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
采纳的回答
Walter Roberson
2018-9-13
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 个评论
Walter Roberson
2018-9-14
In your revised specifications of 2D matrices and using .* then
mask = Matrix ~= 0; Matrix(mask) = Matrix(mask) .* (phase(mask).^iterations);
This does more multiplications than are strictly necessary if entries in phase can be 0. This code uses two statements; optimizing the multiplications for phase potentially being 0 would require three statements.
Walter Roberson
2018-9-14
There are also optimizations available to reduce the multiplications cost of phase.^iterations but at the potential cost of more memory. These are easiest to code if iterations is a constant. The requirement to use only a single line of code acts against the requirement to reduce multiplications. As I indicated before, if efficiency is the top priority then you should give up on trying to force everything into one line.
D_coder
2018-9-14
编辑：Walter Roberson
2018-9-14
D_coder
2018-9-14
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