MATLAB Answers

Marie
0

Any tips for bsxfun and repeated calculation?

Asked by Marie
on 29 Oct 2017
Latest activity Commented on by Cedric Wannaz
on 30 Oct 2017
Hello,
I am currently using bsxfun to subtract the first column from matrix A from matrix A itself, which is straightforward. C=bsxfun(@minus,A,B); Say A= [1 2 3; 3 4 1; 1 5 7] and B = [1 3 1]'
I want to do the same for each column and separately stack up the output vertically one matrix after another. In this example, the resulting matrix would thus be:
D= [0 1 2; 0 1 -2; 0 4 6; -1 0 1; -1 0 -3; -4 0 2; -2 -1 0; 2 3 0; -6 -2 0]
Thanks in advance for any advice.

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1 Answer

Answer by Cedric Wannaz
on 29 Oct 2017
Edited by Cedric Wannaz
on 29 Oct 2017
 Accepted Answer

If you have MATLAB R2016b or above, BSXFUN was replaced by automatic expansion and you can do it as follows:
>> D = repmat( A, 3, 1 ) - A(:)
D =
0 1 2
0 1 -2
0 4 6
-1 0 1
-1 0 -3
-4 0 2
-2 -1 0
2 3 0
-6 -2 0
otherwise, almost the same as your first solution:
>> D = bsxfun( @minus, repmat( A, 3, 1 ), A(:) ) ;
Both are based on the fact that indexing A linearly will read it column first:
>> A(:)
ans =
1
3
1
2
4
5
3
1
7

  2 Comments

Thank you for the clear reply; much appreciated!

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