From 8d1604863cfc33c9538a18b85496db4d605493ec Mon Sep 17 00:00:00 2001
From: kalmar <kalmar@amu.edu.pl>
Date: Thu, 27 Jul 2017 22:09:48 +0200
Subject: [PATCH] RG(::Vector{GroupElem}) method for constructing
 GroupRingElems

---
 src/GroupRings.jl | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/GroupRings.jl b/src/GroupRings.jl
index d2cf331..7a4ad4e 100644
--- a/src/GroupRings.jl
+++ b/src/GroupRings.jl
@@ -136,7 +136,7 @@ function (RG::GroupRing)(g::GroupElem, T::Type=Int)
    return result
 end
 
-function (RG::GroupRing)(x::AbstractVector)
+function (RG::GroupRing){T<:Number}(x::AbstractVector{T})
    isdefined(RG, :basis) || throw("Can not coerce without basis of GroupRing")
    length(x) == length(RG.basis) || throw("Can not coerce to $RG: lengths differ")
    result = RG(eltype(x))
@@ -144,6 +144,16 @@ function (RG::GroupRing)(x::AbstractVector)
    return result
 end
 
+function (RG::GroupRing{Gr,T}){Gr<:Nemo.Group, T<:Nemo.GroupElem}(V::Vector{T},
+   S::Type=Rational{Int}; alt=false)
+    res = RG(S)
+    for g in V
+        c = (alt ? sign(g)*one(S) : one(S))
+        res[g] += c/length(V)
+    end
+    return res
+end
+
 function (RG::GroupRing)(X::GroupRingElem)
    RG == parent(X) || throw("Can not coerce!")
    return RG(X.coeffs)