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Construction of Reflection Groups

A reflection group is a group generated by a finite set of pseudoreflections. The simple roots (resp. simple coroots, simple orders) of a reflection group are the roots (resp. coroots, orders) of its generators. The roots (resp. coroots, orders) of a reflection group are the roots (resp. coroots, orders) of all the reflections contained in the group.

See also Section Construction of Real Reflection Groups on the construction of real reflection groups and Section Construction of Finite Complex Reflection Groups on the construction of finite complex reflection groups.

IsReflectionGroup(G) : GrpMat -> BoolElt, [RngIntElt], Mtrx, Mtrx
Returns true if, and only if, the matrix group G is a reflection group with the given generators. If G is a reflection group, the orders, roots and coroots are also returned.
ReflectionGroup(A, B, m) : Mtrx, Mtrx, [RngIntElt] -> GrpMat
The reflection group with simple roots given by the rows of the matrix A, simple coroots given by the rows of the matrix B, and simple orders given by the sequence m=[m1, ..., mn]. If < A[i], B[i] >ne2, then B[i] is multiplied by the appropriate constant.
ReflectionGroup(A, B, m) : [ModTupRngElt], [ModTupRngElt], [RngIntElt] -> GrpMat
The reflection group with simple roots given by the sequence A, simple coroots given by the sequence B, and simple orders given by the sequence m=[m1, ..., mn]. If < A[i], B[i] >ne2, then B[i] is multiplied by the appropriate constant.
ReflectionGroup(A, B) : Mtrx, Mtrx -> GrpMat
The reflection group with simple roots given by the rows of the matrix A and simple coroots given by the rows of the matrix B. The orders are all taken to be 2. If < A[i], B[i] >ne2, then B[i] is multiplied by the appropriate constant.
ReflectionGroup(A, B) : [ModTupRngElt], [ModTupRngElt] -> GrpMat
The reflection group with simple roots given by the sequence A and simple coroots given by the sequence B. The orders are all taken to be 2. If < A[i], B[i] >ne2, then B[i] is multiplied by the appropriate constant.

Example GrpRfl_ReflectionGroups (H80E3)

> F<z> := CyclotomicField(7);
> M := MatrixAlgebra(F, 2);
> A := M!1;
> B := M![1,1,-1,1];
> G := ReflectionGroup(A, B, [2,7]);
> IsReflectionGroup(G);
true [ 2, 7 ]


[1 0]
[0 1]


[ 2  2]
[-2  2]

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