EXPAND

Replicate and tile each element of an array.

Description

EXPAND(A,SZ), for array A and vector SZ replicates each element of A by SZ. The results are tiled into an array in the same order as the elements of A, so that the result is size: size(A).*SZ.

Therefore the number of elements of SZ must equal the number of dimensions of A, or in MATLAB syntax:

length(size(A))==length(SZ)

must be true.
The result will have the same number of dimensions as does A.
There is no restriction on the number of dimensions for input A.

Examples:

>> A = [1 2;3 4]
A =
     1 2
     3 4
>> expand(A,[2 1])
ans =
     1 2
     1 2
     3 4
     3 4
>> expand(A,[2 2])
ans =
     1 1 2 2
     1 1 2 2
     3 3 4 4
     3 3 4 4

Please email me if bugs are found in the code. Thanks.

Acknowledgements

The author wishes to acknowledge the following in the creation of this submission:
REPLICATE

• MATLAB release: MATLAB 7.4 (R2007a)
• Other Files: expand.m, ; license.txt

[Jos (10584)]

Why not simply
kron(A,eyes(SZ))

or, for non-numerical arrays,
X = {'a' 'b' ; [1:3] []}
X(kron(reshape(1:numel(X),size(X)), ones(2,3)))
%ans =
% 'a' 'a' 'a' 'b' 'b' 'b'
% 'a' 'a' 'a' 'b' 'b' 'b'
% [1x3 double] [1x3 double] [1x3 double] [] [] []
% [1x3 double] [1x3 double] [1x3 double] [] [] []

It can be expanded to the ND case using reshape etc ...

Good help though!

[Matt Fig]

Hello Jos,

There are a couple of reasons I bypassed kron. The main reason is that expand, even with error checking etc., is faster on my machine(s):

A = reshape(randperm(24),6,4);
SZ = [300,400];
tic
T = expand(A,SZ);
toc %Elapsed time is 0.043622 seconds.
tic
T2 = kron(A,ones(SZ));
toc %Elapsed time is 0.082535 seconds.

For
A = reshape(randperm(144),18,8);
SZ = [300,400];
expand is .25 vs. .78 seconds for kron. 2007b win xp.

expand also works for your second example.
Thanks.

[us]

just like jos, i also felt at first that this - admittedly sleek engine - was more or less a KRON clone; but then your timing convinced me that there was clearly more to it...
however, i think you should at least mention KRON in a
see also:
statement...
us

[Matt Fig]

Another reason I bypassed kron is illustrated here:

http://i217.photobucket.com/albums/cc229/spamanon/tester_output-2.png

Urs, I think you are correct about mentioning kron in the see also.