How do I subtract every row of a matrix with every row of a second matrix?

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Paola
Paola on 25 Oct 2021
Commented: Paola on 26 Oct 2021
Hi,
I have two matrices A (26 rows X 5100 columns) and B (26rows X 5100 columns) and I want to subtract every row of A with every row of B to obtain another matric C (2601 rows X 5100 columns). How can I have the matrix C?

Accepted Answer

ChrisR
ChrisR on 25 Oct 2021
Here's how I understood the question. If you have A = magic(3) and B = eye(3)--that is,
A = [8 1 6; 3 5 7; 4 9 2];
B = [1 0 0; 0 1 0; 0 0 1];
then you can subtract the rows of B from each row of A with
m = size(A,1);
C = repelem(A,m,1) - repmat(B,m,1);
This approach gives
C = [7 1 6; 8 0 6; 8 1 5; 2 5 7; 3 4 7; 3 5 6; 3 9 2; 4 8 2; 4 9 1];
But in the example given in the question, this approach would produce a 676x5100 matrix, not a 2601x5100 matrix.
  1 Comment
Paola
Paola on 26 Oct 2021
Thank you vary much Chris,
it worked perfectly. And yes sorry my matrices were 51X5100 not 26X5100.
Thanks

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