From 464faa083e5744cd9a92d89079226adad3ec16a4 Mon Sep 17 00:00:00 2001
From: Oscar Dowson <odow@users.noreply.github.com>
Date: Tue, 3 Nov 2020 02:26:25 +1300
Subject: [PATCH] Fix bug in matrix add_mul (#55)

---
 src/linear_algebra.jl | 2 +-
 test/matmul.jl        | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/linear_algebra.jl b/src/linear_algebra.jl
index f3a54e6..99ec584 100644
--- a/src/linear_algebra.jl
+++ b/src/linear_algebra.jl
@@ -180,7 +180,7 @@ function _add_mul_array(C::Matrix, A::AbstractMatrix, B::AbstractMatrix)
 
     @inbounds begin
         for i = 1:size(A, 1), j = 1:size(B, 2)
-            Ctmp = zero!(C[i, j])
+            Ctmp = C[i, j]
             for k = 1:size(A, 2)
                 Ctmp = buffered_operate!(mul_buffer, add_mul, Ctmp, A[i, k], B[k, j])
             end
diff --git a/test/matmul.jl b/test/matmul.jl
index 0b16ea6..bf69c73 100644
--- a/test/matmul.jl
+++ b/test/matmul.jl
@@ -147,3 +147,11 @@ end
         alloc_test(() -> MA.mutable_operate!(MA.add_mul, C, A, B), 48)
     end
 end
+
+@testset "matrix multiplication" begin
+    X = ones(BigInt, 1, 1)
+    M = ones(1, 1);
+    C = X * M
+    D = MA.operate!(MA.add_mul, C, X, M)
+    @test D == X * M + X * M
+end