Tensor[InvariantTensorsAtAPoint] - find tensors or differential forms which are invariant under the infinitesimal action of a set of matrices
Calling Sequences
InvariantTensorsAtAPoint(A, S, options)
Parameters
A - a list of square matrices, with dimension equal to the dimension of the space on which the tensors S are defined
S - a list of tensors or differential forms, each of the same index type
options - the keyword argument output
Description
Examples
This command calculates the tensors in the span of the tensors in the list S which are invariant with respect to the infinitesimal action generated by the matrices in the list A. This is a pointwise calculation.
Let x1, x2, ... xn be the coordinates in terms of which the tensors in the list S are defined. If P = pji and X= Xi ∂i , then PX= − pj i Xj ∂i . If α = ai dx i , then Pα= pj i aj dxi . If T1 and T2 are tensors, then PT1 ⊗ T2 = PT1 ⊗ T2 + T1 ⊗P T2. Thus, the action of P on a tensor T defined at a point coincides with the Lie derivative of T (as a tensor with constant coefficients) with respect to the linear vector field ZP = pj i xj ∂i ,that is, P T = LZPT. See Example 6 for examples of this action of matrices on tensors.
If A = P1 , P2 , ... , Pn and S = T1 , T2 , ... , Tm, then InvariantTensorsAtAPoint(A, S) returns a basis for the vector space of all tensors T = t1T1 + t2T2 + .. . + tmTm (ti constant) such that P1T = P2T =. . .= PmT = 0.
If no invariant tensors exist, an empty list is returned.
With output = "list", a list of invariant tensors is returned. This is the default. With output = "general", a single tensor with arbitrary coefficients _C1 , _C2 , ... is returned. If the number of matrices in the list A is 1 and output = "action", then the action of the matrix in A on the tensors in S is returned.
In many cases, the list of tensors S to be used by InvariantTensorsAtAPoint can be created with the commands GenerateTensors, GenerateSymmetricTensors, GenerateForms.
with⁡DifferentialGeometry:with⁡Tensor:with⁡LieAlgebras:with⁡GroupActions:
Example 1.
Define a list of matrices for the first argument of InvariantTensorsAtAPoint .
A ≔ Matrix⁡1,0,0,−1,Matrix⁡0,1,0,0
Define a 2-dimensional space on which the tensors S for the second argument of InvariantTensorsAtAPoint will be defined.
DGsetup⁡x,y,M
frame name: M
We take for S the space of all rank 2 covariant tensors on M.
S ≔ evalDG⁡dx &t dx,dx &t dy,dy &t dx,dy &t dy
_DG⁡tensor,M,cov_bas,cov_bas,,1,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,2,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,2,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,2,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,2,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,2,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,2,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,2,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,2,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,2,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,2,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,2,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,2,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,2,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,2,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,2,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,2,1
InvariantTensorsAtAPoint⁡A,S
_DG⁡tensor,M,cov_bas,cov_bas,,1,2,−1,2,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,2,−1,2,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,2,−1,2,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,2,−1,2,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,2,−1,2,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,2,−1,2,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,2,−1,2,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,2,−1,2,1,1
Example 2.
Here we consider a simple example where the matrices A depend upon the coordinates of the manifold on which the tensors S are defined.
DGsetup⁡x,y,z,M
A ≔ Matrix⁡0,1,0,−1,0,0,0,0,0,Matrix⁡0,0,1,0,0,0,−1y2,0,0,Matrix⁡0,0,0,0,0,1,0,−1y2,0
We take for S the space of all symmetric rank-2 covariant tensors on M.
