From e223763b75db2e8a24a19b198537d4ef0797bab5 Mon Sep 17 00:00:00 2001
From: kalmarek <kalmar@amu.edu.pl>
Date: Sun, 10 Sep 2017 21:41:36 +0200
Subject: [PATCH] add check_pm function to test against zeros;

Since we can not throw from a thread, after introduction of Threading
into create_pm doesn't warn user on the possible not supported product.
Indeed threading quits immediately after first error is thrown, leaving
the pm matrix under-populated;
we check on zeros and warn the user on the situation;
---
 src/GroupRings.jl | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/src/GroupRings.jl b/src/GroupRings.jl
index 5524863..2349831 100644
--- a/src/GroupRings.jl
+++ b/src/GroupRings.jl
@@ -518,7 +518,7 @@ function reverse_dict(iter)
 end
 
 function create_pm{T<:GroupElem}(basis::Vector{T}, basis_dict::Dict{T, Int},
-   limit::Int=length(basis); twisted::Bool=false)
+   limit::Int=length(basis); twisted::Bool=false, check=true)
    product_matrix = zeros(Int, (limit,limit))
    Threads.@threads for i in 1:limit
       x = basis[i]
@@ -526,12 +526,29 @@ function create_pm{T<:GroupElem}(basis::Vector{T}, basis_dict::Dict{T, Int},
          x = inv(x)
       end
       for j in 1:limit
-         product_matrix[i,j] = basis_dict[x*(basis[j])]
+         product_matrix[i,j] = basis_dict[x*basis[j]]
       end
    end
+
+   check && check_pm(product_matrix, basis, twisted)
+
    return product_matrix
 end
 
+function check_pm(product_matrix, basis, twisted)
+   idx = findfirst(product_matrix' .== 0)
+   if idx != 0
+      warn("Product is not supported on basis")
+      i,j = ind2sub(product_matrix, idx)
+      x = basis[i]
+      if twisted
+         x = inv(x)
+      end
+      throw(KeyError(x*basis[j]))
+   end
+   return true
+end
+
 create_pm{T<:GroupElem}(b::Vector{T}) = create_pm(b, reverse_dict(b))
 
 function complete!(RG::GroupRing)