Relativity using Mathematica

Hello,
I would like to be able to get Mathematica do the long calculations necessary in Einstein’s Relativity.
For example, if I define a metric , what is the command needed to work out the Christoffel symbols ? Having done that, what is the command to work out the components of the Riemann tensor ?

All help is gratefully received .

Cheers,

Andy.

Refer to Wolfram Library Resources on relativity