S ≔ evalDG⁡dx &t dx,dx &s dy,dx &t dz,dy &t dy,dy &s dz,dz &t dz
_DG⁡tensor,M,cov_bas,cov_bas,,1,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,2,12,2,1,12,_DG⁡tensor,M,cov_bas,cov_bas,,1,3,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,2,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,3,12,3,2,12,_DG⁡tensor,M,cov_bas,cov_bas,,3,3,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,2,12,2,1,12,_DG⁡tensor,M,cov_bas,cov_bas,,1,3,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,2,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,3,12,3,2,12,_DG⁡tensor,M,cov_bas,cov_bas,,3,3,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,2,12,2,1,12,_DG⁡tensor,M,cov_bas,cov_bas,,1,3,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,2,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,3,12,3,2,12,_DG⁡tensor,M,cov_bas,cov_bas,,3,3,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,2,12,2,1,12,_DG⁡tensor,M,cov_bas,cov_bas,,1,3,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,2,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,3,12,3,2,12,_DG⁡tensor,M,cov_bas,cov_bas,,3,3,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,2,12,2,1,12,_DG⁡tensor,M,cov_bas,cov_bas,,1,3,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,2,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,3,12,3,2,12,_DG⁡tensor,M,cov_bas,cov_bas,,3,3,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,2,12,2,1,12,_DG⁡tensor,M,cov_bas,cov_bas,,1,3,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,2,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,3,12,3,2,12,_DG⁡tensor,M,cov_bas,cov_bas,,3,3,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,2,12,2,1,12,_DG⁡tensor,M,cov_bas,cov_bas,,1,3,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,2,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,3,12,3,2,12,_DG⁡tensor,M,cov_bas,cov_bas,,3,3,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,1,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,2,12,2,1,12,_DG⁡tensor,M,cov_bas,cov_bas,,1,3,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,2,1,_DG⁡tensor,M,cov_bas,cov_bas,,2,3,12,3,2,12,_DG⁡tensor,M,cov_bas,cov_bas,,3,3,1
We find that the A-invariant tensors vary with the coordinate y.
_DG⁡tensor,M,cov_bas,cov_bas,,1,1,1y2,2,2,1y2,3,3,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,1,1y2,2,2,1y2,3,3,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,1,1y2,2,2,1y2,3,3,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,1,1y2,2,2,1y2,3,3,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,1,1y2,2,2,1y2,3,3,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,1,1y2,2,2,1y2,3,3,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,1,1y2,2,2,1y2,3,3,1,_DG⁡tensor,M,cov_bas,cov_bas,,1,1,1y2,2,2,1y2,3,3,1
