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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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0
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0answers
21 views

TensorProduct not working

I am currently trying to get the following to work: ...
2
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1answer
32 views

TensorContract and TensorProduct problem

I am trying the calculate the Kretschmann scalar $K$ of a metric $$K=R^{abcd}R_{abcd}$$ where $R$ is the Riemann tensor. If I do ...
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1answer
34 views

How can I take the divergence of a symbolic vector?

I would like to compute expressions that have the following form: $$\left(\partial_{p_1} - \partial_{p_2}\right)^2 \left(\partial_{p_1} - \partial_{p_2}\right)^2 \frac{(p_1-p_2)\cdot(p_3-p_4)}{p_1^...
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1answer
28 views

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: <...
0
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1answer
55 views

How to flatten a tensor product

Say I have a tensor product of four two dimensional spaces $\Lambda = S\otimes S\otimes S\otimes S$. The basis of $S$ is CB={{1,0},{0,1}} . I generate the ...
3
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1answer
46 views

unexpected `False` for `SymmetricMatrixQ`

Why does the following evaluate to False? ...
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0answers
23 views

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 ...
0
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0answers
17 views

Hamiltonian Analysis in xAct: Variation wrt time derivative of fields

I'd like to use the xAct package to perform the Hamiltonian analysis of a complicated action. To that end, it would be useful to introduce a chart and split indices into "temporal" and "spatial" parts....
4
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1answer
67 views

Reduce memory cost with three matrices multiplication

My program is eating up all my RAM and the operation is related to 3 matrices multiplication, as the code shown below. example code: ...
0
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1answer
42 views

FromTensor + TensorContract gives unexpected result for a tensor product of vectors and a matrix

I have written a larger code that uses the TensorSimplify package written by Carl Woll for tensor manipulations. The code, however, produces unexpected results, ...
-1
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1answer
115 views

Can I numerically solve these equation in Mathematica? [closed]

I have this couple of equations : $ \partial_\mu \partial^\mu z^i + G^{i\bar{p}} (\partial_j G_{k\bar{p}} ) \partial_\mu z^j \partial^\mu z^k + G^{i\bar{j}} (\partial_{\bar{j}} G_{k\bar{l}} ) \...
0
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0answers
40 views

Solving differential forms equations

I have this couple of equations in differential forms language: $ \Delta z^i \star {\bf{1}}+ G^{i\bar{p}} (\partial_j G_{k\bar{p}} ) dz^j \wedge \star dz^k + G^{i\bar{j}} (\partial_{\bar{j}} G_{k\bar{...
0
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0answers
51 views

How to multiply the elements of each site of tensor products to each other while using symbolic representation?

If I have, say three sites in a symbolic operator which is of the form A = a⊗1⊗c and I want it to act on another operator B = a1⊗b⊗1 in order to find the commutator A.B - B....
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0answers
25 views

Contracting the KroneckerDelta should bring it back

I would like to define a function $$V[\phi] = \sum_{1\leq i,j,k,l\leq dim}\lambda_{ijkl} \phi_i\phi_j\phi_k\phi_l, $$ with $\lambda_{ijkl}$ defined by contractions of the type $\delta_{ij}\delta_{kl}$...
2
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0answers
64 views

How to remove the Riemann tensor derivatives using Bianchi identity?

For the third-order Lovelock gravity, after varying the Lagrangian versus the metric, I found some derivatives of the Riemann tensor which should not be appeared. How can I remove them? Maybe using ...
4
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1answer
33 views

Computing Higher Order Tensor of Variable Rank

The following code takes a vector x of variable length, computes the outer product of the vector with itself to form the matrix $\rho$ of dimension $2^n \times 2^n$....
4
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1answer
63 views

How to Creat a Symbolic Rank 4 Symmetric tensor

I would like to create a rank 4 symbolic tensor with this symmetries (1) C_ijkl = C_jikl (2) C_ijkl = C_ijlk (3) C_ijkl = C_klij is there any way to apply symmetry (3)? symmetry (1) and (2) can ...
1
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1answer
40 views

Higher Order Tensor of Variable Rank

I would like to write a function, that matricizes a higher order tensor according to the following rule: Let $\mathcal{A} \in \mathbb{C}^{I_{1} \times I_{2} \times \ldots \times I_{N}}$ be a tensor ...
1
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1answer
44 views

Independent permutation symmetry of a tensor [Using TensorSymmetry command]

Suppose I have this tensor $A_{ijkl} = \epsilon_{ik} \epsilon_{jl}+\epsilon_{il} \epsilon_{jk}$. Now I want to find all the independent permutation symmetries of the indices of this tensor. The answer ...
2
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1answer
72 views

How do I force this simplification?

