int cg(const Matrix &A, Vector &x, const Vector2 &Mb, const Preconditioner &M, const solver_option &sopt=solver_option())
field residue(Float p, const field &uh)
int gmres(const Matrix &A, Vector &x, const Vector &b, const Preconditioner &M, SmallMatrix &H, const SmallVector &V, const solver_option &sopt=solver_option())