Add RankUpdateEuclideanMetric

docs/src/api.md

@@ -8,6 +8,7 @@ This modularity means that different HMC variants can be easily constructed by c
   - Unit metric: `UnitEuclideanMetric(dim)`
   - Diagonal metric: `DiagEuclideanMetric(dim)`
   - Dense metric: `DenseEuclideanMetric(dim)`
+  - Rank update metric: `RankUpdateEuclideanMetric(dim)`
 
 where `dim` is the dimensionality of the sampling space.
 

src/AdvancedHMC.jl

@@ -2,7 +2,18 @@ module AdvancedHMC
 
 using Statistics: mean, var, middle
 using LinearAlgebra:
-    Symmetric, UpperTriangular, mul!, ldiv!, dot, I, diag, cholesky, UniformScaling
+    Symmetric,
+    UpperTriangular,
+    mul!,
+    ldiv!,
+    dot,
+    I,
+    diag,
+    cholesky,
+    UniformScaling,
+    Diagonal,
+    qr,
+    lmul!
 using StatsFuns: logaddexp, logsumexp, loghalf
 using Random: Random, AbstractRNG
 using ProgressMeter: ProgressMeter
@@ -40,7 +51,8 @@ struct GaussianKinetic <: AbstractKinetic end
 export GaussianKinetic
 
 include("metric.jl")
-export UnitEuclideanMetric, DiagEuclideanMetric, DenseEuclideanMetric
+export UnitEuclideanMetric,
+    DiagEuclideanMetric, DenseEuclideanMetric, RankUpdateEuclideanMetric
 
 include("hamiltonian.jl")
 export Hamiltonian

src/hamiltonian.jl

@@ -61,6 +61,18 @@ function ∂H∂r(h::Hamiltonian{<:DenseEuclideanMetric,<:GaussianKinetic}, r::A
     return M⁻¹ * r
 end
 
+function ∂H∂r(
+    h::Hamiltonian{<:RankUpdateEuclideanMetric,<:GaussianKinetic}, r::AbstractVecOrMat
+)
+    (; M⁻¹) = h.metric
+    axes_M⁻¹ = __axes(M⁻¹)
+    axes_r = __axes(r)
+    (first(axes_M⁻¹) !== first(axes_r)) && throw(
+        ArgumentError("AxesMismatch: M⁻¹ has axes $(axes_M⁻¹) but r has axes $(axes_r)")
+    )
+    return M⁻¹ * r
+end
+
 # TODO (kai) make the order of θ and r consistent with neg_energy
 # TODO (kai) add stricter types to block hamiltonian.jl#L37 from working on unknown metric/kinetic
 # The gradient of a position-dependent Hamiltonian system depends on both θ and r. 
@@ -165,6 +177,13 @@ function neg_energy(
     return -dot(r, h.metric._temp) / 2
 end
 
+function neg_energy(
+    h::Hamiltonian{<:RankUpdateEuclideanMetric,<:GaussianKinetic}, r::T, θ::T
+) where {T<:AbstractVecOrMat}
+    M⁻¹ = h.metric.M⁻¹
+    return -r' * M⁻¹ * r / 2
+end
+
 energy(args...) = -neg_energy(args...)
 
 ####

src/metric.jl

@@ -98,6 +98,68 @@ function Base.show(io::IO, dem::DenseEuclideanMetric)
     return print(io, "DenseEuclideanMetric(diag=$(_string_M⁻¹(dem.M⁻¹)))")
 end
 
