Groups

xAct Tensor Computer Algebra

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Manuele Cossari, … Jose6

11:53 AM

Installation problems

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

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Installation problems

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

11:53 AM

Jul 9

Variational derivative of the vielbein determinant with FieldsX

Hello xAct Community! I am currently working on a project allowing to compute EOM of IIA /IIB Sugra.

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Variational derivative of the vielbein determinant with FieldsX

Hello xAct Community! I am currently working on a project allowing to compute EOM of IIA /IIB Sugra.

Jul 9

Yusuf Emre BARAN

Jul 5

Defining the spin tensor using the matter Lagrangian

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

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Defining the spin tensor using the matter Lagrangian

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

Jul 5

Alejandro Aguilar, Juan Margalef2

Jul 4

Help obtaining correct equations of motion

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

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Help obtaining correct equations of motion

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

Jul 4

Michael Seifert, … Barry Wardell4

Jul 3

Automating d^2 A = 0 in xTensor language

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

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Automating d^2 A = 0 in xTensor language

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

Jul 3

Yusuf Emre BARAN, Juan Margalef2

Jun 30

Changing the definition of the Riemann and the torsion tensors

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

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Changing the definition of the Riemann and the torsion tensors

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

Jun 30

Theo, Sergi Sirera-Lahoz2

Jun 20

Including anisotropic stress in xPand

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

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Including anisotropic stress in xPand

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

Jun 20

ali khaled, Thomas Bäckdahl2

Jun 18

Factorising a tensor outside of an expression

Hi! If the name of your tensor is JJ, you can try things like Collect[ScreenDollarIndices[%], {JJ[__]

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Factorising a tensor outside of an expression

Hi! If the name of your tensor is JJ, you can try things like Collect[ScreenDollarIndices[%], {JJ[__]

Jun 18

Sukruti, … Thomas Bäckdahl9

Jun 16

MakeRule with Conditions

Hi! First of all it is PairQ, not Pair. Secondly, as I said, you should not use conditions in

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MakeRule with Conditions

Hi! First of all it is PairQ, not Pair. Secondly, as I said, you should not use conditions in

Jun 16

Sukruti, … Teake Nutma8

Jun 11

Identity missing in TInvar?

Dear Teake, Thank you for your reply. You said "For the particular case in the Gauss-Bonnet

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Identity missing in TInvar?

Dear Teake, Thank you for your reply. You said "For the particular case in the Gauss-Bonnet

Jun 11

Jun 10

Christoffel symbols between two parallel derivatives

Hello, I am trying to compute the partial derivatives, in a given chart S, of the basis vectors from

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Christoffel symbols between two parallel derivatives

Hello, I am trying to compute the partial derivatives, in a given chart S, of the basis vectors from

Jun 10

Jun 10

Hello, Given a particular identity for expressions in terms of the Riemann/Ricci tensors and the

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Hello, Given a particular identity for expressions in terms of the Riemann/Ricci tensors and the

Jun 10

João Vitor Santos Perles

May 20

[xAct] Help with correct index factorization in Lagrangian with symmetric rank-3 tensor

Dear colleagues, how are you? We are working with a symmetric rank-3 tensor field, h_{\mu\nu\rho},

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[xAct] Help with correct index factorization in Lagrangian with symmetric rank-3 tensor

Dear colleagues, how are you? We are working with a symmetric rank-3 tensor field, h_{\mu\nu\rho},

May 20

Max Banados, Alfonso García-Parrado Gómez-Lobo3

May 19

xTerior: trouble with component-tensor-valued forms

Thanks Alfonso, indeed it did work. Regards, Max On Monday, May 19, 2025 at 10:48:43 AM UTC-4 Alfonso

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xTerior: trouble with component-tensor-valued forms

Thanks Alfonso, indeed it did work. Regards, Max On Monday, May 19, 2025 at 10:48:43 AM UTC-4 Alfonso

May 19

Abhishek Hegde K R, Cyril Pitrou3

May 9

Xact provides inconsistent answers with 3+1 decomposition

Ah, I see. Thank you very much for catching the mistake. I do have a follow up question on this now.

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Xact provides inconsistent answers with 3+1 decomposition

Ah, I see. Thank you very much for catching the mistake. I do have a follow up question on this now.