Example 3.
The classical simple Lie algebras can be defined as matrix algebras which leave a tensor or a collection of tensors invariant. In this example we check that the 4 ×4 matrices defining the real sympletic algebra leave invariant a non-degenerate 2-form.
We first use the commands SimpleLieAlgebraData and StandardRepresentation to obtain the matrices defining sp4, R.
LD ≔ SimpleLieAlgebraData⁡sp(4, R),sp4R
_DG⁡LieAlgebra,sp4R,10,table( [( "rank" ) = [2], ( "algebratype" ) = "spnR", ( "vectortable" ) = table( [( "A" ) = table( [( [2, 2] ) = 4, ( [2, 1] ) = 3, ( [1, 1] ) = 1, ( [1, 2] ) = 2 ] ), ( "B" ) = table( [( [2, 4] ) = 7, ( [1, 4] ) = 6, ( [1, 3] ) = 5 ] ), ( "C" ) = table( [( [4, 2] ) = 10, ( [3, 1] ) = 8, ( [3, 2] ) = 9 ] ) ] ), ( "representationdimension" ) = 4, ( "IndTable" ) = [["A", [1, 1], [[[1, 1], 1], [[3, 3], -1]]], ["A", [1, 2], [[[1, 2], 1], [[4, 3], -1]]], ["A", [2, 1], [[[2, 1], 1], [[3, 4], -1]]], ["A", [2, 2], [[[2, 2], 1], [[4, 4], -1]]], ["B", [1, 3], [[[1, 3], 1]]], ["B", [1, 4], [[[1, 4], 1], [[2, 3], 1]]], ["B", [2, 4], [[[2, 4], 1]]], ["C", [3, 1], [[[3, 1], 1]]], ["C", [3, 2], [[[3, 2], 1], [[4, 1], 1]]], ["C", [4, 2], [[[4, 2], 1]]]] ] ),1,2,2,1,1,3,3,−1,1,5,5,2,1,6,6,1,1,8,8,−2,1,9,9,−1,2,3,1,1,2,3,4,−1,2,4,2,1,2,6,5,2,2,7,6,1,2,8,9,−1,2,9,10,−2,3,4,3,−1,3,5,6,1,3,6,7,2,3,9,8,−2,3,10,9,−1,4,6,6,1,4,7,7,2,4,9,9,−1,4,10,10,−2,5,8,1,1,5,9,2,1,6,8,3,1,6,9,1,1,6,9,4,1,6,10,2,1,7,9,3,1,7,10,4,1,_DG⁡LieAlgebra,sp4R,10,table( [( "rank" ) = [2], ( "algebratype" ) = "spnR", ( "vectortable" ) = table( [( "A" ) = table( [( [2, 2] ) = 4, ( [2, 1] ) = 3, ( [1, 1] ) = 1, ( [1, 2] ) = 2 ] ), ( "B" ) = table( [( [2, 4] ) = 7, ( [1, 4] ) = 6, ( [1, 3] ) = 5 ] ), ( "C" ) = table( [( [4, 2] ) = 10, ( [3, 1] ) = 8, ( [3, 2] ) = 9 ] ) ] ), ( "representationdimension" ) = 4, ( "IndTable" ) = [["A", [1, 1], [[[1, 1], 1], [[3, 3], -1]]], ["A", [1, 2], [[[1, 2], 1], [[4, 3], -1]]], ["A", [2, 1], [[[2, 1], 1], [[3, 4], -1]]], ["A", [2, 2], [[[2, 2], 1], [[4, 4], -1]]], ["B", [1, 3], [[[1, 3], 1]]], ["B", [1, 4], [[[1, 4], 1], [[2, 3], 1]]], ["B", [2, 4], [[[2, 4], 1]]], ["C", [3, 1], [[[3, 1], 1]]], ["C", [3, 2], [[[3, 2], 1], [[4, 1], 1]]], ["C", [4, 2], [[[4, 2], 