I am trying to calculate:$$\epsilon_{ijk}n^iM1^j\epsilon^{lmk}n_lM2_m$$ Defining the vectors as: M1={M1x,M1y,M1z} M2={M2x,M2y,M2z} n={nx,ny,nz} and using ...
1
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1answer
57 views

How to define commutative covariant derivatives in xTensor

I'm new with working xAct package and got stuck defining covariant derivatives that commute with each other. I want to simulate flat space-time. And here is my code ...
3
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1answer
52 views

How do I prove this formula with LeviCivitaTensor?

How do I prove that $$ \epsilon_{ijk}\epsilon^{ijm}=2\delta_k^m ? $$ If I use ...
8
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4answers
374 views

How can I automate this tensor computation?

I am doing this work by hand, but it takes a lot of time and I make several calculation errors, so I was thinking to make Mathematica to calculate this for me, but I am stuck at the very beginning. I ...
4
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1answer
98 views

Symbolic multiplication of tensors

I am trying to do symbolic calculations on Pauli Matrix Algebra. I want to find some way of making CircleTimes[a,b] ** CircleTimes[c,d] map to CircleTimes[a.c,b.d] for every a,b,c,d. I would also like ...
6
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1answer
134 views

Speeding up tensor contractions and multiplication

Consider a tensor $T\in\mathbb{R}^{N\times N\times N\times M}$ and two vectors $x,y\in\mathbb{R}^N$. I want to compute the $N\times M$ vector defined by $X_{ij}=\operatorname{tr}(x^\top T_{:,:,i,j}y)=\...
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0answers
33 views

Doubt about tensor producto of two columns vectors

I want to get the tensor product of two columns vectors for example: a={1,2,3} b={2,3,1} psi0 = ArrayFlatten[TensorProduct[a, b]]; The size of psi0 is 3x3 but it ...
0
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0answers
41 views

How to compute gauge variation of expression?

Suppose I have a symmetric tensor field $h_{\mu\nu}$ I want to implement somehow the following gauge variation of this tensor field as follows $\delta h_{\mu\nu} = \nabla_{\mu}\epsilon_{\nu} + \...
1
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0answers
26 views

Inverse fuction of TensorExpand

Is there a way in mathematica to factorize/simplify a dot product? I.e. I have something like a.b + a.c (obviously more complicated expressions) and I would like to factorize terms like ...
10
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2answers
564 views

Make symbols atomic, without losing their type

So, I'd like to define a matrix M, that does not decompose into it's constituents when I do things like Tr[M], but I also want it's type to be retained. (By type, ...
1
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0answers
50 views

Print 4x4x4x4 tensor as 4x4 matrix of 4x4 matrices [closed]

I'd like to print the LeviCivitaTensor[4] tensor as 4x4 block matrix of 4x4 matrices The following code works to display the LeviCivitaTensor[3] tensor as a 3x1 vector of 3x3 matrices. ...
0
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0answers
63 views

CompiledFunction::ctfa - Argument should be a rank 4 tensor of machine-size real number

Dear Mathematica community, I got the following error line: CompiledFunction::ctfa "Argument {<<1>>} at position 1 should be a rank 4 tensor of machine-size real number" This is my function:...
2
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1answer
115 views

xAct, xTensor: How to avoid clash of indices?

