Use two bsxfun for row and column vector to span matrix without putting in memory

Question

T 2017-9-29

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/359070-use-two-bsxfun-for-row-and-column-vector-to-span-matrix-without-putting-in-memory

回答： Jan 2017-9-30

Hello, I have a vector A of size 1xN and a vector B of size MxN I can span a MxN matrix temp with temp=bsxfun(@times,A,B);. Now the tricky part. I create this temp matrix to multiply the following to my data matrix:

data=data.*exp(1i.*temp);

Is there a way I can use bsxfun to directly apply this operation on data, without creating the large temp matrix in the memory?

Thanks

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dpb 2017-9-29

bsxfun created the temp in memory behind scenes anyway, so it didn't actually save memory in computation, just was transparent in not having the explicit temp variable.

Beginning w/ R2016b implicit expansion was introduced that will replace most uses of bsxfun with more efficient memory usage. If you have a release of that vintage or newer investigate that feature.

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Answer 1

Jan 2017-9-30

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/359070-use-two-bsxfun-for-row-and-column-vector-to-span-matrix-without-putting-in-memory#answer_283746

在 MATLAB Online 中打开

A    = rand(1, 1e5);
B    = rand(100, 1e5);
data = ones(size(B));
tic, for k = 1:5
  temp = bsxfun(@times, A, B);
  data = data .* exp(1i .* temp);
end, toc
tic, for k = 1:5
  temp = bsxfun(@times, 1i * A, B);
  data = data .* exp(temp);
end, toc
tic, for k = 1:5
  data = data .* exp((1i * A) .* B);  % Auto-expanding in >= R2016b
end, toc
 Elapsed time is 2.421372 seconds.
 Elapsed time is 2.857152 seconds.
 Elapsed time is 2.136714 seconds.