Fix input types, improve readability (#369)

* Fix input types, improve readability * Add missing bit * Add doc string * Fix mistake * Add docstring to docs * Reformulate * Bump version * Update src/matrix/kernelkroneckermat.jl Co-authored-by: Théo Galy-Fajou <theo.galyfajou@gmail.com> * Bump version further, rename api section * Apply format suggestions from code review Co-authored-by: willtebbutt <wt0881@my.bristol.ac.uk> * Improve error handling. Co-authored-by: st-- <st--@users.noreply.github.com> * Formatter Co-authored-by: Théo Galy-Fajou <theo.galyfajou@gmail.com> Co-authored-by: willtebbutt <wt0881@my.bristol.ac.uk> Co-authored-by: st-- <st--@users.noreply.github.com>
JuliaGaussianProcesses · Sep 29, 2021 · 6e7ca17 · 6e7ca17 · Crown421 · Sep 29, 2021
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diff --git a/Project.toml b/Project.toml
@@ -1,6 +1,6 @@
 name = "KernelFunctions"
 uuid = "ec8451be-7e33-11e9-00cf-bbf324bd1392"
-version = "0.10.19"
+version = "0.10.20"
 
 [deps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"

diff --git a/docs/src/api.md b/docs/src/api.md
@@ -88,3 +88,12 @@ kernelpdmat
 nystrom
 NystromFact
 ```
+
+## Conditional Utilities
+To keep the dependencies of KernelFunctions lean, some functionality is only available if specific other packages are explicitly loaded (`using`).
+
+### Kronecker.jl
+[*https://github.com/MichielStock/Kronecker.jl*](https://github.com/MichielStock/Kronecker.jl)
+```@docs
+kronecker_kernelmatrix
+```
diff --git a/src/matrix/kernelkroneckermat.jl b/src/matrix/kernelkroneckermat.jl
@@ -27,31 +27,43 @@ end
 """
 @inline iskroncompatible(κ::Kernel) = false # Default return for kernels
 
-function _kernelmatrix_kroneckerjl_helper(::MOInputIsotopicByFeatures, Kfeatures, Koutputs)
+function _kernelmatrix_kroneckerjl_helper(
+    ::Type{<:MOInputIsotopicByFeatures}, Kfeatures, Koutputs
+)
     return Kronecker.kronecker(Kfeatures, Koutputs)
 end
 
-function _kernelmatrix_kroneckerjl_helper(::MOInputIsotopicByOutputs, Kfeatures, Koutputs)
+function _kernelmatrix_kroneckerjl_helper(
+    ::Type{<:MOInputIsotopicByOutputs}, Kfeatures, Koutputs
+)
     return Kronecker.kronecker(Koutputs, Kfeatures)
 end
 
+"""
+    kronecker_kernelmatrix(
+        k::Union{IndependentMOKernel,IntrinsicCoregionMOKernel}, x::MOI, y::MOI
+    ) where {MOI<:IsotopicMOInputsUnion}
+
+Requires Kronecker.jl: Computes the `kernelmatrix` for the `IndependentMOKernel` and the
+`IntrinsicCoregionMOKernel`, but returns a lazy kronecker product. This object can be very
+efficiently inverted or decomposed. See also [`kernelmatrix`](@ref).
+"""
 function kronecker_kernelmatrix(
-    k::Union{IndependentMOKernel,IntrinsicCoregionMOKernel},
-    x::IsotopicMOInputsUnion,
-    y::IsotopicMOInputsUnion,
-)
-    @assert x.out_dim == y.out_dim
+    k::Union{IndependentMOKernel,IntrinsicCoregionMOKernel}, x::MOI, y::MOI
+) where {MOI<:IsotopicMOInputsUnion}
+    x.out_dim == y.out_dim ||
+        throw(DimensionMismatch("`x` and `y` must have the same `out_dim`"))
     Kfeatures = kernelmatrix(k.kernel, x.x, y.x)
     Koutputs = _mo_output_covariance(k, x.out_dim)
-    return _kernelmatrix_kroneckerjl_helper(x, Kfeatures, Koutputs)
+    return _kernelmatrix_kroneckerjl_helper(MOI, Kfeatures, Koutputs)
 end
 
 function kronecker_kernelmatrix(
-    k::Union{IndependentMOKernel,IntrinsicCoregionMOKernel}, x::IsotopicMOInputsUnion
-)
+    k::Union{IndependentMOKernel,IntrinsicCoregionMOKernel}, x::MOI
+) where {MOI<:IsotopicMOInputsUnion}
     Kfeatures = kernelmatrix(k.kernel, x.x)
     Koutputs = _mo_output_covariance(k, x.out_dim)
-    return _kernelmatrix_kroneckerjl_helper(x, Kfeatures, Koutputs)
+    return _kernelmatrix_kroneckerjl_helper(MOI, Kfeatures, Koutputs)
 end
 
 function kronecker_kernelmatrix(

diff --git a/src/mokernels/independent.jl b/src/mokernels/independent.jl
@@ -30,25 +30,24 @@ end
 _mo_output_covariance(k::IndependentMOKernel, out_dim) = Eye{Bool}(out_dim)
 
