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Fix #281: Fix sampler failure when n_samples = 1 #489

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Fix #281: Fix sampler failure when n_samples = 1 #489

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3 changes: 2 additions & 1 deletion src/sampler.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -228,12 +228,13 @@ function sample(
end
# Report end of sampling
if verbose
EBFMI_est = EBFMI(map(s -> s.hamiltonian_energy, stats))
average_acceptance_rate = mean(map(s -> s.acceptance_rate, stats))
if θ isa AbstractVector
n_chains = 1
EBFMI_est = length(stats) > 1 ? EBFMI(map(s -> s.hamiltonian_energy, stats)) : NaN
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@github-actions github-actions bot Mar 19, 2026

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[JuliaFormatter] reported by reviewdog 🐶

Suggested change
EBFMI_est = length(stats) > 1 ? EBFMI(map(s -> s.hamiltonian_energy, stats)) : NaN
EBFMI_est =
length(stats) > 1 ? EBFMI(map(s -> s.hamiltonian_energy, stats)) : NaN

else
n_chains = size(θ, 2)
EBFMI_est = length(stats) > 1 ? EBFMI(map(s -> s.hamiltonian_energy, stats)) : fill(NaN, n_chains)
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[JuliaFormatter] reported by reviewdog 🐶

Suggested change
EBFMI_est = length(stats) > 1 ? EBFMI(map(s -> s.hamiltonian_energy, stats)) : fill(NaN, n_chains)
EBFMI_est = if length(stats) > 1
EBFMI(map(s -> s.hamiltonian_energy, stats))
else
fill(NaN, n_chains)
end

# Make sure that arrays are on CPU before printing.
EBFMI_est = convert(Vector{eltype(EBFMI_est)}, EBFMI_est)
average_acceptance_rate = convert(
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11 changes: 11 additions & 0 deletions test/sampler.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -180,3 +180,14 @@ end
@test length(stats) == n_samples
end
end

@testset "n_samples=1 does not crash" begin
# Regression test for https://github.com/TuringLang/AdvancedHMC.jl/issues/281
# verbose=true triggers EBFMI computation which failed on a 1-element stats vector
θ_init = rand(MersenneTwister(1), D)
h = Hamiltonian(DiagEuclideanMetric(D), ℓπ, ∂ℓπ∂θ)
κ = HMCKernel(Trajectory{MultinomialTS}(Leapfrog(0.1), GeneralisedNoUTurn()))
samples, stats = sample(h, κ, θ_init, 1; verbose=true, progress=false)
@test length(samples) == 1
@test length(stats) == 1
end
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