# Matrix addition only to elements equal to zero

4 views (last 30 days)
Albin on 20 Nov 2023
Edited: Albin on 20 Nov 2023
Hi!
I would like to perform a matrix addition, i.e C=A+B.
However, I want this addition to be performed only for the elements in matrix B that is zero, for all non-zero elements of matrix B the addition should not be performed.
Obviously, this could be done - certainly not beautifully - with an if statement in a loop over all the elements in matrix B. However, I wonder if there is a more neat and faster solution to do this? Especially because my matrices are of size (256,256,329) which makes this solution quite slow.
And for clarity, here is my proposed but unsatisfactory solution:
for i=1:numel(reg_nolower)
if reg_nolower(i) == 0
reg_nolower(i)=reg_nolower(i)+reg_leftarm(i)+reg_rightarm(i);
else
end
end
##### 2 CommentsShow NoneHide None
Bruno Luong on 20 Nov 2023
Your code doesn't not reflect your description : your test is on reg_nolower which is the resultant not the reg_leftarm or reg_rightarm, and which is A, B and C in that ?
Albin on 20 Nov 2023
Edited: Albin on 20 Nov 2023
Right, sorry. My description was thought of as a general formulation of the problem. Applied on my problem, it would be an addition as D=A+B+C; where reg_nolower is C where the addition shall be performed only if the elements are equal to zero. And A and B are the matrices containing the arms.
I apologize for the confusion.

Bruno Luong on 20 Nov 2023
C=B;
B0 = B==0;
C(B0)=A(B0);

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