make mean(::Chi) more robust (#1305)

JuliaStats · Apr 20, 2021 · 093e876 · 093e876
1 parent df5aee3
commit 093e876
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diff --git a/src/univariate/continuous/chi.jl b/src/univariate/continuous/chi.jl
@@ -48,7 +48,7 @@ params(d::Chi) = (d.ν,)
 
 #### Statistics
 
-mean(d::Chi) = (h = d.ν/2; sqrt2 * gamma(h + 1//2) / gamma(h))
+mean(d::Chi) = (h = d.ν/2; sqrt2 * exp(loggamma(h + 1//2) - loggamma(h)))
 
 var(d::Chi) = d.ν - mean(d)^2
 _chi_skewness(μ::Real, σ::Real) = (σ2 = σ^2; σ3 = σ2 * σ; (μ / σ3) * (1 - 2σ2))

diff --git a/test/chi.jl b/test/chi.jl
@@ -0,0 +1,2 @@
+# see #1305
+@test isfinite(mean(Chi(1000)))
diff --git a/test/runtests.jl b/test/runtests.jl
@@ -60,6 +60,7 @@ const tests = [
     "bernoulli",
     "soliton",
     "skewnormal",
+    "chi",
 ]
 
 printstyled("Running tests:\n", color=:blue)