Evaluating xTensor expressions for a given metric using xCoba

[Quim Llorens Giralt]

Hi everyone,

I have some long abstract expressions that I have computed using xTensor.
Now, I would like to evaluate them using xCoba in some particular metrics (like AdS, Schw, etc) without having to rewrite them again.

Is there a function that evaluates an abstract expression given a particular metric in xCoba? I'm sure there is, but I haven't easily found it and I'm getting confused because sometimes xAct doesn't know which metric to use (either the abstract or the particular one).

I attach an easy example.

Thanks in advance!
Quim

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[jose xact.es]

Hi,

Yes, this functionality has been requested a number of times. The thing to do is to write a list of rules replacing the abstract objects by the respective component tensors, which can be done by hand to be specific about which tensors are needed. But I understand it can be automated. So I've written a simple function doing this at the end of your notebook. If this is not enough, send another example with something that doesn't work.

Cheers,

Jose.

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From: xa...@googlegroups.com <xa...@googlegroups.com> on behalf of Quim Llorens Giralt <qllo...@icc.ub.edu>
Sent: Thursday, September 30, 2021 6:04 AM
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Subject: [xAct] Evaluating xTensor expressions for a given metric using xCoba

 

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[Quim Llorens Giralt]

Thank you very much!
This is exactly what I was looking for.

Quim

[徐涌群]

Hi

Jose did a great job!

And I throuth I have a naive edition of this, about ansatz compont evaluation. It was mentioned a lot in this group.

I was try to get equation 5 in the paper:[2009.00512v2] Tensor Perturbations and Thick Branes in Higher-dimensional $f(R)$ Gravity (arxiv.org)

 

My code in attached below. Hope it may help 

Best regard

Yongqun Xu 

[Jose]

Hi,

I reattach your notebook with the computation I think you want.

I must say that I generally don't look at computations that involve comparing with articles, because it usually takes much time, but this case was relatively clear.

Cheers,

Jose.

On Wednesday, October 6, 2021 at 3:26:24 PM UTC-5 phy...@gmail.com wrote:

Hi

Jose really did a great job! He has posed several reply about ansatz compont evaluation. I have learned a lot form them.

And now I have a easier edition of this. I was trying to get equation 5 in the paper:[2009.00512v2] Tensor Perturbations and Thick Branes in Higher-dimensional $f(R)$ Gravity (arxiv.org)

 

My code in attached below. Hope it may help 

Best regards

Yongqun Xu

在2021年10月5日星期二 UTC+8 上午12:29:20<qllo...@icc.ub.edu> 写道：