# Index Matrix A and Matrix B Problems

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jane on 24 Jun 2022
Edited: Dhritishman on 3 Jul 2022
i have matrix A and Matrix B
A = [[ 0, 1, 1, 0, 1, 0,1],
[ 0, 0, 1, 1, 0, 0,0],
[ 1, 1, 0, 1, 1, 0,0]],
B = [[ 234, 59, 15, 99, 61, 74 ,71],
[ 16, 27, 14, 13, 111, 345.67],
[ 54, 23, 16, 14, 13, 27,100]],
How to make the value in matrix B be 0 if the value in matrix A is 1.
For example, in matrix A (row 1, column 2), the value of 1 in matrix B (row 1, column 2) will be 0.
I tried using loop but it didn't work. Thank you

James Tursa on 24 Jun 2022
Edited: James Tursa on 24 Jun 2022
You can use logical indexing:
B(A==1) = 0;
You can use a loop for this also, but you would have to show us the code you used before we can tell you what you did wrong with that approach.
jane on 24 Jun 2022
Thanks James

Voss on 24 Jun 2022
A = [ 0, 1, 1, 0, 1, 0,1; 0, 0, 1, 1, 0, 0,0; 1, 1, 0, 1, 1, 0,0]
A = 3×7
0 1 1 0 1 0 1 0 0 1 1 0 0 0 1 1 0 1 1 0 0
B = [ 234, 59, 15, 99, 61, 74 ,71; 16, 27, 14, 13, 111, 345,67; 54, 23, 16, 14, 13, 27,100]
B = 3×7
234 59 15 99 61 74 71 16 27 14 13 111 345 67 54 23 16 14 13 27 100
B(A == 1) = 0
B = 3×7
234 0 0 99 0 74 0 16 27 0 0 111 345 67 0 0 16 0 0 27 100
Voss on 24 Jun 2022
You're welcome!

Dhritishman on 3 Jul 2022
Edited: Dhritishman on 3 Jul 2022
MATLAB provides logical indexing which can be used to select or modify elements of a matrix.
A = [0, 1, 1, 0, 1, 0, 1; 0, 0, 1, 1, 0, 0,0; 1, 1, 0, 1, 1, 0,0]
A = 3×7
0 1 1 0 1 0 1 0 0 1 1 0 0 0 1 1 0 1 1 0 0
B = [234, 59, 15, 99, 61, 74, 71; 16, 27, 14, 13, 111, 345, 67; 54, 23, 16, 14, 13, 27, 100]
B = 3×7
234 59 15 99 61 74 71 16 27 14 13 111 345 67 54 23 16 14 13 27 100
% This line of code changes the value in matrix B to 0 if the value of the corresponding element in matrix A is 1.
B(A == 1) = 0
B = 3×7
234 0 0 99 0 74 0 16 27 0 0 111 345 67 0 0 16 0 0 27 100

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