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# Nested For Loop for 2D Matrix

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BBB on 11 Nov 2019
Commented: Matt J on 11 Nov 2019
I want to create a nested for loop that essentially goes through a 2D matrix of 600x1000 dimensions, such that in every loop in both of the dimensions it picks out exactly 51x51 part of the 2D matrix in either of the dimensions and multiplies it to another 51x51 separate matrix.
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### Accepted Answer

Matt J on 11 Nov 2019
Edited: Matt J on 11 Nov 2019
So then you want to extract random 51x51 submatrices? If so, then,
I=sort(randperm(600,51));
J=sort(randperm(1000,51));
submatrix= matrix(I,J);
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Matt J on 11 Nov 2019
Is it element-wise multiplication, or another kind? And what is to be done with each of the 51x51 multiplication results? In double floating point, this will require 10 GB of storage if they are kept simultaneously in memory,
>> (600-51)*(1000-51)*51^2*8/2^30
ans =
10.0965

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### More Answers (1)

Matt J on 11 Nov 2019
I vaguely wonder whether you are just re-inventing convolution
result = conv2(Matrix,staticMatrix,'valid');
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