functions:WRAP

example

                     1  2  3  4
 Suppose matrix  M=  5  6  7  8
                     9 10 11 12

 function               result
 -----------------------------------
 WRAP(M,2)              0  5  6  7
                        0  9 10 11
                        1  2  3  4

 WRAP(M,-2)             9 10 11 12
                        2  3  4  0
                        6  7  8  0