Please refer to the picture below. In the first line, I define the angular momentum vector $\vec{L} = \vec{R} \times \vec{P}$ using the Levi-Civita tensor $\epsilon^{i}_{jk}$. The definition relies on ...
3
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0answers
55 views

Lie-algebra valued non-abelian differential forms in Mathematica

I am trying to implement wedge product of Lie-algebra valued differential forms in the non-abelian case. Concretely, I am intereste in 1- and 2-forms, that is, $A$ and $F$. Is there a way of doing ...
2
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1answer
99 views

Outer (dyadic) product between vectors of the same index in two lists

I have two lists of vectors and I want to take the outer product between elements in the lists of the same index. Using either Outer or TensorProduct works for e.g. the first two indices: ...
0
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1answer
32 views

TensorReduce causes “inhomogeneous dimensions” error [closed]

I want to use TensorReduce to realize the following property of wedge: ...
1
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1answer
47 views

How to keep the form of tensor wedge, instead of using tensor product?

Why is an expression with full form of TensorProduct[TensorWedge[v1, v2], w1] changed into ...
2
votes
1answer
69 views

Efficient computation of matrices involving large sums of KroneckerDelta's

I was wondering if one could benefit from Mathematica's rich linear algebra methods for diagonalizing 2nd rank tensors. Namely, in the context of systems (fluids) comprised of capsule-like particles, ...
0
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1answer
107 views

How to construct — based on physics-type notation — a magical simplex $\mathcal{W}$ of bipartite qutrits?

I have a short Mathematica program: ...
2
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1answer
40 views

Maximally expand tensor series?

I am trying to obtain a power series expansion in some real parameter, but all the terms are arbitrary products of tensors. I.e. I want to expand an expression containing sums/products/powers of this ...
2
votes
1answer
57 views

Contraction of square tensors

Let there be tensors A and B A = Outer[Times, {1, 0}, {2, 0}] B = Grad[{f[x, y], g[x, y]}, {x, y}] with output ...
0
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0answers
125 views

How can I define another metric (disformal transformation) in xAct?

I'm using the xAct package. I want to define two metrics with the disformal transformation relation $\qquad \bar{g}_{\mu\nu}=A(\phi) g_{\mu\nu}+B(\phi)\nabla_\mu \phi\nabla_\mu \phi ,$ where $g_{\...
2
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2answers
93 views

How to define an antisymmetric symbol?

I want to work with linear expressions involving the formal symbol $w[a_1,...,a_n]$, and I would like Mathematica to know that expressions such as ...
0
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1answer
44 views

Performing a simple operation with operators [closed]

I have a map defined as $\qquad \Phi(X) = a^2\, Tr[X] |0\rangle \langle 0| + b^2\, Tr[X] |1\rangle \langle 1| + a\,b\, Tr[\sigma_z X] |0\rangle \langle 1| + a\,b\, Tr[\sigma_z X] |1\rangle \langle ...
0
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0answers
43 views

How to save a multidimensional matrix in separated files for each dimension

I need to export to a file a multidimensional matrix, each dimension to a file. For example: ...
0
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1answer
99 views

Exporting a tensor

I have a complicated and large tensor what can be shown in the simplest form as follows How can I export it in this form?
3
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0answers
94 views

Lowering the index of the Riemann curvature tensor in Mathematica

I am looking to do some calculations in GR. For a given metric, I can calculate the affine connection and the Riemann tensor as, ...
1
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1answer
86 views

I want to perform a simple tensorial contraction

I want to perform a simple tensorial contraction like, if KroneckerDelta[i, j] is contracted with some arbitrary tensor A_{lkj} (not-necessarily symmetric) it should give the answer as A_{lki}. Is ...
2
votes
2answers
171 views

How does one plot a 3 dimensional table of numbers?

I've just spent three hours searching the documentation and this website for an answer. I have a rank 3 tensor: t = {{{1, 2}, {3, 4}}, {{5, 6}, {7, 8}}} How ...
0
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1answer
47 views

\[CircleTimes] (tensor symbol use) in infix conversion (solved)

Reformulated problem. I am using the code: ...
20
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4answers
877 views

What is the definition of Curl in Mathematica?

I have a usual mathematical background in vector and tensor calculus. I was trying to use the differential operators of Mathematica, namely Grad, ...