add Matern12Kernel as alias for ExponentialKernel

Author: st--

docs/src/kernels.md

@@ -116,7 +116,7 @@ The Matérn 1/2 kernel is defined as
 ```math
   k(x,x') = \exp\left(-|x-x'|\right),
 ```
-equivalent to the Exponential kernel. There is no `Matern12Kernel`, use [`ExponentialKernel`](@ref) instead.
+equivalent to the Exponential kernel. `Matern12Kernel` is an alias for [`ExponentialKernel`](@ref).
 
 ### Matérn 3/2 Kernel
 

src/basekernels/exponential.jl

@@ -42,8 +42,9 @@ iskroncompatible(::ExponentialKernel) = true
 
 Base.show(io::IO, ::ExponentialKernel) = print(io, "Exponential Kernel")
 
-## Alias ##
+## Aliases ##
 const LaplacianKernel = ExponentialKernel
+const Matern12Kernel = ExponentialKernel
 
 """
     GammaExponentialKernel(; γ = 2.0)

src/basekernels/matern.jl

@@ -33,6 +33,8 @@ metric(::MaternKernel) = Euclidean()
 
 Base.show(io::IO, κ::MaternKernel) = print(io, "Matern Kernel (ν = ", first(κ.ν), ")")
 
+## Matern12Kernel = ExponentialKernel aliased in exponential.jl
+
 """
     Matern32Kernel()
 

src/transform/lineartransform.jl

@@ -9,7 +9,6 @@ The second dimension of `A` must match the number of features of the target.
 
 ```julia-repl
 julia> A = rand(10, 5)
-
 julia> tr = LinearTransform(A)
 ```
 """