xAct Tensor Computer Algebra

Hi everyone, I am pretty new to xAct, so maybe this question is really simple. I'm doing a

Hello everyone 😁 I had the same error and I fixed it using: (*Arreglo del problema 13.+ *) (*1.

I solved it now with the usual xPert method and replacing the variation of the matter Lagrangian by

Hey everyone, As you will see in the attached notebook. I'm trying to generate some DDIs using

Hi, Is there any way to work with metric variation in arbitrary d dimension? I have been looking into

First notice that //. rules apply "rules" repeatedly until there are no more possible

Here is the revised notebook. I did some corrections and got some equations. But I think there is

Could anyone please help me to find find functional derivative of some expression in using Xact

Hi, Oh I see, FreeIndsDown[] is not supposed to sort the indices. In that case, both functions are

Hi! This is a name conflict with new functions in Mathematica 14.3. José should soon release a new

Hi, I am trying to perturbed Einstein equation for Schwarzschild background metric, essentiality want

Hi, Thank you for the command suggestions! They work as needed and give the desired output. I think

Hi, I have made a small notebook which explains how to obtain perturbation equations in a synchronous

Hi I am not sure I understand what you want. Is your dX factor fixed? You have defined it as a 1-form

Thank you Juan, it works fine. суббота, 30 августа 2025 г. в 22:53:44 UTC-3, Juan Margalef: As a

One can, if one wishes, remove the "quarantine" attribute from the current version of xPerm

Hi Thomas Bäckdahl, I really appreciate your reply. I used the following: DefConstantSymbol[dim,

Hi I added into your file here "approach 3" which contains my answer. The modified file is

Hi All, Now that Wolfram Language 14.3 has been released, I'd like to upload a new version of

Hi! All of these things are manifestations of evaluation control in Mathematica. If you write

I am glad!! Just for future reference, what I did was to take the file xPert.nb, look for

Hello guys, I'm trying to derive the modified Tolman-Oppenheimer-Volkoff (TOV) equations for a

In my xAct project using Mathematica, I encountered an issue while constructing a 4×4 matrix using

Hi Barry, Thank you for your reply. If possible, I'd like to sign up for a notification in case

Thank you for your help. Have a nice day Il ven 11 lug 2025, 13:13 Jose <jo...@xact.es> ha

Hi everyone, I am using Cyril Pitrou's ActionVariation_Metric_Fields.nb on xAct-contrib/examples

Hi Alejandro. It is hard to check your notebook since it is not selfcontained, try to add all the

Hi , Just to add that TInvar (like Invar before it) only knows about the Bianchi identity for the

Changing the definition might be too complicated and have unexpected consequences. I would recommend

Hello! I realise that this is an old question but I recently tried to tackle the same problem so I