How can i pull a matrix out of matrix with indices?

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Jiahong Zou
Jiahong Zou 2023-6-16
回答： Matt J 2023-6-16
Hi everyone. Sorry for the poor expression. I used find() function to find elements, which fulfill certain condition (non constant) . I want to have a matrix of same dimension, which contains the rest of elements in Matrix (constant) . Here is my code. But it runs incredibly long, because dimension of thisMatrix{1} is 30000 * 30000 big. How can i do this faster?
Mat_nonconst_tmp = sparse(size(thisMatrix{1}, 1), size(thisMatrix{1}, 2));
for n = 1:length(row_nonconst)
Mat_nonconst_tmp(row_nonconst(n), column_nonconst(n)) = thisMatrix{1}(row_nonconst(n), column_nonconst(n));
end
Mat_const = thisMatrix{1} - Mat_nonconst_tmp;

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采纳的回答

Matt J
Matt J 2023-6-16
Ran in:
Do it a completely different way. Example
A=rand(5)
A = 5×5
0.1956 0.2027 0.4764 0.3016 0.3337 0.6153 0.6513 0.2582 0.3525 0.6252 0.9584 0.8762 0.8876 0.8489 0.0939 0.3990 0.3480 0.6502 0.5263 0.3498 0.6580 0.5777 0.8174 0.1849 0.9899
B=rand(5)
B = 5×5
0.9819 0.5626 0.9978 0.3930 0.7500 0.3371 0.1098 0.4372 0.7146 0.8823 0.2073 0.8749 0.0540 0.1992 0.7296 0.1819 0.4807 0.9508 0.0666 0.0887 0.6023 0.3610 0.9348 0.6361 0.9436
condition=A<0.5;
B(condition)=0
B = 5×5
0 0 0 0 0 0.3371 0.1098 0 0 0.8823 0.2073 0.8749 0.0540 0.1992 0 0 0 0.9508 0.0666 0 0.6023 0.3610 0.9348 0 0.9436

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