Fix typos in 2x2 matmatmul (#50362)

Author: dkarrasch

stdlib/LinearAlgebra/src/matmul.jl

@@ -1008,18 +1008,18 @@ function matmul2x2!(C::AbstractMatrix, tA, tB, A::AbstractMatrix, B::AbstractMat
         # TODO making these lazy could improve perf
         B11 = copy(B[1,1]'); B12 = copy(B[2,1]')
         B21 = copy(B[1,2]'); B22 = copy(B[2,2]')
-    elseif tA == 'S'
-        B11 = symmetric(A[1,1], :U); B12 = A[1,2]
-        B21 = copy(transpose(A[1,2])); B22 = symmetric(A[2,2], :U)
-    elseif tA == 's'
-        B11 = symmetric(A[1,1], :L); B12 = copy(transpose(A[2,1]))
-        B21 = A[2,1]; B22 = symmetric(A[2,2], :L)
-    elseif tA == 'H'
-        B11 = hermitian(A[1,1], :U); B12 = A[1,2]
-        B21 = copy(adjoint(A[1,2])); B22 = hermitian(A[2,2], :U)
-    else # if tA == 'h'
-        B11 = hermitian(A[1,1], :L); B12 = copy(adjoint(A[2,1]))
-        B21 = A[2,1]; B22 = hermitian(A[2,2], :L)
+    elseif tB == 'S'
+        B11 = symmetric(B[1,1], :U); B12 = B[1,2]
+        B21 = copy(transpose(B[1,2])); B22 = symmetric(B[2,2], :U)
+    elseif tB == 's'
+        B11 = symmetric(B[1,1], :L); B12 = copy(transpose(B[2,1]))
+        B21 = B[2,1]; B22 = symmetric(B[2,2], :L)
+    elseif tB == 'H'
+        B11 = hermitian(B[1,1], :U); B12 = B[1,2]
+        B21 = copy(adjoint(B[1,2])); B22 = hermitian(B[2,2], :U)
+    else # if tB == 'h'
+        B11 = hermitian(B[1,1], :L); B12 = copy(adjoint(B[2,1]))
+        B21 = B[2,1]; B22 = hermitian(B[2,2], :L)
     end
     _modify!(_add, A11*B11 + A12*B21, C, (1,1))
     _modify!(_add, A11*B12 + A12*B22, C, (1,2))

stdlib/LinearAlgebra/test/matmul.jl

@@ -4,10 +4,19 @@ module TestMatmul
 
 using Base: rtoldefault
 using Test, LinearAlgebra, Random
-using LinearAlgebra: mul!
+using LinearAlgebra: mul!, Symmetric, Hermitian
 
 ## Test Julia fallbacks to BLAS routines
 
+mul_wrappers = [
+    m -> m,
+    m -> Symmetric(m, :U),
+    m -> Symmetric(m, :L),
+    m -> Hermitian(m, :U),
+    m -> Hermitian(m, :L),
+    m -> adjoint(m),
+    m -> transpose(m)]
+
 @testset "matrices with zero dimensions" begin
     for (dimsA, dimsB, dimsC) in (
         ((0, 5), (5, 3), (0, 3)),
@@ -42,6 +51,9 @@ end
         @test *(adjoint(Ai), adjoint(Bi)) == [-28.25-66im 9.75-58im; -26-89im 21-73im]
         @test_throws DimensionMismatch [1 2; 0 0; 0 0] * [1 2]
     end
+    for wrapper_a in mul_wrappers, wrapper_b in mul_wrappers
+        @test wrapper_a(AA) * wrapper_b(BB) == Array(wrapper_a(AA)) * Array(wrapper_b(BB))
+    end
     @test_throws DimensionMismatch mul!(Matrix{Float64}(undef, 3, 3), AA, BB)
 end
 @testset "3x3 matmul" begin
@@ -62,6 +74,9 @@ end
         @test *(adjoint(Ai), adjoint(Bi)) == [1+2im 20.75+9im -44.75+42im; 19.5+17.5im -54-36.5im 51-14.5im; 13+7.5im 11.25+31.5im -43.25-14.5im]
         @test_throws DimensionMismatch [1 2 3; 0 0 0; 0 0 0] * [1 2 3]
     end
+    for wrapper_a in mul_wrappers, wrapper_b in mul_wrappers
+        @test wrapper_a(AA) * wrapper_b(BB) == Array(wrapper_a(AA)) * Array(wrapper_b(BB))
+    end
     @test_throws DimensionMismatch mul!(Matrix{Float64}(undef, 4, 4), AA, BB)
 end