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xAct Tensor Computer Algebra
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xAct Tensor Computer Algebra
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Manuele Cossari
, …
Jose
6
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
Nils Marion
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 Margalef
2
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 Wardell
4
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 Margalef
2
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-Lahoz
2
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 Bäckdahl
2
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 Bäckdahl
9
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 Nutma
8
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
Rafael Bernar
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
Sukruti
Jun 10
DDI or not
Hello, Given a particular identity for expressions in terms of the Riemann/Ricci tensors and the
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DDI or not
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-Lobo
3
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 Pitrou
3
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 Margalef
3
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 Margalef
2
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 Bäckdahl
2
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 Margalef
4
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 Margalef
2
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 Margalef
2
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
Variationals
I would like to know if X-act support variational manipulations such as:
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Variationals
I would like to know if X-act support variational manipulations such as:
Apr 10
Pavel Petrov
,
Thomas Bäckdahl
4
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
,
Jose
3
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
Giorgos
,
Jose
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
Hermann
,
Jose
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
Joel Feske
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 Bäckdahl
2
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 Margalef
2
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