add signrank distribution

src/StatsFuns.jl

@@ -219,6 +219,18 @@ export
     tdistinvlogcdf,     # inverse-logcdf of student's t distribution
     tdistinvlogccdf,    # inverse-logccdf of student's t distribution
 
+    # distrs/signrank
+    signrankpdf,
+    signranklogpdf,
+    signrankcdf,
+    signranklogcdf,
+    signrankccdf,
+    signranklogccdf,
+    signrankinvcdf,
+    signrankinvccdf,
+    signrankinvlogcdf,
+    signrankinvlogccdf,
+
     # distrs/srdist
     srdistcdf,           # cdf of studentized range distribution
     srdistccdf,          # ccdf of studentized range distribution
@@ -258,6 +270,7 @@ include(joinpath("distrs", "norm.jl"))
 include(joinpath("distrs", "ntdist.jl"))
 include(joinpath("distrs", "pois.jl"))
 include(joinpath("distrs", "tdist.jl"))
+include(joinpath("distrs", "signrank.jl"))
 include(joinpath("distrs", "srdist.jl"))
 
 if !isdefined(Base, :get_extension)

src/distrs/signrank.jl

@@ -0,0 +1,97 @@
+#=
+The signrank distribution is equivalent to the problem
+of finding the number of subsets of {1,2,...,n} summing to W,
+relative to the total number of subsets.
+The empty subset is defined to sum to zero.
+This can be calculated using the recursion:
+either n is in the subset in which case we need to calculate
+the number of subsets of {1,2,...,n-1} summing to W-n,
+or n is not in the subset in which case we need to calculate
+the number of subsets of {1,2,...,n-1} summing to W.
+This can be calculated bottom up using dynamic programming.
+
+The i'th element of DP in the j'th outer loop iteration represents:
+the number of ways {1,2,...,j} can sum to W-i+1.
+ =#
+
+@inline function signrankDP(n, W)
+    DP = zeros(Int, W + 1)
+    DP[W+1] = 1
+    for j in 1:n
+        for i in 1:(W+1-j)
+            DP[i] += DP[i+j]
+        end
+    end
+    return DP
+end
+
+function signrankpdf(n::Int, W::Union{Float64,Int})
+    W = round(Int, W)
+    max_W = (n * (n + 1)) >> 1
+    if W < 0
+        return 0.0
+    elseif W > max_W >> 1
+        return signrankpdf(n, max_W - W)
+    end
+    DP = signrankDP(n, W)
+    return ldexp(float(DP[1]), -n)
+end
+
+function signranklogpdf(n::Int, W::Union{Float64,Int})
+    return log(signrankpdf(n, W))
+end
+
+function signrankcdf(n::Int, W::Union{Float64,Int})
+    W = round(Int, W)
+    max_W = (n * (n + 1)) >> 1
+    if W < 0
+        return 0.0
+    elseif W > max_W >> 1
+        return 1.0 - signrankcdf(n, max_W - W - 1)
+    end
+    DP = signrankDP(n, W)
+    return sum(Base.Fix2(ldexp, -n) ∘ float, DP)
+end
+
+function signranklogcdf(n::Int, W::Union{Float64,Int})
+    return log(signrankcdf(n, W))
+end
+
+function signrankccdf(n::Int, W::Union{Float64,Int})
+    max_W = (n * (n + 1)) >> 1
+    return signrankcdf(n, max_W - W - 1, )
+end
+
+function signranklogccdf(n::Int, W::Union{Float64,Int})
+    return log(signrankccdf(n, W))
+end
+
+function signrankinvcdf(n::Int, p::Float64)
+    if p < 0.0 || p > 1.0
+        return NaN
+    end
+    W = 0
+    while signrankcdf(n, W) < p # TODO binary search and symmetry
+        W += 1
+    end
+    return float(W)
+end
+
+function signrankinvlogcdf(n::Int, logp::Float64)
+    if logp > 0.0
+        return NaN
+    end
+    W = 0
+    while signranklogcdf(n, W) < logp # TODO binary search and symmetry
+        W += 1
+    end
+    return float(W)
+end
+
+function signrankinvccdf(n::Int, p::Float64)
+    signrankinvcdf(n, 1 - p)
+end
+
+function signrankinvlogccdf(n::Int, logp::Float64)
+    signrankinvlogcdf(n, log1mexp(logp))
+end

src/rmath.jl

@@ -131,6 +131,7 @@ end
 
 ### Import specific functions
 
+@import_rmath signrank signrank n
 @import_rmath beta beta α β
 @import_rmath binom binom n p
 @import_rmath chisq chisq k

test/rmath.jl

@@ -215,6 +215,12 @@ end
             @test @inferred(betainvccdf(α, 0, p)) === 1f0
         end
     end
+
+    rmathcomp_tests("signrank", [
+        ((4),-2:12),
+        ((10),-2:57),
+#=         ((50),-2:1277), =#
+    ])
 
     rmathcomp_tests("binom", [
         ((1, 0.5), 0.0:1.0),