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Example 1.
We define a 5-dimensional representation of a 3-dimensional solvable Lie algebra.
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| (2.1) |
alg1 >
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V1 >
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V1 >
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We find a new basis for the representation space in which the matrices are all upper triangular.
alg1 >
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To verify this result we use the ChangeRepresentationBasis command to change basis in the representation space.
V1 >
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Example 2.
We define a 6-dimensional representation of a 3-dimensional solvable Lie algebra.
alg1 >
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| (2.2) |
Alg2 >
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V2 >
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V2 >
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In this example some of the eigenvectors found by the RepresentationEigenvector program are complex and it is not possible to find a real basis in which the representation is upper triangular.
Alg2 >
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Alg2 >
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V2 >
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To obtain an upper triangular representation with respect to a complex basis, use the optional argument fieldextension = I.
Alg2 >
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V2 >
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Example 3.
If the name of an algebra is passed to the program SolvableRepresentation, then the assumed representation is the adjoint representation of the algebra (or current frame).
Alg2 >
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The adjoint representation of this algebra is not upper triangular.
Alg3 >
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| (2.6) |
Alg3 >
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Now in this new basis the adjoint representation is upper triangular.
Example 4.
An example with complex eigenvalues.
Alg4 >
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| (2.8) |
Alg5 >
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| (2.9) |
Alg5 >
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In this new basis the adjoint representation is upper triangular except for a 2x2 "complex" block on the diagonal for ad(e4).
We rerun this example with the option fieldextension = I
Alg5 >
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| (2.11) |
Alg5 >
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Example 5.
Let be a representation of a nilpotent Lie algebra on a vector space . The representation is called a nilrepresentation if each matrix is nilpotent, that is for some Engel's theorem (see, for example, Fulton and Harris, page 125 or Varadarajan, page 189) asserts that if rho is a nilrepresentation, then there is a basis for V for which all the representation matrices are strictly upper triangular.
Alg5 >
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| (2.13) |
Alg5 >
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V5 >
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V5 >
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Check that Alg5 is a nilpotent algebra, that rho is a representation, and that rho is a nilrepresentation.
Alg5 >
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Alg5 >
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Alg5 >
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Alg5 >
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| (2.17) |
Alg5 >
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In this new basis the ad matrices are all nilpotent.