A square matrix, in which each row is a circular shift of the preceding row
and the first row is a circular shift of the last row, is called circulant matrix.
Example:
he(o) he(M-1) he(M-2)………… he(1)
he(1) he(0) he(M-1)………. he(2)
.
.
he(M-1) he(M-2) he(M-3)………. he(0)
