First argument of MatrixElement should be a matrix

Raise code

            if n.is_Integer and m.is_Integer:
                return name[n, m]
        if isinstance(name, str):
            name = Symbol(name)
        else:
            name = _sympify(name)
            if not isinstance(name.kind, MatrixKind):
                raise TypeError("First argument of MatrixElement should be a matrix")
        obj = Expr.__new__(cls, name, n, m)
        return obj

    def doit(self, **kwargs):
        deep = kwargs.get('deep', True)
        if deep:
            args = [arg.doit(**kwargs) for arg in self.args]