saving multiplications with zeros in a loop

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%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

Accepted Answer

Walter Roberson
Walter Roberson on 13 Sep 2018
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.
  4 Comments
D_coder
D_coder on 14 Sep 2018
Edited: Walter Roberson on 14 Sep 2018
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
D_coder on 14 Sep 2018
Hey Walter my top priority is speed and saving multiplications.

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