Vandermonde matrix : vandermonde

vandermonde takes as argument a vector whose components are denoted by x_j for j = 0..n - 1.
vandermonde returns the corresponding Vandermonde matrix (the k-th row of the matrix is the vector whose components are x_i^k for i = 0..n - 1 and k = 0..n - 1).
Warning !
The indices of the rows and columns begin at 0 with Xcas.
Input :

vandermonde([a,2,3])

Output (if a is symbolic else purge(a)) :

[[1,1,1],[a,2,3],[a*a,4,9]]