# Questions tagged [xact]

Questions about xAct, a suite of packages for tensor computer algebra, which includes the packages xCore, xPerm, xTensor, and xCoba.

123 questions
Filter by
Sorted by
Tagged with
17 views

### Tensors without explicit specifications in xCoba

In the standard Schwarzschild setup I have the following tensor: ...
27 views

### Specify a tensor or a function with a specific form in xCoba [closed]

Suppose, in the Schwarzschild geometry with the standard coordinates, I wanted to specify an electromagnetic tensor F with the (six) components all being functions of r: A(r), B(r), C(r), D(r), G(r), ...
1 vote
103 views

### Using Reduce to simplify (not solve) system of equations

I'm dealing with a Mathematica program that generates a set of coupled non-linear equations involving an unknown function and its derivatives with respect to at least one independent variable. My goal ...
1 vote
34 views

### functional derivative with respect to the partial derivative of the metric with xAct

I want to compute the functional derivative with respect to a partial derivative of the metric with the mathematica package xAct. This is what I have tried so far: ...
70 views

234 views

### Substitution rule is not working

I'm trying to replicate the equations of motion of the $4\partial$ST theory in Mathematica as is done in here as I need to use Mathematica and this package for my thesis. However, I have some trouble ...
1 vote
52 views

50 views

### in xAct, simplify output expression by specfic the form a function with ReplaceAll or Simplify

in xAct, at the beginning I define a function H1(t,r) that depends on two variables using the command DefScalarFunction, then I want to simplify an output ...
1 vote
221 views

### xAct: How to identify and split module dummy indices?

Hi I'm using the package xAct but I'm running into an issue. It seems that before using //ChristoffelToGradMetric the christoffel connection has indices (which can ...
1 vote
167 views

180 views

### Commutation of the partial derivatives on scalar in xAct

I do not know how to automatically commute partial derivatives on a scalar and simplify it. For example, if I have: $$\partial_a \partial_b \partial_c f- \partial_c \partial_a \partial_b f$$ where $f$...
133 views

### Symbolic representation of large output

The package xAct does something really nice when it handles large outputs, which is to represent the expression as a symbol and display that symbol when the cursor hovers over it. For example, ...
158 views

39 views

### "Uncaught Throw[Null]","VBundleOfMetric" and "MetricsOfVBundle" when using package "xAct"

The codes are below: Remove["Global*"] Then: ...
284 views

### Manipulating tensorial terms with xAct, ToCanonical is not perfoming well

I am trying to calculate perturbations of some complicated Lagrangians. Using xAct and more specifically VarD to perform the perturbations the expressions become ...
166 views

### Not able to impose rules on xPert perturbations

Whenever I try to define rules to xPert perturbations, they seem not to work at all. For instance, I am interested in considering traceless and divergence-free perturbations and defining ...
1 vote