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

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;

Answer 1

[Matt J]

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