xAct Tensor Computer Algebra

Hi, since xPert is specifically desined for curvature based theories, it essentially assumes GR and

I am curious if it's possible to manually specify the components of the inverse metric as an

I am trying to derive expression 19 in This article. First of all I have made setup for field

Hi everyone, I am new to xAct tensor algebra calculator, I have been trying to the field equations of

Hello everyone, Im new to xAct package, can you guys tell me how to define non metricity(Q) and

Hello. First of all, happy 2025 to everyone. I am using the following line item in my worksheet,

Dear all, Following this question I am trying to define the derivative of the inverse. Something like

Hi! The first problem comes from the output of Tex@PDNP[{1, -NP}][PsiCD1[]] which is "\Psi _{1}{

Hi all, I've been banging my head against this problem for some time now, so I would appreciate

Thanks!! I will try with this On Thu, Dec 19, 2024, 7:05 PM Thomas Bäckdahl <thomas.backdahl@gmail

Good morning (in my time zone). I am trying to compute a dispersion relation for curvature

I am trying to figure out how one is able to get the components of metric and Christoffel symbols in

Dear xAct users, We are happy to announce the release of TInvar, a new package for canonicalization

Hi! It is easier to help if you send notebooks instead of pictures, but this was short so it's

Hello all, In the documentation file of xCoba, it is saying that the part related to the computations

Hi all, For a metric which is parametrized as follows, g[0,0]= - Exp[phi] g[0,i]=A[i] Exp[phi] g[i,0]

Thank you very much, Ilham, for your help. I will carefully analyze what you wrote to me. El jueves,

You can use SortCovDs in the definition when doing the perturbation before doing ToCanonical Collect[

Apologies for my mistake, in the previous email I attached the wrong file. I am now attaching the

Hi, Can anyone recommend me a way to extract components from a row matrix when using xCoba? My code

Hello, I have a list of terms in which a couple of them have the same index structure and they differ

Hi, Thanks for creating that mirror, Konstantinos. Something has changed again in the xact.es domain

Hey ! How to do it with a tensor field and not a scalar field ? Le lundi 22 juillet 2024 à 10:41:16

Hello, I need to compute the canonical momenta associated to the metric components. I want to

Dear Armando, After two days of confusion this indeed resolved the problem. Compared with your

Hello, When defining a rule using EqToRule, is it possible to add a condition for the rule to work?

Hello! I am new to xPert as well as xAct, and I have a simple question: DefManifold[M, 4, {a, b, c, d

Hi Thomas, Thank you very much for your reply! It has been very helpful. I have two questions.

Hello everyone, I am fairly new to Mathematica and xAct and were not able to find my answers in the

Hello everyone. This is my first post in this community. I am learning some features of xAct,