+"""
+    RankUpdateEuclideanMetric{T,M} <: AbstractMetric
+
+A Gaussian Euclidean metric whose inverse is constructed by rank-updates.
+
+# Constructors
+
+    RankUpdateEuclideanMetric(n::Int)
+
+Construct a Gaussian Euclidean metric of size `(n, n)` with inverse of `M⁻¹`.
+
+# Example
+
+```julia
+julia> RankUpdateEuclideanMetric(3)
+RankUpdateEuclideanMetric(diag=[1.0, 1.0, 1.0])
+```
+"""
+struct RankUpdateEuclideanMetric{T,AM<:AbstractVecOrMat{T},AB,AD,F} <: AbstractMetric
+    # Diagnal of the inverse of the mass matrix
+    M⁻¹::AM
+    B::AB
+    D::AD
+    factorization::F
+end
+
+function woodbury_factorize(A, B, D)
+    cholA = cholesky(A isa Diagonal ? A : Symmetric(A))
+    U = cholA.U
+    Q, R = qr(U' \ B)
+    V = cholesky(Symmetric(muladd(R, D * R', I))).U
+    return (U=U, Q=Q, V=V)
+end
+
+function RankUpdateEuclideanMetric(n::Int)
+    M⁻¹ = Diagonal(ones(n))
+    B = zeros(n, 0)
+    D = zeros(0, 0)
+    factorization = woodbury_factorize(M⁻¹, B, D)
+    return RankUpdateEuclideanMetric(M⁻¹, B, D, factorization)
+end
+function RankUpdateEuclideanMetric(::Type{T}, n::Int) where {T}
+    M⁻¹ = Diagonal(ones(T, n))
+    B = Matrix{T}(undef, n, 0)
+    D = Matrix{T}(undef, 0, 0)
+    factorization = woodbury_factorize(M⁻¹, B, D)
+    return RankUpdateEuclideanMetric(M⁻¹, B, D, factorization)
+end
+function RankUpdateEuclideanMetric(::Type{T}, sz::Tuple{Int}) where {T}
+    return RankUpdateEuclideanMetric(T, first(sz))
+end
+RankUpdateEuclideanMetric(sz::Tuple{Int}) = RankUpdateEuclideanMetric(Float64, sz)
+
+AdvancedHMC.renew(::RankUpdateEuclideanMetric, M⁻¹) = RankUpdateEuclideanMetric(M⁻¹)
+
+Base.size(metric::RankUpdateEuclideanMetric, dim...) = size(metric.M⁻¹.diag, dim...)
+
+function Base.show(io::IO, metric::RankUpdateEuclideanMetric)
+    print(io, "RankUpdateEuclideanMetric(diag=$(diag(metric.M⁻¹)))")
+    return nothing
+end
+
 # `rand` functions for `metric` types.
 
 function rand_momentum(
@@ -131,3 +193,19 @@ function rand_momentum(
     ldiv!(metric.cholM⁻¹, r)
     return r
 end
+
+function rand_momentum(
+    rng::Union{AbstractRNG,AbstractVector{<:AbstractRNG}},
+    metric::RankUpdateEuclideanMetric{T},
+    kinetic::GaussianKinetic,
+    ::AbstractVecOrMat,
+) where {T}
+    M⁻¹ = metric.M⁻¹
+    r = _randn(rng, T, size(M⁻¹.diag)...)
+    F = metric.factorization
+    k = min(size(F.U, 1), size(F.V, 1))
+    @views ldiv!(F.V, r isa AbstractVector ? r[1:k] : r[1:k, :])
+    lmul!(F.Q, r)
+    ldiv!(F.U, r)
+    return r
+end

test/metric.jl

@@ -10,6 +10,7 @@ using ReTest, Random, AdvancedHMC
             UnitEuclideanMetric((D, n_chains)),
             DiagEuclideanMetric((D, n_chains)),
             # DenseEuclideanMetric((D, n_chains)) # not supported ATM
+            # RankUpdateEuclideanMetric((D, n_chains)) # not supported ATM
         ]
             r = AdvancedHMC.rand_momentum(rng, metric, GaussianKinetic(), θ)
             all_same = true
@@ -25,8 +26,12 @@ using ReTest, Random, AdvancedHMC
         rng = MersenneTwister(1)
         θ = randn(rng, D)
         ℓπ(θ) = 1
-        for metric in
-            [UnitEuclideanMetric(1), DiagEuclideanMetric(1), DenseEuclideanMetric(1)]
+        for metric in [
+            UnitEuclideanMetric(1),
+            DiagEuclideanMetric(1),
+            DenseEuclideanMetric(1),
+            RankUpdateEuclideanMetric(1),
+        ]
             h = Hamiltonian(metric, ℓπ, ℓπ)
             h = AdvancedHMC.resize(h, θ)
             @test size(h.metric) == size(θ)