SUBMREDUCE - submatrix reduce

Apply a function to all values in submatrices to return a smaller matrix.

Y = SUBMREDUCE(X,R,C,F) treats the 2D matrix X as consisting of submatrices of RxC rows and columns, and returns a smaller matrix with one value derived from each of these submatrices.
That value is obtained by applying the function pointed to by F to a matrix where the all the submatrix values have been arranged in columns - i.e. the standard syntax for functions such as MIN() and SUM().

Example: if X = [1 2 3 4; 5 6 7 8] then SUBMREDUCE(X,2,2,@sum) = [14 22].