You need to find the mean of a 2-D matrix after excluding elements which form an inner sub-matrix. e.g. If the input 2-D matrix A is of size 6x6 and if we want to exclude the elements A(2,2), A(2,3), A(3,2), A(3,3), we just specify r1=1, r2=4, c1=1, c1=4. i.e. we want to exclude elements A(r1+1:r2-1, c1+1:c2-1).