Help with matrix replication

[Richardson, Anthony]

I want to duplicate the rows in a matrix n times and then duplicate the columns n times.

 

For example, if

 

a =

 

     1.0000e+00     2.0000e+00     3.0000e+00

     4.0000e+00     5.0000e+00     6.0000e+00

 

for n= 2, I want

 

b =

 

     1.0000e+00     1.0000e+00     2.0000e+00     2.0000e+00     3.0000e+00     3.0000e+00

     1.0000e+00     1.0000e+00     2.0000e+00     2.0000e+00     3.0000e+00     3.0000e+00

     4.0000e+00     4.0000e+00     5.0000e+00     5.0000e+00     6.0000e+00     6.0000e+00

     4.0000e+00     4.0000e+00     5.0000e+00     5.0000e+00     6.0000e+00     6.0000e+00

 

Note that this is not matrix replication(it is equivalent to using simple pixel replication to zoom in on an image matrix).  I thought I would be able to avoid loops by using some combination or repmat/repelems/reshape, but the best I could come up with was:

 

b = reshape(repmat(reshape(repelems(a, [1:numel(a); n(ones(1,numel(a)))])',n*rows(a),columns(a)),n,1),n*rows(a),n*columns(a));

 

After studying the “advanced indexing” section of the manual I came up with a more syntactically elegant (it does not appear to be any more time-efficient) solution:

 

b = a((1:rows(a))(ones(1,n),:), (1:columns(a))(ones(1,n),:));

 

I still feel as if I’m overlooking some simple method for doing what I want to do.  Does anyone have a better method?

 

By the way, imresize(a, 2, ‘nearest’) will do what I want, but this is a function from the image package and I’m trying to write some routines that duplicate the functionality of the image package without using any of those functions.

Thanks

Tony Richardson