LieAlgbebras[SimpleLieAlgebraData] - obtain the structure equations for a classical matrix Lie algebra
Calling Sequences
SimpleLieAlgebraData(
Parameters
algtype - a string, describing the type and dimension of a classical matrix algebra
algname - an unassigned name or a string, the name of the classical matrix algebra to be constructed
options - (optional) keyword arguments labelformat, labels which specify the labelling of the basis for the Lie algebra. Different standard basis for some of the Lie algebras can be specified with the keyword version.
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Description
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This command returns the structure equations (see LieAlgebraData) for any one of the following Lie algebras:
Type
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Lie algebra
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A
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(two versions),
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B
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(two versions)
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C
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,
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D
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(two versions)
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Other
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,
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The Lie algebras are all simple Lie algebras. The are classical matrix algebras which are often used in Lie theory and differential geometry.
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Subalgebras of any of these Lie algebras can be calculate using the command MatrixSubalgebras.
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Two versions of the Lie algebras and are available, corresponding the choices
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for the quadratic form preserved by these algebras. The keyword argument version specifies the choice. The default is version = 1. This choice is preferred for roots space computations.
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The keyword arguments labelformat, labels allow for the labeling of the basis of the abstract Lie algebra which characteristizes the basis elements in terms of their standard matrix elements. See LieAlgebraData, DGsetup.
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Examples
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>
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with(DifferentialGeometry): with(LieAlgebras):
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Example 1.
Initialize the Lie algebra the Lie algebra of trace-free 3×3 matrices.
>
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LD1 := SimpleLieAlgebraData("sl(3)", alg1, labelformat = "gl", labels = ['E', 'theta']);
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| (2.1) |
When this output is passed to DGsetup, the 8-dimensional Lie algebra with the foregoing structure equations is initialized and the unassigned names are assigned as vectors and 1-forms for this Lie algebra.
| (2.2) |
Here is the Lie bracket multiplication table for .
alg1 >
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MultiplicationTable("LieTable");
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| (2.3) |
This coincides with the commutator formulas for the standard matrix representation of .
alg1 >
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StandardRepresentation(alg1);
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| (2.4) |
The 3rd basis element matches the 3rd matrix in the standard representation and is precisely the elementary matrix with a 1 in the 1st column, 2nd row.
Example 2
We initialize the Lie algebra in two different basis. Our first version is:
alg1 >
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LD2a := SimpleLieAlgebraData("so(3, 1)", so31a, labelformat = "gl", labels = ['X', 'zeta']);
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| (2.5) |
| (2.6) |
so31a >
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MultiplicationTable("LieTable");
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| (2.7) |
Our second version is :
so31a >
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LD2b := SimpleLieAlgebraData("so(3, 1)", so31b, labelformat = "gl", labels = ['Y', 'xi'], version = 2);
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| (2.8) |
| (2.9) |
so31a >
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MultiplicationTable("LieTable");
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| (2.10) |
From the standard matrix representations for these 2 Lie algebras we can construct a Lie algebra isomophism . First let us define the quadratic forms used in each version.
so31b >
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with(LinearAlgebra):
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so31b >
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Qa := Matrix([[0, 1, 0, 0], [1, 0, 0, 0], [0, 0, 1, 0], [0, 0, 0, 1]]);
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| (2.11) |
so31b >
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Qb := Matrix([[1, 0, 0, 0], [0, 1, 0, 0], [0, 0, 1, 0], [0, 0, 0, -1]]);
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| (2.12) |
Here is the change of basis matrix relating to .
so31b >
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P := Matrix([[0,0,1/sqrt(2), 1/sqrt(2)],[0,0,1/sqrt(2), -1/sqrt(2)], [0, 1, 0, 0], [1, 0, 0, 0]]);
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| (2.13) |
so31b >
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Transpose(P).Qa.P;
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| (2.14) |
Here is the standard representation for using .
so31b >
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A := StandardRepresentation(so31a);
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| (2.15) |
Here is the standard representation for using
so31b >
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B := StandardRepresentation(so31b);
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| (2.16) |
Here are the matrices under the change of basis defined by Since the resulting matrics now preserve , they must be linear combinations of the matrices B.
so31b >
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A1 := [seq(P^(-1).a.P, a = A)];
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| (2.17) |
so31b >
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C := GetComponents(A1, B);
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| (2.18) |
These components specify the matrix of the isomorphism we want.
so31b >
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Phi := Transformation(so31a, so31b, Transpose(Matrix(C)));
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| (2.19) |
so31b >
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Query(Phi, "Homomorphism");
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| (2.20) |
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