From 5c2fabfb0827fabfcaa135c6c4a069e14997b475 Mon Sep 17 00:00:00 2001
From: kalmar <kalmar@amu.edu.pl>
Date: Wed, 19 Jul 2017 22:38:17 +0200
Subject: [PATCH] make another version of mul! for GroupRingElts

---
 src/GroupRings.jl | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/src/GroupRings.jl b/src/GroupRings.jl
index ad7d948..9bfd581 100644
--- a/src/GroupRings.jl
+++ b/src/GroupRings.jl
@@ -335,12 +335,23 @@ function mul!{T}(result::AbstractVector{T},
    end
 end
 
-function mul!{T}(result::GroupRingElem{T}, X::GroupRingElem{T}, Y::GroupRingElem{T})
-   # @show result === X
+function mul!{T}(result::GroupRingElem{T}, X::GroupRingElem, Y::GroupRingElem)
    if result === X
       result = deepcopy(result)
    end
-   mul!(result.coeffs, X.coeffs, Y.coeffs, parent(X).pm)
+
+   z = zero(T)
+   result.coeffs .= z
+
+   for j in eachindex(Y.coeffs)
+      if Y.coeffs[j] != z
+         for i in eachindex(X.coeffs)
+            if X.coeffs[i] != z
+               result.coeffs[parent(X).pm[i,j]] += X[i]*Y[j]
+            end
+         end
+      end
+   end
    return result
 end