Returns the circular matrix
A = makematrix_circul ( x )
a n-by-1 or 1-by-n matrix of doubles, the input vector
a n-by-n matrix of doubles, the circular matrix
Returns the circular matrix of size n with entries x.
A circulant matrix is a special kind of Toeplitz matrix where each row vector is rotated one element to the right relative to the preceding row vector.
http://en.wikipedia.org/wiki/Circulant_matrix