# Questions tagged [xact]

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

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### 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 ...
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1 vote
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### 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 $f$...
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### 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, ...
1 vote
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### Kretschmann scalar in xTensor and xCoba

How do I calculate the Kretschmann scalar $K=R_{abcd}R^{abcd}$ with xTensor and xCoba? I have found the functions Kretschmann and ...
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### How to work with Levi civita tensor in xAxt?

Is there any command to work with the Levici vita tensor? In fact, I found LeviCivitaTensor, however, in calculations it doesn't seem practical. see the example: <...
1 vote
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### Derivatives with dummy indices not commutative after 3d derivative?

Recently I've encountered the following issue in xAct. I've defined the Manifold and tensors in the following manner Then consider the following expressions. In the case where there are 2 ...
1 vote
Let's sayI have the following expression in xAct where covariant derivatives are commutative, $\epsilon$ and $h$ are symmetric tensors. As we can see this expression is equivalent to If we ...