speed up the & operation

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Chaoyang Jiang 2018-4-12

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https://ww2.mathworks.cn/matlabcentral/answers/394421-speed-up-the-operation

评论： Walter Roberson 2018-4-13

How to speed up the following code? I did profiling, and this line takes 3267.72s for calling 245913489 times.

a=[1 0 1 1 0 1 1 1 1 1 0 0 1 1 0 1 1 1 0 1 1 0 1 1 1 0 1 1 0 1 1 1];
b=[1 0 1 1 0 1 1 1 1 1 0 0 1 1 0 1 1 1 0 1 1 0 1 1 1 0 1 1 0 1 1 1  1 1 1 1 1 0 0 1 1 0 1 1 1 0 1 1 0 1 1 1 0];
for i=1:1000000
aat=((a(1,1:24)==0)&(b(1,25:48)==1)&(~ismembc(1:24,5:50)))';
end

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Chaoyang Jiang 2018-4-13

ismembc seems to be faster than ismember, that is why I used this function.

Walter Roberson 2018-4-13

在 MATLAB Online 中打开

for i=1:1000000
  part1 = a(1,1:24)==0;
  part2 = b(1,25:48)==1;
  part3 = ~ismembc(1:24,5:50);
  part4 = part1 & part2 & part3;
  aat = part4 .';
end

Now when you profile you can see exactly which part of the expression is taking the most time.

We suspect that it is the ismembc() that is taking all of the time and that the & is relatively fast.

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