DESCRIPTION

This function get the diagonal part of a matrix.

        csr<Float> a;
        dia<Float> d = diag(a);

TODO

Build a csr matrix from a diagonal one or from a vector:

        dia<Float> d;
        csr<Float> a = diag(d);
        vec<Float> u;
        csr<Float> b = diag(u);

IMPLEMENTATION

template<class T, class M>
dia<T,M> diag (const csr<T,M>& a)