MATLAB: Change specific matrix values to negatives

Question

Hello,

I have two matrices of equal size. One contains negatives and the other does not. I want top convert the values on the positive matrix, that correspond top the negative valus on the other matrix, to negatives. i.e., if: A = [2,1,0,-1,-2,-1,0,1,2]; and B = [4,2,0,2,4,2,0,2,4];

what is the easiest way to make:

B = [4,2,0,-2,-4,-2,0,2,4];

Thanks,

Max

Answer 1

B.*sign(A)

or

(1-(A < 0)*2).*B

or

B(A < 0) = -B(A < 0);