# How i fix the error "Matrix dimensions must agree?"

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zahra banoori on 22 Jul 2021
Answered: Image Analyst on 23 Jul 2021
xi=randi([10,30],4,4)
A=xi(1,:)
B=xi(:,1)
C=A - B
Why i get matrix dimensions must agree error.

Chunru on 23 Jul 2021
Which version of matlab you are using?
xi=randi([10,30],4,4)
xi = 4×4
13 17 21 15 14 12 14 11 13 28 28 16 20 14 24 25
A=xi(1,:)
A = 1×4
13 17 21 15
B=xi(:,1)
B = 4×1
13 14 13 20
% arrays with implicit expansion for newer matlab
% both A and B are expanded into compatible size before operation
C = A - B
C = 4×4
0 4 8 2 -1 3 7 1 0 4 8 2 -7 -3 1 -5
DGM on 23 Jul 2021
IIRC, the generalized implicit expansion is R2016b and later. Prior to that, you can use bsxfun()
xi=randi([10,30],4,4);
A = xi(1,:);
B = xi(:,1);
C1 = A - B % R2016b and later
C1 = 4×4
0 6 5 -1 -11 -5 -6 -12 -13 -7 -8 -14 -13 -7 -8 -14
C2 = bsxfun(@minus,A,B) % R2007a and later
C2 = 4×4
0 6 5 -1 -11 -5 -6 -12 -13 -7 -8 -14 -13 -7 -8 -14

Image Analyst on 23 Jul 2021
Not sure what you want or are expecting because you forgot to tell us. Perhaps you want a 1-dimensional, 4-element vector. If so, here is how to do it.
xi = randi([10, 30], 4, 4) % 4-by-4 matrix.
A = xi(1, :) % Row vector
B = xi(:, 1) % Column vector
C1 = A(:) - B(:) % C will be a column vector.
C2 = A - B' % C will be a column vector.
C1 =
0
-7
-16
2
C2 =
0 -7 -16 2
If you want a 2-D matrix, then C=A-B works with no error in recent versions of MATLAB that do implicit expansion. But you also forgot to list your release when you posted. Here is another chance to read the posting guidelines and edit your post to improve it: