Add default definition for evaluating kernel with two arguments

Author: devmotion

src/generic.jl

@@ -5,11 +5,14 @@ Base.length(::Kernel) = 1
 Base.iterate(k::Kernel) = (k,nothing)
 Base.iterate(k::Kernel, ::Any) = nothing
 
+# default fallback for evaluating a kernel with two arguments (such as vectors etc)
+kappa(κ::Kernel, x, y) = kappa(κ, evaluate(metric(κ), transform(κ, x), transform(κ, y)))
+
 ### Syntactic sugar for creating matrices and using kernel functions
 for k in [:ExponentialKernel,:SqExponentialKernel,:GammaExponentialKernel,:MaternKernel,:Matern32Kernel,:Matern52Kernel,:LinearKernel,:PolynomialKernel,:ExponentiatedKernel,:ZeroKernel,:WhiteKernel,:ConstantKernel,:RationalQuadraticKernel,:GammaRationalQuadraticKernel]
     @eval begin
         @inline (κ::$k)(d::Real) = kappa(κ,d) #TODO Add test
-        @inline (κ::$k)(x::AbstractVector{<:Real},y::AbstractVector{<:Real}) = kappa(κ,evaluate(metric(κ),transform(κ,x),transform(κ,y)))
+        @inline (κ::$k)(x::AbstractVector{<:Real}, y::AbstractVector{<:Real}) = kappa(κ, x, y)
         @inline (κ::$k)(X::AbstractMatrix{T},Y::AbstractMatrix{T};obsdim::Integer=defaultobs) where {T} = kernelmatrix(κ,X,Y,obsdim=obsdim)
         @inline (κ::$k)(X::AbstractMatrix{T};obsdim::Integer=defaultobs) where {T} = kernelmatrix(κ,X,obsdim=obsdim)
     end