Creation of Group Representations

Contents

General Group Representations

GroupRepresentation(G, M, action) : Grp, CombFreeMod, MonStgElt -> ModRed
GroupRepresentation(G, M, action) : GrpRed, CombFreeMod, MonStgElt -> ModRed
    params: List                        Default: [* *]
Constructs a group representation for the group G on the combinatorial free module M with basis B, such that the action on basis elements G x B to M is described by the map given by the string action.

Subrepresentations

Subrepresentation(V, t) : ModRed, Any -> ModRed, ModRedHom
SubCFModule(V, t) : CombFreeMod, Any -> CombFreeMod, CombFreeModHom
The subrepresentation (or submodule) of V whose underlying free module is generated by t.

Natural Representations

TrivialRepresentation(G, R) : Grp, Rng -> ModRed
TrivialRepresentation(G, R) : GrpRed, Rng -> ModRed
    name: MonStgElt                     Default: "v"
The trivial representation for the group G over the ring R, where the basis element has name name.
StandardRepresentation(G) : GrpMat -> ModRed
StandardRepresentation(G) : GrpRed -> ModRed
    name: MonStgElt                     Default: "x"
The standard representation of the matrix group G over its ring of definition R, i.e. the representation obtained by considering its given embedding in GLn(R) acting on Rn by invertible linear transformations. The basis will have names x1, ..., xn, where x is specified by name.
SpinorNormRepresentation(G, d) : GrpRed, RngIntElt -> ModRed
    name: MonStgElt                     Default: "x"
The 1-dimensional representation spind of the orthogonal group G induced by the spinor norm and d.
Rho(G, k, j) : GrpMat, RngIntElt, RngIntElt -> ModRed
The representation detk tensor Symj.
SymSpinor(G, d, k) : GrpRed, RngIntElt, RngIntElt -> ModRed
The representation spind tensor Symk of the orthogonal group G.
AltSpinor(G, d) : GrpRed, RngIntElt, RngIntElt -> ModRed
The representation spind tensor Altj of the orthogonal group G.
RadicalSignCharacterSinglePrime(G, p) : GrpRed, RngIntElt -> ModRed
The character θp from [DPRT24]. If G = OO(Q) is an orthogonal group defined over Q, with Q integral, and p is a prime divisor of Disc(Q), returns the 1-dimensional representation of G(Zp) on the determinant of the radical of Q mod 2p.
RadicalSignCharacter(G, d) : GrpRed, RngIntElt -> ModRed
The character θd = ∏p | d θp, where θp is the character constructed by the function RadicalSignCharacterSinglePrime.
SpinRepresentation(G, p) : GrpRed, RngIntElt -> ModRed
The spin representation of the special orthogonal group G=SO(Q) with coefficients in Fp.

New Representations from Old

DeterminantRepresentation(G) : GrpMat -> ModRed
    k: RngIntElt                        Default: 1
    name: MonStgElt                     Default: "v"
The 1-dimensional representation, where G acts via the g |-> det(g)k, where the basis element has name name.
SymmetricRepresentation(V, n) : ModRed, RngIntElt -> ModRed
The symmetric representation Symn(V).
AlternatingRepresentation(V, n) : ModRed, RngIntElt -> ModRed
The alternating representation Altn(V).
DualRepresentation(V) : ModRed -> ModRed
The dual (contragredient) representation Vv.
TensorProduct(V, W) : ModRed, ModRed -> ModRed
The representation V tensor W with the diagonal action.
TensorPower(V, d) : ModRed, RngIntElt -> ModRed
The tensor power representation V tensor d, with the diagonal action.
Pullback(V, f, G) : ModRed, MonStgElt, Grp -> ModRed
If f : G to H is a group homomorphism, and V is a representation of H, returns the pullback of V via f to a representation of G. Does not verify that f is a group homomorphism.

New Combinatorially Free Modules from Old

ExteriorPower(M, n) : CombFreeMod, RngIntElt -> CombFreeMod
AlternatingPower(M, n) : CombFreeMod, RngIntElt -> CombFreeMod
Returns bigwedgen M.
ExteriorAlgebra(M) : CombFreeMod -> CombFreeMod, CombFreeModHom
The underlying module of the exterior algebra of M, namely bigwedge M, together with an embedding of M as the degree 1 component.
DirectSum(M) : [ CombFreeMod ] -> CombFreeMod
The direct sum bigoplusi Mi.

Highest Weight Representations

GroupRepresentation(G, w) : GrpLie, [ RngIntElt ] -> ModRed
The algebraic representation of the group G with highest weight w. Embeds the group of Lie type G into its standard representation.
HighestWeightRepresentation(G, w) : GrpRed, [ RngIntElt ] -> ModRed
The irreducible algebraic representation of G with highest weight w.
HighestWeightRepresentation(G, w, p) : GrpRed, [ RngIntElt ], RngIntElt -> ModRed
If G is a reductive group defined over a number field F, return the irreducible algebraic representation of G with highest weight w, and coefficient field of characteristic p, obtained by the reduction modulo a prime P of F above p.

Creation of Combinatorial Free Modules

CombinatorialFreeModule(R, S) : Rng, SetIndx -> CombFreeMod
CombinatorialFreeModule(R, S) : Rng, [ MonStgElt ] -> CombFreeMod
    params: List                        Default: [* *]
A combinatorial free module over the ring R with basis given by S, namely M = RS.
V2.29, 21 October 2025