Add generic implementation of axpby and axpy (#394)

Author: bjarthur

src/host/linalg.jl

@@ -293,3 +293,11 @@ function Base.similar(A::Hermitian{<:Any,<:AbstractGPUArray}, ::Type{T}) where T
     fill!(view(B, diagind(B)), 0)
     return Hermitian(B, ifelse(A.uplo == 'U', :U, :L))
 end
+
+
+## axp{b}y
+
+LinearAlgebra.axpby!(alpha::Number, x::AbstractGPUArray,
+                     beta::Number,  y::AbstractGPUArray) = y .= x.*alpha .+ y.*beta
+
+LinearAlgebra.axpy!(alpha::Number, x::AbstractGPUArray, y::AbstractGPUArray) = y .+= x.*alpha

test/testsuite/linalg.jl

@@ -186,6 +186,14 @@
         @test compare(rmul!, AT, rand(T, a), Ref(rand(T)))
         @test compare(lmul!, AT, Ref(rand(T)), rand(T, b))
     end
+
+    @testset "axp{b}y" for T in eltypes
+        alpha, beta = 0.5, 2.0
+        x = T.([2,4,6])
+        y = T.([3,4,5])
+        @test axpby!(alpha,x,beta,y) ≈ T.([7,10,13])
+        @test axpy!(alpha,x,y) ≈ T.([8,12,16])
+    end
 end
 
 @testsuite "linalg/mul!/vector-matrix" (AT, eltypes)->begin