# I want to fix the zeros values in their same indices in certain two matrices A and B (to not be updated) in a cost function?

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M on 17 Sep 2022
Edited: Voss on 17 Sep 2022
I want to build a cost function, I want to fix the zeros values in their same indices in certain two matrices A and B (to not be updated) .
for example this is matrix A:
A = [ 0.1 0.2 0
0.2 0.8 0
0 0 0.7 ]
and I want to update this matrix by some computions, but I want to keep the zero values in their same indices and not update them.
Is there any sugestion to do that?
and in general is there a method to fix values in their same indices ( I mean do the calculation on the all values in this matrix but dont change these values; in my case the zero values)

Voss on 17 Sep 2022
Edited: Voss on 17 Sep 2022
A = [0.1 0.2 0; 0.2 0.8 0; 0 0 0.7]
A = 3×3
0.1000 0.2000 0 0.2000 0.8000 0 0 0 0.7000
newA = [1 2 3; 4 5 6; 7 8 9]
newA = 3×3
1 2 3 4 5 6 7 8 9
idx = A == 0;
A(~idx) = newA(~idx)
A = 3×3
1 2 0 4 5 0 0 0 9