Vandermonde matrix : vandermonde

### 2.41.7 Vandermonde matrix : `vandermonde`

`vandermonde` takes as argument a vector whose components are denoted by xj for j=0..n−1.
`vandermonde` returns the corresponding Vandermonde matrix (the k-th row of the matrix is the vector whose components are xik 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]]`