fix: wrong addeq! for MatAlgebraElem (#1548)

- fixes #1547
thofma · Jun 19, 2024 · 3c29ce9 · 3c29ce9
1 parent 5d876ad
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diff --git a/src/AlgAss/AlgMatElem.jl b/src/AlgAss/AlgMatElem.jl
@@ -149,6 +149,16 @@ function mul!(c::T, a::T, b::T) where {T <: MatAlgebraElem}
   return c
 end
 
+function addeq!(b::T, a::T) where {T <: MatAlgebraElem}
+  parent(a) != parent(b) && error("Parents don't match.")
+  A = parent(a)
+
+  b.matrix = addeq!(b.matrix, a.matrix)
+  b.has_coeffs = false
+
+  return b
+end
+
 ################################################################################
 #
 #  Ad hoc operations

diff --git a/test/AlgAss/Elem.jl b/test/AlgAss/Elem.jl
@@ -58,4 +58,13 @@
   # mul! for matrix algebra elements
   A = matrix_algebra(QQ, 2)
   @test isone(mul!(zero(A), one(A), ZZRingElem(1)))
+
+  # add! for matrix algebra elements
+  # 1547
+  let
+    A = matrix_algebra(QQ, 2)
+    b = A(matrix(QQ, [3 4; 5 6]))
+    Hecke.addeq!(b,b)
+    @test b == A(matrix(QQ, [6 8; 10 12]))
+  end
 end