ConstantKernel Performance (#432)

* Add methods

* Bump patch version

* Use Fill

* Update src/basekernels/constant.jl

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

* Revert to fill

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: willtebbutt

Project.toml

@@ -1,6 +1,6 @@
 name = "KernelFunctions"
 uuid = "ec8451be-7e33-11e9-00cf-bbf324bd1392"
-version = "0.10.29"
+version = "0.10.30"
 
 [deps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"

src/basekernels/constant.jl

@@ -77,4 +77,12 @@ kappa(κ::ConstantKernel, x::Real) = only(κ.c) * one(x)
 
 metric(::ConstantKernel) = Delta()
 
+function kernelmatrix(k::ConstantKernel, x::AbstractVector)
+    return fill(only(k.c), length(x), length(x))
+end
+
+function kernelmatrix(k::ConstantKernel, x::AbstractVector, y::AbstractVector)
+    return fill(only(k.c), length(x), length(y))
+end
+
 Base.show(io::IO, κ::ConstantKernel) = print(io, "Constant Kernel (c = ", only(κ.c), ")")