1]]]] ] ),1,2,2,1,1,3,3,−1,1,5,5,2,1,6,6,1,1,8,8,−2,1,9,9,−1,2,3,1,1,2,3,4,−1,2,4,2,1,2,6,5,2,2,7,6,1,2,8,9,−1,2,9,10,−2,3,4,3,−1,3,5,6,1,3,6,7,2,3,9,8,−2,3,10,9,−1,4,6,6,1,4,7,7,2,4,9,9,−1,4,10,10,−2,5,8,1,1,5,9,2,1,6,8,3,1,6,9,1,1,6,9,4,1,6,10,2,1,7,9,3,1,7,10,4,1,_DG⁡LieAlgebra,sp4R,10,table( [( "rank" ) = [2], ( "algebratype" ) = "spnR", ( "vectortable" ) = table( [( "A" ) = table( [( [2, 2] ) = 4, ( [2, 1] ) = 3, ( [1, 1] ) = 1, ( [1, 2] ) = 2 ] ), ( "B" ) = table( [( [2, 4] ) = 7, ( [1, 4] ) = 6, ( [1, 3] ) = 5 ] ), ( "C" ) = table( [( [4, 2] ) = 10, ( [3, 1] ) = 8, ( [3, 2] ) = 9 ] ) ] ), ( "representationdimension" ) = 4, ( "IndTable" ) = [["A", [1, 1], [[[1, 1], 1], [[3, 3], -1]]], ["A", [1, 2], [[[1, 2], 1], [[4, 3], -1]]], ["A", [2, 1], [[[2, 1], 1], [[3, 4], -1]]], ["A", [2, 2], [[[2, 2], 1], [[4, 4], -1]]], ["B", [1, 3], [[[1, 3], 1]]], ["B", [1, 4], [[[1, 4], 1], [[2, 3], 1]]], ["B", [2, 4], [[[2, 4], 1]]], ["C", [3, 1], [[[3, 1], 1]]], ["C", [3, 2], [[[3, 2], 1], [[4, 1], 1]]], ["C", [4, 2], [[[4, 2], 1]]]] ] ),1,2,2,1,1,3,3,−1,1,5,5,2,1,6,6,1,1,8,8,−2,1,9,9,−1,2,3,1,1,2,3,4,−1,2,4,2,1,2,6,5,2,2,7,6,1,2,8,9,−1,2,9,10,−2,3,4,3,−1,3,5,6,1,3,6,7,2,3,9,8,−2,3,10,9,−1,4,6,6,1,4,7,7,2,4,9,9,−1,4,10,10,−2,5,8,1,1,5,9,2,1,6,8,3,1,6,9,1,1,6,9,4,1,6,10,2,1,7,9,3,1,7,10,4,1,_DG⁡LieAlgebra,sp4R,10,table( [( "rank" ) = [2], ( "algebratype" ) = "spnR", ( "vectortable" ) = table( [( "A" ) = table( [( [2, 2] ) = 4, ( [2, 1] ) = 3, ( [1, 1] ) = 1, ( [1, 2] ) = 2 ] ), ( "B" ) = table( [( [2, 4] ) = 7, ( [1, 4] ) = 6, ( [1, 3] ) = 5 ] ), ( "C" ) = table( [( [4, 2] ) = 10, ( [3, 1] ) = 8, ( [3, 2] ) = 9 ] ) ] ), ( "representationdimension" ) = 4, ( "IndTable" ) = [["A", [1, 1], [[[1, 1], 1], [[3, 3], -1]]], ["A", [1, 2], [[[1, 2], 1], [[4, 3], -1]]], ["A", [2, 1], [[[2, 1], 1], [[3, 4], -1]]], ["A", [2, 2], [[[2, 2], 1], [[4, 4], -1]]], ["B", [1, 3], [[[1, 3], 1]]], ["B", [1, 4], [[[1, 4], 1], [[2, 3], 1]]], ["B", [2, 4], [[[2, 4], 1]]], ["C", [3, 1], [[[3, 1], 1]]], ["C", [3, 2], [[[3, 2], 1], [[4, 1], 1]]], ["C", [4, 2], [[[4, 2], 1]]]] ] ),1,2,2,1,1,3,3,−1,1,5,5,2,1,6,6,1,1,8,8,−2,1,9,9,−1,2,3,1,1,2,3,4,−1,2,4,2,1,2,6,5,2,2,7,6,1,2,8,9,−1,2,9,10,−2,3,4,3,−1,3,5,6,1,3,6,7,2,3,9,8,−2,3,10,9,−1,4,6,6,1,4,7,7,2,4,9,9,−1,4,10,10,−2,5,8,1,1,5,9,2,1,6,8,3,1,6,9,1,1,6,9,4,1,6,10,2,1,7,9,3,1,7,10,4,1,_DG⁡LieAlgebra,sp4R,10,table( [( "rank" ) = [2], ( "algebratype" ) = "spnR", ( "vectortable" ) = table( [( "A" ) = table( [( [2, 2] ) = 4, ( [2, 1] ) = 3, ( [1, 1] ) = 1, ( [1, 2] ) = 2 ] ), ( "B" ) = table( [( [2, 4] ) = 7, ( [1, 4] ) = 6, ( [1, 3] ) = 5 ] ), ( "C" ) = table( [( [4, 2] ) = 10, ( [3, 1] ) = 8, ( [3, 2] ) = 9 ] ) ] ), ( "representationdimension" ) = 