Problem 1852. Repeat middle rows and columns of an array

Given an MxN numeric array (A), return an array (B) in which the middle rows and columns have each been repeated once. It may be easier to think of this problem as two operations: (1) repeat the middle rows, and then (2) repeat the middle columns.

The motivation for this problem is to create an array that, when used in blockproc(B,[2 2],fun), effectively incorporates a sliding window with 50% overlap. (NOTE: yes, nlfilter will work on array A, but it requires that the processing output be a scalar, whereas blockproc does not)

You may assume that M>1, N>1 (i.e. no scalars or vectors).

Example

If

A = [1  2  3  4
     5  6  7  8
     9  10 11 12
     13 14 15 16]

Then

B = [1  2  2  3  3  4
     5  6  6  7  7  8
     5  6  6  7  7  8
     9  10 10 11 11 12
     9  10 10 11 11 12
     13 14 14 15 15 16]