xCoba: Computing tensor components (with assumptions on second order derivatives)

[Marta Campigotto]

Dear All,

I have just started using xAct, especially for the xCoba package. I found very useful suggestions on this group, but I still have some problems.

I cannot find a way to compute the components of a new defined Tensor. What I'm looking for is a command like MetricCompute but for Tensors defined by me.

I tried with things like //ToBasis[B]//TraceBasisDummy//ToValues but apparently these commands are not meant to be for quantities with free indices. Am I wrong?

Also TensorValues doesn't work.

I also would like to make some assumptions. I would like to tell Mathematica not to consider the second order derivative (covariant) of an arbitrary function.
/. Cd[-a_][Cd[a_] S[x, y, z]] -> 0
Maybe xPert is better for this kind of things?

I attached the notebook. The tensor which I would like to know the components values is G, at the end of the nb.

I am sorry these questions seem stupid, but I couldn't find a solution.
Thank you in advance for answers.

Marta

[Jaswin Kasi]

Hi, 

I am also facing a similar problem, I want to compute the energy-momentum tensor of a scalar field, given a metric. I am able to define the stress tensor, but I am not able to find it's components. Did you find a way to do it ? Could you please help me in finding it ?