4, ( "IndTable" ) = [["A", [1, 1], [[[1, 1], 1], [[3, 3], -1]]], ["A", [1, 2], [[[1, 2], 1], [[4, 3], -1]]], ["A", [2, 1], [[[2, 1], 1], [[3, 4], -1]]], ["A", [2, 2], [[[2, 2], 1], [[4, 4], -1]]], ["B", [1, 3], [[[1, 3], 1]]], ["B", [1, 4], [[[1, 4], 1], [[2, 3], 1]]], ["B", [2, 4], [[[2, 4], 1]]], ["C", [3, 1], [[[3, 1], 1]]], ["C", [3, 2], [[[3, 2], 1], [[4, 1], 1]]], ["C", [4, 2], [[[4, 2], 1]]]] ] ),1,2,2,1,1,3,3,−1,1,5,5,2,1,6,6,1,1,8,8,−2,1,9,9,−1,2,3,1,1,2,3,4,−1,2,4,2,1,2,6,5,2,2,7,6,1,2,8,9,−1,2,9,10,−2,3,4,3,−1,3,5,6,1,3,6,7,2,3,9,8,−2,3,10,9,−1,4,6,6,1,4,7,7,2,4,9,9,−1,4,10,10,−2,5,8,1,1,5,9,2,1,6,8,3,1,6,9,1,1,6,9,4,1,6,10,2,1,7,9,3,1,7,10,4,1,_DG⁡LieAlgebra,sp4R,10,table( [( "rank" ) = [2], ( "algebratype" ) = "spnR", ( "vectortable" ) = table( [( "A" ) = table( [( [2, 2] ) = 4, ( [2, 1] ) = 3, ( [1, 1] ) = 1, ( [1, 2] ) = 2 ] ), ( "B" ) = table( [( [2, 4] ) = 7, ( [1, 4] ) = 6, ( [1, 3] ) = 5 ] ), ( "C" ) = table( [( [4, 2] ) = 10, ( [3, 1] ) = 8, ( [3, 2] ) = 9 ] ) ] ), ( "representationdimension" ) = 4, ( "IndTable" ) = [["A", [1, 1], [[[1, 1], 1], [[3, 3], -1]]], ["A", [1, 2], [[[1, 2], 1], [[4, 3], -1]]], ["A", [2, 1], [[[2, 1], 1], [[3, 4], -1]]], ["A", [2, 2], [[[2, 2], 1], [[4, 4], -1]]], ["B", [1, 3], [[[1, 3], 1]]], ["B", [1, 4], [[[1, 4], 1], [[2, 3], 1]]], ["B", [2, 4], [[[2, 4], 1]]], ["C", [3, 1], [[[3, 1], 1]]], ["C", [3, 2], [[[3, 2], 1], [[4, 1], 1]]], ["C", [4, 2], [[[4, 2], 1]]]] ] ),1,2,2,1,1,3,3,−1,1,5,5,2,1,6,6,1,1,8,8,−2,1,9,9,−1,2,3,1,1,2,3,4,−1,2,4,2,1,2,6,5,2,2,7,6,1,2,8,9,−1,2,9,10,−2,3,4,3,−1,3,5,6,1,3,6,7,2,3,9,8,−2,3,10,9,−1,4,6,6,1,4,7,7,2,4,9,9,−1,4,10,10,−2,5,8,1,1,5,9,2,1,6,8,3,1,6,9,1,1,6,9,4,1,6,10,2,1,7,9,3,1,7,10,4,1,_DG⁡LieAlgebra,sp4R,10,table( [( "rank" ) = [2], ( "algebratype" ) = "spnR", ( "vectortable" ) = table( [( "A" ) = table( [( [2, 2] ) = 4, ( [2, 1] ) = 3, ( [1, 1] ) = 1, ( [1, 2] ) = 2 ] ), ( "B" ) = table( [( [2, 4] ) = 7, ( [1, 4] ) = 6, ( [1, 3] ) = 5 ] ), ( "C" ) = table( [( [4, 2] ) = 10, ( [3, 1] ) = 8, ( [3, 2] ) = 9 ] ) ] ), ( "representationdimension" ) = 4, ( "IndTable" ) = [["A", [1, 1], [[[1, 1], 1], [[3, 3], -1]]], ["A", [1, 2], [[[1, 2], 1], [[4, 3], -1]]], ["A", [2, 1], [[[2, 1], 1], [[3, 4], -1]]], ["A", [2, 2], [[[2, 2], 1], [[4, 4], -1]]], ["B", [1, 3], [[[1, 3], 1]]], ["B", [1, 4], [[[1, 4], 1], [[2, 3], 1]]], ["B", [2, 4], [[[2, 4], 1]]], ["C", [3, 1], [[[3, 1], 1]]], ["C", [3, 2], [[[3, 2], 1], [[4, 1], 1]]], ["C", [4, 2], [[[4, 2], 