xCoba does not calculate tensors with MetricCompute

[Albin Nilsson]

I have followed the example in KerrNewmanExamples.nb and tried to set up a similar environment for my metric. 

I have a spherically symmetric spacetime containing arbitrary functions:

MatrixForm[Metric = {
{-Exp[-2r Phi[r]], 0,0,0},
{0,1/(1-b(r)/r), 0,0},
{0,0,r^2,0},
{0,0,0,r^2 Sin[Theta]^2}
}]

and I am trying to calculate all the tensors using MetricCompute: (I have followed all the steps in the example, defined coordinate chart CC, manifold etc. If I copy the metric from the example to my code, it works)

MetricCompute[Metric, CC, All, CVsimplify -> Simplify]

This command gives the following output:

** DefTensor: Defining weight +2 density DetmetricCC[]. Determinant.
** DefTensor: Defining tensor ChristoffelCDPDCC[a,-b,-c].

and nothing else. If I run

MetricCompute[metric,CC,"Riemann"[-1,-1,-1,-1],CVSimplify-> Simplify]

nothing at all happens.

Does anyone have any idea as to what is going on?

Thanks in advance!

[Jose]

Hi,

Note that in xCoba the metric field must be given in terms of coordinate fields, so you need to express Metric in terms of the scalar field r[], and not just r. Try changing r to r[] and Theta to Theta[] in the definition of Metric.

Note you also need to declare b and Phi using DefScalarFunction.

In general, it is always a better idea to send full code for a minimal example that reproduces the problem, so that we can run it.

Cheers,

Jose.

[Albin Nilsson]

Hi, 

this solved the problem, thanks!