Circular Matrix computation

Commodity function for building a circulant matrix given a vector

circulant Computes the circulant matrix of a vector.

circulant(vec) is a max(size(vec))-by-max(size(vec)) circulant
matrix built with the elements of vec

Note: The parameter may be either a column or row vector

Example:
v = [ 1 2 3 4 ];
circulant( v )

ans =

1 2 3 4
2 3 4 1
3 4 1 2
4 1 2 3