# Questions tagged [tensors]

Use this tag for questions that involve tensors. Tensors are fundamental tools for linear computations, generalizing vectors and matrices to higher ranks. Mathematica 9 introduces powerful methods to algebraically manipulate tensors with any rank and symmetry.

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### How to make an inverse operation to KroneckerProduct[A, IdentityMatrix[m]] (simplify matrix)?

The operation KroneckerProduct[A, IdentityMatrix[m]] expands the matrix A in the following way (depending on order of ...
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### Doing ArrayReshape in Mathematica doesn't give desired results

I have an array like this for example, a = ArrayReshape[Range, {4, 4}] \begin{align} \left( \begin{array}{cccc} 1 & 2 & 3 & 4 \\ 5 & 6 & ...
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### Output of expressions unable to have operations be performed on the expression

I am currently trying to use the code linked in the catalog of spacetimes pdf to calculate chirstoffel symbols for a metric which follows as n := 4 ...
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### Create a tensor with a well defined symmetry

I want to create a symmetric rank four tensor with this kind of symmetry: {1,2} and {3,4}. How can I implement this using "Array"? ...
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### How to compute the divergence of a four-vector?

I have a quadri-vector which is given by u = {(E^(-φ0[r]))*(1 - ε δφ[t, r]), (E^(-φ0[r])) D[ε ξ[t, r], t], 0, 0} and a quantity n which is given by <...
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### Mathematica: Partial derivative with respect to tensors

Anyone know how to do the partial derivative of a tensor in d dimensions on Mathematica ? I want to implement something which will calculate directly like that :
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### How to compute the covariant derivative of a vector? [duplicate]

I want to compute a derivative of a vector, but I'm new to mathematica (I programmed in other languages). I was advised to work with the diffgeo.m package. What I want to do is calculate using ...
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### How to sum over a two tensor with a simple constraint of the form $i<j$?

I am trying to write a sum of the form $$\sum_{i<j}f_{ij}$$ where $i,j\in \{1,2,3,4\}.$ I want to write something like Sum[f[[i,j]], {j,1,4},{i,1,j}] but then ...