 function kernelmatrix(
-    k::IndependentMOKernel, x::IsotopicMOInputsUnion, y::IsotopicMOInputsUnion
-)
-    @assert x.out_dim == y.out_dim
+    k::IndependentMOKernel, x::MOI, y::MOI
+) where {MOI<:IsotopicMOInputsUnion}
+    x.out_dim == y.out_dim ||
+        throw(DimensionMismatch("`x` and `y` must have the same `out_dim`"))
     Kfeatures = kernelmatrix(k.kernel, x.x, y.x)
     Koutputs = _mo_output_covariance(k, x.out_dim)
-    return _kernelmatrix_kron_helper(x, Kfeatures, Koutputs)
+    return _kernelmatrix_kron_helper(MOI, Kfeatures, Koutputs)
 end
 
 if VERSION >= v"1.6"
     function kernelmatrix!(
-        K::AbstractMatrix,
-        k::IndependentMOKernel,
-        x::IsotopicMOInputsUnion,
-        y::IsotopicMOInputsUnion,
-    )
-        @assert x.out_dim == y.out_dim
+        K::AbstractMatrix, k::IndependentMOKernel, x::MOI, y::MOI
+    ) where {MOI<:IsotopicMOInputsUnion}
+        x.out_dim == y.out_dim ||
+            throw(DimensionMismatch("`x` and `y` must have the same `out_dim`"))
         Kfeatures = kernelmatrix(k.kernel, x.x, y.x)
         Koutputs = _mo_output_covariance(k, x.out_dim)
-        return _kernelmatrix_kron_helper!(K, x, Kfeatures, Koutputs)
+        return _kernelmatrix_kron_helper!(K, MOI, Kfeatures, Koutputs)
     end
 end
 

diff --git a/src/mokernels/intrinsiccoregion.jl b/src/mokernels/intrinsiccoregion.jl
@@ -48,25 +48,24 @@ function _mo_output_covariance(k::IntrinsicCoregionMOKernel, out_dim)
 end
 
 function kernelmatrix(
-    k::IntrinsicCoregionMOKernel, x::IsotopicMOInputsUnion, y::IsotopicMOInputsUnion
-)
-    @assert x.out_dim == y.out_dim
+    k::IntrinsicCoregionMOKernel, x::MOI, y::MOI
+) where {MOI<:IsotopicMOInputsUnion}
+    x.out_dim == y.out_dim ||
+        throw(DimensionMismatch("`x` and `y` must have the same `out_dim`"))
     Kfeatures = kernelmatrix(k.kernel, x.x, y.x)
     Koutputs = _mo_output_covariance(k, x.out_dim)
-    return _kernelmatrix_kron_helper(x, Kfeatures, Koutputs)
+    return _kernelmatrix_kron_helper(MOI, Kfeatures, Koutputs)
 end
 
 if VERSION >= v"1.6"
     function kernelmatrix!(
-        K::AbstractMatrix,
-        k::IntrinsicCoregionMOKernel,
-        x::IsotopicMOInputsUnion,
-        y::IsotopicMOInputsUnion,
-    )
-        @assert x.out_dim == y.out_dim
+        K::AbstractMatrix, k::IntrinsicCoregionMOKernel, x::MOI, y::MOI
+    ) where {MOI<:IsotopicMOInputsUnion}
+        x.out_dim == y.out_dim ||
+            throw(DimensionMismatch("`x` and `y` must have the same `out_dim`"))
         Kfeatures = kernelmatrix(k.kernel, x.x, y.x)
         Koutputs = _mo_output_covariance(k, x.out_dim)
-        return _kernelmatrix_kron_helper!(K, x, Kfeatures, Koutputs)
+        return _kernelmatrix_kron_helper!(K, MOI, Kfeatures, Koutputs)
     end
 end
 

diff --git a/src/mokernels/mokernel.jl b/src/mokernels/mokernel.jl
@@ -5,20 +5,24 @@ Abstract type for kernels with multiple outpus.
 """
 abstract type MOKernel <: Kernel end
 
-function _kernelmatrix_kron_helper(::MOInputIsotopicByFeatures, Kfeatures, Koutputs)
+function _kernelmatrix_kron_helper(::Type{<:MOInputIsotopicByFeatures}, Kfeatures, Koutputs)
     return kron(Kfeatures, Koutputs)
 end
 
-function _kernelmatrix_kron_helper(::MOInputIsotopicByOutputs, Kfeatures, Koutputs)
+function _kernelmatrix_kron_helper(::Type{<:MOInputIsotopicByOutputs}, Kfeatures, Koutputs)
     return kron(Koutputs, Kfeatures)
 end
 
 if VERSION >= v"1.6"
-    function _kernelmatrix_kron_helper!(K, ::MOInputIsotopicByFeatures, Kfeatures, Koutputs)
+    function _kernelmatrix_kron_helper!(
+        K, ::Type{<:MOInputIsotopicByFeatures}, Kfeatures, Koutputs
+    )
         return kron!(K, Kfeatures, Koutputs)
     end
 
-    function _kernelmatrix_kron_helper!(K, ::MOInputIsotopicByOutputs, Kfeatures, Koutputs)
+    function _kernelmatrix_kron_helper!(
+        K, ::Type{<:MOInputIsotopicByOutputs}, Kfeatures, Koutputs
+    )
         return kron!(K, Koutputs, Kfeatures)
     end
 end