constructors for GroupRing

src/GroupAlgebras.jl

@@ -37,6 +37,28 @@ GroupRingElem{T}(c::AbstractVector{T}, A::GroupRing) = GroupRingElem{T}(c,A)
 
 convert{T<:Number}(::Type{T}, X::GroupRingElem) =
    GroupRingElem(parent(X), convert(AbstractVector{T}, X.coeffs))
+
+function GroupRing(G::Group, pm::Array{Int,2})
+   size(pm,1) == size(pm,2) || throw("pm must be of size (n,n), got
+      $(size(pm))")
+   return GroupRing(Group, pm)
+end
+
+function GroupRing(G::Group, pm::Array{Int,2}, basis::Vector)
+   size(pm,1) == size(pm,2) || throw("pm must be of size (n,n), got
+      $(size(pm))")
+   eltype(basis) == elem_type(G) || throw("basis must consist of elements of $G")
+   basis_dict = Dict(g => i for (i,g) in enumerate(basis))
+   return GroupRing(Group, pm, basis, basis_dict)
+end
+
+function GroupRing(G::Group; complete=false)
+   A = GroupRing(Group)
+   if complete
+      complete(A)
+   end
+   return A
+end
 end
 
 (==)(X::GroupAlgebraElement, Y::GroupAlgebraElement) = isequal(X,Y)