？