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Matrix column subtraction problem

Asked by Jakub Nosek on 11 Mar 2018
Latest activity Commented on by Jakub Nosek on 11 Mar 2018
I know this is really basic stuff but unfortunately I can't get to the right solution.
I have for example these 2 matrices:
matrixA=[1 5;5 2;0 0;3 2;3 6]
and
matrixB=[4 5 6;8 5 2;3 3 2;1 2 1;2 5 4]
What I want to do is to subtract all columns in matrixB from column 1 and column 2 respectively in matrixA. So I want to make
matrixC=[1-4 1-5 1-6 5-4 5-5 5-6;5-8 5-5 5-2 2-8 2-5 2-2;....;....;.....]

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2 Answers

Answer by Roger Stafford on 11 Mar 2018
Edited by Roger Stafford on 11 Mar 2018
 Accepted Answer

C = zeros(5,2*3);
for p = 1:2
for q = 1:3
C(:,3*p+q-3) = A(:,p)-B(:,q);
end
end
Or this:
C = reshape(repmat(reshape(A,5,1,2),1,3,1)-repmat(reshape(B,5,3,1),1,1,2),5,[]);

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You can use 3D indexing for your assignment, and reshape() afterwards.
@Jakub: For matrices A and B of general size:
[m,n1] = size(A);
n2 = size(B,2); % size(B,1) must also be m
C = reshape(repmat(reshape(A,m,1,n1),1,n2,1)-repmat(reshape(B,m,n2,1),1,1,n1),m,[]);
Thanks!

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Answer by Walter Roberson
on 11 Mar 2018

[matrixA(:,1)-matrixB,matrixA(:,2)-matrixB]
This might require R2016b or later.

  2 Comments

Thanks, is there any other solution for older versions of MATLAB?
cell2mat(arrayfun(@(COLIDX) bsxfun(@minus, matrixA(:,COLIDX), matrixB), 1:size(matrixA,2), 'uniform', 0))

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