Carview!

4 votes

1 answer

111 views

Combining exterior derivatives with endomorphisms

(I am a Mathematica novice, please be gentle) I am trying to perform an explicit but lengthy tensor computation and from what I can tell the xterior.m package has much of the functionality I need but ...

Thisquestionisreallyhard

141

asked Jul 14 at 18:32

4 votes

3 answers

184 views

Canonical way to handle alternating tensors? Basis construction

Is there a canonical way to construct alternating tensors in mathematica? I have tried several different ways of constructing a basis for alternating tensors. However, all options seem rather clunky. ...

EEH

146

asked Jun 19 at 20:12

0 votes

0 answers

43 views

xAct -- Metric perturbation by Ricci tensor

I want to compute the perturbed Ricci scalar $\overline{R}$ to second order in $\epsilon$ when the metric $g_{ab}$ is perturbed by $\epsilon R_{ab}$, where $\epsilon$ is a constant parameter. I tried ...

physmath17

1

asked May 26 at 12:04

1 vote

0 answers

55 views

Transpose function fails to give a correct result [closed]

Mathematica 12.3.1.0 Platform: Linux x86 (64bit) I have a tensor ten Dimension[ten] ...

Tom

131

asked May 23 at 9:31

1 vote

0 answers

62 views

How to calculate the perturbation for Ricci scalar squared

Consider a perturbation for this metric: $$ ds^2= \left(g_{\alpha\beta}+ \delta g_{\alpha\beta} \right) dx^\alpha dx^\beta , $$ in the form: \begin{eqnarray} \delta g_{00}&=&- a^2(\tau)\left( ...

Dr. phy

447

asked Mar 24 at 10:01

3 votes

2 answers

145 views

How to make tensor product linear

Is it possible to define certain variable as scalars with respect to the tensor product? Say, I have abstract tensors A, B, C and scalar coefficients a, b, c. When I apply ...

VladM

305

asked Mar 21 at 15:31

4 votes

0 answers

104 views

Simple MatrixSymbol and Solve example in 14.2

I'm excited about the new symbolic tensor features. I'm trying to just do some simple linear algebra with the least squares regression formula for some 2D data points. Initializing: ...

Michael Hale

2,373

asked Mar 8 at 1:45

1 vote

1 answer

69 views

Using xAct to calculate contractions of the torsion tensor in terms of its irreducible components

I'm fairly new to Mathematica, and especially xAct. Before I state the question, some background: In Einstein-Cartan theory, the torsion tensor is assumed to be non-vanishing (unlike General ...

Yaezir

11

asked Mar 3 at 23:52

0 votes

0 answers

67 views

Using indices to define the metric and Ricci tensor

This question is related to a previous thread Calculating the covariant derivative of Ricci scalar. I try to write MA code to define a new modified Einstein tensor: $$ G'_{\mu\nu} = G_{\mu\nu}- \frac{...

Dr. phy

447

asked Mar 2 at 11:55

1 vote

0 answers

121 views

Calculating the covariant derivative of Ricci scalar

I use the following code to calculate the Einstein tensor. Now I'm trying to add new terms to the Einstein tensor: $ G'_{\mu\nu} = G_{\mu\nu}- \frac{1}{3} \left[ \left( \frac{1}{4} R^2 + \nabla_\...

Dr. phy

447

asked Feb 26 at 14:01

3 votes

0 answers

100 views

Differentiating an inactive indexed sum returns 0 in Wolfram 14.2

I recently encountered unexpected behavior when computing the derivative of an inactive indexed sum in Wolfram 14.2.0. This example is taken directly from the official documentation of ...

Pei-Xin Shen

103

asked Feb 1 at 14:44

1 vote

0 answers

33 views

double derivative in xTensor package

I am starting with xTensor package (being the subpackage of xAct). I defined simple tensors and tried to evaluate a second covariant derivative on the scalar function as follows ...

nabzdyczony

111

asked Jan 15 at 12:06

1 vote

0 answers

42 views

Symmetric CP and Tucker/HOSVD decompositions of symmetric tensors

When Taylor expanding a multivariable function, we end up with symmetric tensors $A_{1,...,N}$ for the $N$'th order polynomial. Under certain smoothness conditions for the function, the tensor $A$ is ...

Hmecher

11

asked Jan 9 at 16:43

8 votes

1 answer

198 views

Simplifying an expression containing NonThreadable + Dot gives unexpected result?

Bug introduced in 14.1 202412 Consider this example vec//Attributes={NonThreadable}; expr={a,b} . ({c,d}+vec); expr//Simplify expr//Distribute//Simplify ...

Lacia

3,128

asked Dec 8, 2024 at 19:34

1 vote

0 answers

57 views

How to Substitute a Metric into a Variation of the Action in Mathematica to Obtain Field Equations?

I have already calculated the variation of an action for a modified gravitational theory, and now I want to substitute a specific metric (e.g., the Schwarzschild metric) into this variation in ...

Elena Margalejo

11

asked Nov 8, 2024 at 23:17

Stack Exchange Network

Questions tagged [tensors]

Combining exterior derivatives with endomorphisms

Canonical way to handle alternating tensors? Basis construction

xAct -- Metric perturbation by Ricci tensor

Transpose function fails to give a correct result [closed]

How to calculate the perturbation for Ricci scalar squared

How to make tensor product linear

Simple MatrixSymbol and Solve example in 14.2

Using xAct to calculate contractions of the torsion tensor in terms of its irreducible components

Using indices to define the metric and Ricci tensor

Calculating the covariant derivative of Ricci scalar

Differentiating an inactive indexed sum returns 0 in Wolfram 14.2

double derivative in xTensor package

Symmetric CP and Tucker/HOSVD decompositions of symmetric tensors

Simplifying an expression containing NonThreadable + Dot gives unexpected result?

How to Substitute a Metric into a Variation of the Action in Mathematica to Obtain Field Equations?

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Questions tagged [tensors]

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