saving multiplications with zeros in a loop

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D_coder 2018-9-13

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/418923-saving-multiplications-with-zeros-in-a-loop

评论： D_coder 2018-9-14

%if true
for i iterations
Matrix = Matrix.*phase %Matrix has lot of zeros I want to skip multiplications with zero. Is it possible to do it in a single line without using if else or any loops
%end

Please dont use sparse, both matrix and phase are two-dimensional array

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采纳的回答

Walter Roberson 2018-9-13

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https://ww2.mathworks.cn/matlabcentral/answers/418923-saving-multiplications-with-zeros-in-a-loop#answer_336733

在 MATLAB Online 中打开

 Mask = Matrix ~= 0;
for i iterations 
  Matrix(mask) = Matrix(mask) * phase ;
end

This assumes that phase is a scalar nonzero value. It does not apply if phase is a vector or 2d array.

If phase is a 2d array then

phases = sparse(phase) ;
Matrix = sparse(Matrix) ;
for i iterations
  Matrix = Matrix * phases;
end

Or better yet,

Matrix = sparse(Matrix) * (phase^iterations) ;

with no loop.

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D_coder 2018-9-14

编辑：Walter Roberson 2018-9-14

actually this code is slow as compared to sparse. And sparse is slower as compared to the normal multiplication.Here is my detailed question. https://www.mathworks.com/matlabcentral/answers/418975-sparse-and-binary-mask

D_coder 2018-9-14