vectorize expression containing if statement
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A = [-5 3 2;2 3 4; 3 5 6; -2 8 9];
%compute product of columns in a vectorized fashion
A(:,1).*A(:,2).*A(:,3);
%calculate the above product only for the rows where the entry in the first column is positive
%solution I do not like. A is not needed anymore after the calculation
A(~(A(:,1)>0),:) = [];
A(:,1).*A(:,2).*A(:,3)
Is there a way to get the above 2x1 result vector using one single line of code? I would also be happy with a 4x1 vector that contains NaN when the condition is not met. The issue is that my real A is quite large in size, so I want to be as efficient as possible and avoiding unnecessary copies or temporary variables related to the condition.
采纳的回答
Here is one way:
A = [-5 3 2;2 3 4; 3 5 6; -2 8 9];
prod(A(A(:,1)>0,:),2)
You could also have done the first operation as
prod(A,2)
2 个评论
SA-W
2023-7-13
the cyclist
2023-7-14
This question is so different from what you oringally asked, that I'm wary of what is important.
Can't you just do
if det(M) > 0
<do the trace operation on M here>
end
?
If that isn't right, can I suggest you post a new question (because what you actually asked here was answered). You can upload your matrix using the paper clip icon in the toolbar, and then people can test code for speed on your actual data.
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