From 4b6c2e681f71d2220277555a0a2fd59222c9e002 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lars=20G=C3=B6ttgens?= <lars.goettgens@rwth-aachen.de>
Date: Tue, 19 Nov 2024 12:07:41 +0100
Subject: [PATCH] fix: unary minus for sparse group algebra elems

---
 src/AlgAss/Elem.jl    | 8 ++++++--
 test/AlgAss/AlgGrp.jl | 2 ++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/AlgAss/Elem.jl b/src/AlgAss/Elem.jl
index 46e8d75b69..6f7970a8a5 100644
--- a/src/AlgAss/Elem.jl
+++ b/src/AlgAss/Elem.jl
@@ -147,8 +147,12 @@ end
 ################################################################################
 
 function -(a::AbstractAssociativeAlgebraElem{T}) where {T}
-  v = T[ -coefficients(a, copy = false)[i] for i = 1:dim(parent(a)) ]
-  return parent(a)(v)
+  if _is_sparse(a)
+    return parent(a)(-a.coeffs_sparse)
+  else
+    v = T[ -coefficients(a, copy = false)[i] for i = 1:dim(parent(a)) ]
+    return parent(a)(v)
+  end
 end
 
 ################################################################################
diff --git a/test/AlgAss/AlgGrp.jl b/test/AlgAss/AlgGrp.jl
index 3413ff06e0..7ee39d22ca 100644
--- a/test/AlgAss/AlgGrp.jl
+++ b/test/AlgAss/AlgGrp.jl
@@ -107,6 +107,7 @@
       @test aa * bb == cc
       @test bb * aa == dd
       @test (aa + bb)^2 == QG(a)^2 + cc + dd + QG(b)^2
+      @test aa - bb == aa + (-bb)
     end
   end
 
@@ -129,6 +130,7 @@
       @test aa * bb == cc
       @test bb * aa == dd
       @test (aa + bb)^2 == QG(a)^2 + cc + dd + QG(b)^2
+      @test aa - bb == aa + (-bb)
     end
   end