ZigZag sampler with a Soss model

zigzag-soss.jl

using Soss
using ZigZagBoomerang
using Soss: logdensity, xform, ConditionalModel
using ForwardDiff
using ForwardDiff: gradient!
using LinearAlgebra
using SparseArrays
using StructArrays
using TransformVariables
using MeasureTheory
using TupleVectors

Soss.xform(m::SpikeMixture) = Soss.xform(m.m)


function partiali(f,d)
    id = collect(I(d))
    ith(i) = @inbounds @view id[:,i]
    function (x,i)
        sa = StructArray{ForwardDiff.Dual{}}((x, ith(i)))
        δ = f(sa).partials[]
        return δ
    end
end


function zigzag(ℓ, t0, x0, v0, T=1000.0; c=10.0, adapt=false)
    d = length(x0)
    ∇ϕi = partiali(ℓ, d)
    pdmp(∇ϕi, t0, x0, v0, T, c*ones(d), ZigZag(sparse(I(d)), 0*x0); adapt=adapt)
end


m = @model x begin
    α ~ Normal()
    β ~ Normal()
    yhat = α .+ β .* x
    y ~ For(eachindex(x)) do j
        Normal(yhat[j], 2.0)
    end
end



x = randn(20);
obs = -0.1 .+ 2x + 1randn(20); 
post = m(x=x) | (y=obs,)

t = xform(post)

function ℓ(x)
    (θ, logjac) = TransformVariables.transform_and_logjac(t, x)
    -logdensity(post, θ) - logjac
end


tkeys = keys(t.transformations)
vars = Soss.select(simulate(post).trace, tkeys)

t0 = 0.0
x0 = inverse(t, vars)
v0 = randn(dimension(t))



T = 1000.0
mytrace, final, (num, acc) = zigzag(ℓ, t0, x0, v0, 100; c=20.0);

# mytrace is a continous object, discretize to obtain samples
ts, xs = ZigZagBoomerang.sep(discretize(mytrace, 0.1));

samples = TupleVector(xform(post).(xs))

using Plots


p = plot(ts, samples.α, label="α")
plot!(p, ts, samples.β, color=:red, label="β")

using TupleVectors: unwrap

# Unwrap a TupleVector to treat is as a NamedTuple of Vectors
p2 = @with unwrap(samples) begin
    plot(α, β, legend=false)
end

Hi Chad,

Thanks a lot for your quick answer.

Following your remark, I wrote:

samples = TupleVector(TransformVariables.transform.(xform(post),xs))

and it worked :)

All this seems very interesting, but I need some work for a better understanding :)

Best,
VP

👍