Merge branch 'master' into fix-periodic

Author: simsurace

Project.toml

@@ -1,6 +1,6 @@
 name = "KernelFunctions"
 uuid = "ec8451be-7e33-11e9-00cf-bbf324bd1392"
-version = "0.10.58"
+version = "0.10.59"
 
 [deps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"
@@ -32,6 +32,7 @@ IrrationalConstants = "0.1, 0.2"
 LogExpFunctions = "0.2.1, 0.3"
 Requires = "1.0.1"
 SpecialFunctions = "0.8, 0.9, 0.10, 1, 2"
+Statistics = "1"
 StatsBase = "0.32, 0.33, 0.34"
 TensorCore = "0.1"
 ZygoteRules = "0.2"

docs/Project.toml

@@ -12,4 +12,5 @@ Documenter = "0.27"
 KernelFunctions = "0.10"
 Kronecker = "0.4, 0.5"
 PDMats = "0.11"
+Statistics = "1"
 julia = "1.3"

src/basekernels/matern.jl

@@ -41,7 +41,8 @@ MaternKernel(; nu::Real=1.5, ν::Real=nu, metric=Euclidean()) = MaternKernel(ν,
 
 function _matern(ν::Real, d::Real)
     if iszero(d)
-        return one(d)
+        c = -ν / (ν - 1)
+        return one(d) + c * d^2 / 2
     else
         y = sqrt(2ν) * d
         b = log(besselk(ν, y))

test/Project.toml

@@ -36,4 +36,5 @@ ReverseDiff = "1.2"
 SpecialFunctions = "0.10, 1, 2"
 StableRNGs = "1"
 StaticArrays = "1"
+Statistics = "1"
 Zygote = "0.6.38"