Computing expressions in terms of Christoffel symbols

[Alice Crafford]

Hi there, 

I think this may be a pretty basic question, but I'm a bit stuck and could use a hand ! 

I'm working with a non-diagonal metric that contains several arbitrary functions of r, and I've used xAct & xCoba to compute the Christoffel symbols, Riemann tensor, Ricci scalar, etc. in terms of these. I need to compute several expressions that depend on various Christoffel symbols, and I want to substitute in their explicit forms in a particular coordinate basis. I haven't been able to figure out how to do this ; I suspect you can do it with a rule but I'm not sure how. 

For example I've defined a coordinate basis which I called cb, and the input 

ChristoffelCDPDcb[{0, cb}, {2, -cb}, {2, -cb}] 

results in 

Gamma[Nabla, D]^{t}_{\theta \theta} , 

instead of the expression for Gamma^{t}_{\theta \theta} in terms of (derivatives of) metric components, which I've obtained earlier in my code. I'm a bit stuck because I haven't had this issue with any other objects so far. 

If someone could suggest a fix that would be awesome ! 

Thanks a lot, 

- AC 

[Juan Margalef]

Hi AC,

We would need a bit more information to help you. Provide a minimal working example of the code where the problem appears so that we can understand better the problem and help you find a solution.

Best,

Juan