1]]]] ] ),1,2,2,1,1,3,3,−1,1,5,5,2,1,6,6,1,1,8,8,−2,1,9,9,−1,2,3,1,1,2,3,4,−1,2,4,2,1,2,6,5,2,2,7,6,1,2,8,9,−1,2,9,10,−2,3,4,3,−1,3,5,6,1,3,6,7,2,3,9,8,−2,3,10,9,−1,4,6,6,1,4,7,7,2,4,9,9,−1,4,10,10,−2,5,8,1,1,5,9,2,1,6,8,3,1,6,9,1,1,6,9,4,1,6,10,2,1,7,9,3,1,7,10,4,1,_DG⁡LieAlgebra,sp4R,10,table( [( "rank" ) = [2], ( "algebratype" ) = "spnR", ( "vectortable" ) = table( [( "A" ) = table( [( [2, 2] ) = 4, ( [2, 1] ) = 3, ( [1, 1] ) = 1, ( [1, 2] ) = 2 ] ), ( "B" ) = table( [( [2, 4] ) = 7, ( [1, 4] ) = 6, ( [1, 3] ) = 5 ] ), ( "C" ) = table( [( [4, 2] ) = 10, ( [3, 1] ) = 8, ( [3, 2] ) = 9 ] ) ] ), ( "representationdimension" ) = 4, ( "IndTable" ) = [["A", [1, 1], [[[1, 1], 1], [[3, 3], -1]]], ["A", [1, 2], [[[1, 2], 1], [[4, 3], -1]]], ["A", [2, 1], [[[2, 1], 1], [[3, 4], -1]]], ["A", [2, 2], [[[2, 2], 1], [[4, 4], -1]]], ["B", [1, 3], [[[1, 3], 1]]], ["B", [1, 4], [[[1, 4], 1], [[2, 3], 1]]], ["B", [2, 4], [[[2, 4], 1]]], ["C", [3, 1], [[[3, 1], 1]]], ["C", [3, 2], [[[3, 2], 1], [[4, 1], 1]]], ["C", [4, 2], [[[4, 2], 1]]]] ] ),1,2,2,1,1,3,3,−1,1,5,5,2,1,6,6,1,1,8,8,−2,1,9,9,−1,2,3,1,1,2,3,4,−1,2,4,2,1,2,6,5,2,2,7,6,1,2,8,9,−1,2,9,10,−2,3,4,3,−1,3,5,6,1,3,6,7,2,3,9,8,−2,3,10,9,−1,4,6,6,1,4,7,7,2,4,9,9,−1,4,10,10,−2,5,8,1,1,5,9,2,1,6,8,3,1,6,9,1,1,6,9,4,1,6,10,2,1,7,9,3,1,7,10,4,1
DGsetup⁡LD
Lie algebra: sp4R
Here are the 10 matrices for sp4, R.
A ≔ StandardRepresentation⁡sp4R
Let us find the 2-forms which are invariant with respect to these matrices. First define a 4-dimensional space.
DGsetup⁡x1,x2,x3,x4,V:
Generate a basis of 2-forms on V.
Ω ≔ Tools:-GenerateForms⁡dx1,dx2,dx3,dx4,2
_DG⁡form,V,2,1,2,1,_DG⁡form,V,2,1,3,1,_DG⁡form,V,2,1,4,1,_DG⁡form,V,2,2,3,1,_DG⁡form,V,2,2,4,1,_DG⁡form,V,2,3,4,1,_DG⁡form,V,2,1,2,1,_DG⁡form,V,2,1,3,1,_DG⁡form,V,2,1,4,1,_DG⁡form,V,2,2,3,1,_DG⁡form,V,2,2,4,1,_DG⁡form,V,2,3,4,1,_DG⁡form,V,2,1,2,1,_DG⁡form,V,2,1,3,1,_DG⁡form,V,2,1,4,1,_DG⁡form,V,2,2,3,1,_DG⁡form,V,2,2,4,1,_DG⁡form,V,2,3,4,1,_DG⁡form,V,2,1,2,1,_DG⁡form,V,2,1,3,1,_DG⁡form,V,2,1,4,1,_DG⁡form,V,2,2,3,1,_DG⁡form,V,2,2,4,1,_DG⁡form,V,2,3,4,1,_DG⁡form,V,2,1,2,1,_DG⁡form,V,2,1,3,1,_DG⁡form,V,2,1,4,1,_DG⁡form,V,2,2,3,1,_DG⁡form,V,2,2,4,1,_DG⁡form,V,2,3,4,1,_DG⁡form,V,2,1,2,1,_DG⁡form,V,2,1,3,1,_DG⁡form,V,2,1,4,1,_DG⁡form,V,2,2,3,1,_DG⁡form,V,2,2,4,1,_DG⁡form,V,2,3,4,1,_DG⁡form,V,2,1,2,1,_DG⁡form,V,2,1,3,1,_DG⁡form,V,2,1,4,1,_DG⁡form,V,2,2,3,1,_DG⁡form,V,2,2,4,1,_DG⁡form,V,2,3,4,1,_DG⁡form,V,2,1,2,1,_DG⁡form,V,2,1,3,1,_DG⁡form,V,2,1,4,1,_DG⁡form,V,2,2,3,1,_DG⁡form,V,2,2,4,1,_DG⁡form,V,2,3,4,1
The InvariantTensorsAtAPoint command shows that all 2-forms which are invariant with respect to the matrices A are multiples of a single non-degenerate 2-form.
