Any tips for bsxfun and repeated calculation?

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.

Answer 1

[Cedric]

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

[Marie]

Thank you for the clear reply; much appreciated!

[Cedric]

My pleasure!