cartanMatrix -- Provide the Cartan matrix of a simple Lie algebra

Description

i1 : g=simpleLieAlgebra("G",2)

o1 = g

o1 : simple LieAlgebra

i2 : cartanMatrix g

o2 = | 2  -1 |
     | -3 2  |

              2       2
o2 : Matrix ZZ  <-- ZZ