'Cartan matrix of Lie algebra associated with this root system
Examples
>>> from sympy.liealgebras.root_system import RootSystem
>>> c = RootSystem("A3")
>>> c.cartan_matrix()
Matrix([
[ 2, -1,  0],
[-1,  2, -1],
[ 0, -1,  2]])'

def cartan_matrix(self):

    return self.cartan_type.cartan_matrix()
