Re: Help with matrix replication

[Laurent Hoeltgen]

On 20/12/12 17:50, Richardson, Anthony wrote:
> 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
>
>
>
>
>
>
>
>
> 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
>
>
>
> _______________________________________________
> Help-octave mailing list
> address@hidden
> https://mailman.cae.wisc.edu/listinfo/help-octave

Hi,

try

kron(a,[1 1 ; 1 1])

for your case n=2. kron is the Kronecker Matrix product.

Regards,
Laurent