May 9

Augniva Ray, Juan Margalef3

May 3

Explicit result of inner contractions : Code " Int" in xTerior package

Hi Juan, this works wonderfully. Thanks. Also, thanks for the plausible clarification as to why it

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Explicit result of inner contractions : Code " Int" in xTerior package

Hi Juan, this works wonderfully. Thanks. Also, thanks for the plausible clarification as to why it

May 3

Alejandro Aguilar

Apr 29

Help with obtaining EoM for Dynamical Chern-Simons

Hi everyone, I'm having trouble with obtaining the equations of motion for DCS theory. According

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Help with obtaining EoM for Dynamical Chern-Simons

Hi everyone, I'm having trouble with obtaining the equations of motion for DCS theory. According

Apr 29

Eran Lavi, Juan Margalef2

Apr 28

Request for assistance

Hi Eran. I am afraid there are several mistakes. 1. The use of components requires the package xCoba.

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Request for assistance

Hi Eran. I am afraid there are several mistakes. 1. The use of components requires the package xCoba.

Apr 28

Elias Leite Mendonça, Thomas Bäckdahl2

Apr 26

Tensor symmetric in a pair of indices and under the chage of pairs

Hi! You don't have to use just symmetric, or antisymmetric groups. You can specify any list of

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Tensor symmetric in a pair of indices and under the chage of pairs

Hi! You don't have to use just symmetric, or antisymmetric groups. You can specify any list of

Apr 26

Andrew Kovachik, Juan Margalef4

Apr 22

Confusing behaviour of ToBasis

Hi Andrew, I recommend that you read the xCoba documentation carefully to understand the issue you

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Confusing behaviour of ToBasis

Hi Andrew, I recommend that you read the xCoba documentation carefully to understand the issue you

Apr 22

Yerlan Myrzakulov, Juan Margalef2

Apr 11

Help with xAct Error in R^2 Model Variation Calculation

Hi Yerlan, You need to define ALL the objects appearing in the Lagrangian: DefTensor[\[Phi][], M4]

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Help with xAct Error in R^2 Model Variation Calculation

Hi Yerlan, You need to define ALL the objects appearing in the Lagrangian: DefTensor[\[Phi][], M4]

Apr 11

SHIVAM SINGH KUSHWAH, Juan Margalef2

Apr 11

Wrong results in Variation of action

Hi Shivam, The short answer to your first two questions is that you need to use something additional,

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Wrong results in Variation of action

Hi Shivam, The short answer to your first two questions is that you need to use something additional,

Apr 11

Henrique Yuiti Fukushima Komada

Apr 10

I would like to know if X-act support variational manipulations such as:

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I would like to know if X-act support variational manipulations such as:

Apr 10

Pavel Petrov, Thomas Bäckdahl4

Apr 6

How can we show that the tensor expression is identically zero?

Hi! It is difficult to see from pictures what is going on. There could be something that I have fixed

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How can we show that the tensor expression is identically zero?

Hi! It is difficult to see from pictures what is going on. There could be something that I have fixed

Apr 6

Marco Schreck, Jose3

Apr 3

Problem with permutation routine when using xTensor/xCoba

Dear José, thank you very much for your reply and for looking into this. Indeed, things work out when

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Problem with permutation routine when using xTensor/xCoba

Dear José, thank you very much for your reply and for looking into this. Indeed, things work out when

Apr 3

Apr 2

ToCanonical seems to abort

Your proposed solution worked. Thanks! My expression simplified significantly (way less than 1000

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ToCanonical seems to abort

Your proposed solution worked. Thanks! My expression simplified significantly (way less than 1000

Apr 2

Mar 29

Christoffel symbols in xTensor symbolically

Hi Hermann, Before we discuss how to implement it, we need to discuss what it is that you want to do.

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Christoffel symbols in xTensor symbolically

Hi Hermann, Before we discuss how to implement it, we need to discuss what it is that you want to do.

Mar 29

Mar 22

Defining related charts

Hi, I'm wondering if there is a way to define charts whose scalar functions are explicitly

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Defining related charts

Hi, I'm wondering if there is a way to define charts whose scalar functions are explicitly

Mar 22

Henrique Yuiti Fukushima Komada, Thomas Bäckdahl2

Mar 22

Help with Levi-Civita symbol

Hi! Try the following: PrintAs[epsilonmetric]^="\[Epsilon]" Regards Thomas On 2025-03-22 07

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Help with Levi-Civita symbol

Hi! Try the following: PrintAs[epsilonmetric]^="\[Epsilon]" Regards Thomas On 2025-03-22 07

Mar 22

Gabriel Sánchez Pérez, Juan Margalef2

Mar 20

Declare that the zeroth order in a expansion is zero

The problem is that Perturbation[B[_],0] returns B[_] and when you make the rule to put that to zero,

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Declare that the zeroth order in a expansion is zero

The problem is that Perturbation[B[_],0] returns B[_] and when you make the rule to put that to zero,

Mar 20

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