InvariantTensorsAtAPoint⁡A,Ω
_DG⁡form,V,2,1,3,1,2,4,1,_DG⁡form,V,2,1,3,1,2,4,1,_DG⁡form,V,2,1,3,1,2,4,1,_DG⁡form,V,2,1,3,1,2,4,1,_DG⁡form,V,2,1,3,1,2,4,1,_DG⁡form,V,2,1,3,1,2,4,1,_DG⁡form,V,2,1,3,1,2,4,1,_DG⁡form,V,2,1,3,1,2,4,1
Example 4.
The calculations of invariant tensors can be done in an anholonomic frame. (See FrameData.)
FD ≔ FrameData⁡dx+y⁢dz,dy,dz,N
_DG⁡moving_frame,N,3,M,x,y,z,form,1,1,1,3,1,−y,2,2,1,3,3,1,2,3,1,−1,_DG⁡moving_frame,N,3,M,x,y,z,form,1,1,1,3,1,−y,2,2,1,3,3,1,2,3,1,−1,_DG⁡moving_frame,N,3,M,x,y,z,form,1,1,1,3,1,−y,2,2,1,3,3,1,2,3,1,−1,_DG⁡moving_frame,N,3,M,x,y,z,form,1,1,1,3,1,−y,2,2,1,3,3,1,2,3,1,−1,_DG⁡moving_frame,N,3,M,x,y,z,form,1,1,1,3,1,−y,2,2,1,3,3,1,2,3,1,−1,_DG⁡moving_frame,N,3,M,x,y,z,form,1,1,1,3,1,−y,2,2,1,3,3,1,2,3,1,−1,_DG⁡moving_frame,N,3,M,x,y,z,form,1,1,1,3,1,−y,2,2,1,3,3,1,2,3,1,−1,_DG⁡moving_frame,N,3,M,x,y,z,form,1,1,1,3,1,−y,2,2,1,3,3,1,2,3,1,−1
DGsetup⁡FD,'X1','X2','X3','ω1','ω2','ω3'
frame name: N
A ≔ Matrix⁡0,1,0,0,0,1,0,0,0
Here is a basis for the A-invariant vectors.
B ≔ X1,X2,X3
_DG⁡vector,N,,1,1,_DG⁡vector,N,,2,1,_DG⁡vector,N,,3,1
InvariantTensorsAtAPoint⁡A,B
_DG⁡vector,N,,1,1
Here is a basis for the A-invariant 1-forms.
Ω1 ≔ ω1,ω2,ω3
_DG⁡form,N,1,1,1,_DG⁡form,N,1,2,1,_DG⁡form,N,1,3,1
InvariantTensorsAtAPoint⁡A,Ω1
_DG⁡form,N,1,3,1
Here is a basis for the A-invariant 2-forms.
Ω2 ≔ evalDG⁡ω1 &w ω2,ω1 &w ω3,ω2 &w ω3
_DG⁡form,N,2,1,2,1,_DG⁡form,N,2,1,3,1,_DG⁡form,N,2,2,3,1,_DG⁡form,N,2,1,2,1,_DG⁡form,N,2,1,3,1,_DG⁡form,N,2,2,3,1,_DG⁡form,N,2,1,2,1,_DG⁡form,N,2,1,3,1,_DG⁡form,N,2,2,3,1,_DG⁡form,N,2,1,2,1,_DG⁡form,N,2,1,3,1,_DG⁡form,N,2,2,3,1,_DG⁡form,N,2,1,2,1,_DG⁡form,N,2,1,3,1,_DG⁡form,N,2,2,3,1,_DG⁡form,N,2,1,2,1,_DG⁡form,N,2,1,3,1,_DG⁡form,N,2,2,3,1,_DG⁡form,N,2,1,2,1,_DG⁡form,N,2,1,3,1,_DG⁡form,N,2,2,3,1,_DG⁡form,N,2,1,2,1,_DG⁡form,N,2,1,3,1,_DG⁡form,N,2,2,3,1
InvariantTensorsAtAPoint⁡A,Ω2
_DG⁡form,N,2,2,3,1,_DG⁡form,N,2,