Add ChangesOfVariables definitions and extend tests

ext/LogExpFunctionsChangesOfVariablesExt.jl

@@ -8,11 +8,25 @@ function ChangesOfVariables.with_logabsdet_jacobian(::typeof(log1pexp), x::Real)
     y = log1pexp(x)
     return y, x - y
 end
+function ChangesOfVariables.with_logabsdet_jacobian(::typeof(softplus), x::Real)
+    return ChangesOfVariables.with_logabsdet_jacobian(log1pexp, x)
+end
+function ChangesOfVariables.with_logabsdet_jacobian(f::Base.Fix2{typeof(softplus),<:Real}, x::Real)
+    y = f(x)
+    return y, f.x * (x - y)
+end
 
 function ChangesOfVariables.with_logabsdet_jacobian(::typeof(logexpm1), x::Real)
     y = logexpm1(x)
     return y, x - y
 end
+function ChangesOfVariables.with_logabsdet_jacobian(::typeof(invsoftplus), x::Real)
+    return ChangesOfVariables.with_logabsdet_jacobian(logexpm1, x)
+end
+function ChangesOfVariables.with_logabsdet_jacobian(f::Base.Fix2{typeof(invsoftplus),<:Real}, x::Real)
+    y = f(x)
+    return y, f.x * (x - y)
+end
 
 function ChangesOfVariables.with_logabsdet_jacobian(::typeof(log1mexp), x::Real)
     y = log1mexp(x)

ext/LogExpFunctionsInverseFunctionsExt.jl

@@ -23,6 +23,13 @@ InverseFunctions.inverse(::typeof(log1mlogistic)) = logit1mexp
 InverseFunctions.inverse(::typeof(logit1mexp)) = log1mlogistic
 
 InverseFunctions.inverse(::typeof(softplus)) = invsoftplus
+function InverseFunctions.inverse(f::Base.Fix2{typeof(softplus),<:Real})
+    Base.Fix2(invsoftplus, f.x)
+end
+
 InverseFunctions.inverse(::typeof(invsoftplus)) = softplus
+function InverseFunctions.inverse(f::Base.Fix2{typeof(invsoftplus),<:Real})
+    Base.Fix2(softplus, f.x)
+end
 
 end # module

test/basicfuns.jl

@@ -162,13 +162,15 @@ end
 end
 
 @testset "softplus" begin
-    @test softplus(2) ≈ log1pexp(2)
-    @test softplus(2, 1) ≈ log1pexp(2)
-    @test softplus(2, 10) < log1pexp(2)
-    @test invsoftplus(softplus(2), 1) ≈ 2
+    for T in (Int, Float64, Float32, Float16)
+        @test @inferred(softplus(T(2))) === log1pexp(T(2))
+        @test @inferred(softplus(T(2), 1)) isa float(T)
+        @test @inferred(softplus(T(2), 1)) ≈ softplus(T(2))
+        @test @inferred(softplus(T(2), 5)) ≈ softplus(5 * T(2)) / 5
+        @test @inferred(softplus(T(2), 10)) ≈ softplus(10 * T(2)) / 10
+    end
 end
 
-
 @testset "log1mexp" begin
     for T in (Float64, Float32, Float16)
         @test @inferred(log1mexp(-T(1))) isa T
@@ -194,6 +196,16 @@ end
     end
 end
 
+@testset "invsoftplus" begin
+    for T in (Int, Float64, Float32, Float16)
+        @test @inferred(invsoftplus(T(2))) === logexpm1(T(2))
+        @test @inferred(invsoftplus(T(2), 1)) isa float(T)
+        @test @inferred(invsoftplus(T(2), 1)) ≈ invsoftplus(T(2))
+        @test @inferred(invsoftplus(T(2), 5)) ≈ invsoftplus(5 * T(2)) / 5
+        @test @inferred(invsoftplus(T(2), 10)) ≈ invsoftplus(10 * T(2)) / 10
+    end
+end
+
 @testset "log1pmx" begin
     @test iszero(log1pmx(0.0))
     @test log1pmx(1.0) ≈ log(2.0) - 1.0

test/inverse.jl

@@ -1,6 +1,11 @@
 @testset "inverse.jl" begin
     InverseFunctions.test_inverse(log1pexp, randn())
+    InverseFunctions.test_inverse(softplus, randn())
+    InverseFunctions.test_inverse(Base.Fix2(softplus, randexp()), randn())
+
     InverseFunctions.test_inverse(logexpm1, randexp())
+    InverseFunctions.test_inverse(invsoftplus, randexp())
+    InverseFunctions.test_inverse(Base.Fix2(invsoftplus, randexp()), randexp())
 
     InverseFunctions.test_inverse(log1mexp, -randexp())
 
@@ -17,7 +22,4 @@
 
     InverseFunctions.test_inverse(log1mlogistic, randexp())
     InverseFunctions.test_inverse(logit1mexp, -randexp())
-
-    InverseFunctions.test_inverse(softplus, randn())
-    InverseFunctions.test_inverse(invsoftplus, randexp())
 end

test/with_logabsdet_jacobian.jl

@@ -1,12 +1,23 @@
 @testset "with_logabsdet_jacobian" begin
     derivative(f, x) = ChainRulesTestUtils.frule((ChainRulesTestUtils.NoTangent(), 1), f, x)[2]
+    derivative(::typeof(softplus), x) = derivative(log1pexp, x)
+    derivative(f::Base.Fix2{typeof(softplus),<:Real}, x) = derivative(log1pexp, f.x * x)
+    derivative(::typeof(invsoftplus), x) = derivative(logexpm1, x)
+    derivative(f::Base.Fix2{typeof(invsoftplus),<:Real}, x) = derivative(logexpm1, f.x * x)
 
     x = randexp()
+    y = randexp()
 
     ChangesOfVariables.test_with_logabsdet_jacobian(log1pexp, x, derivative)
     ChangesOfVariables.test_with_logabsdet_jacobian(log1pexp, -x, derivative)
+    ChangesOfVariables.test_with_logabsdet_jacobian(softplus, x, derivative)
+    ChangesOfVariables.test_with_logabsdet_jacobian(softplus, -x, derivative)
+    ChangesOfVariables.test_with_logabsdet_jacobian(Base.Fix2(softplus, y), x, derivative)
+    ChangesOfVariables.test_with_logabsdet_jacobian(Base.Fix2(softplus, y), -x, derivative)
 
     ChangesOfVariables.test_with_logabsdet_jacobian(logexpm1, x, derivative)
+    ChangesOfVariables.test_with_logabsdet_jacobian(invsoftplus, x, derivative)
+    ChangesOfVariables.test_with_logabsdet_jacobian(Base.Fix2(invsoftplus, y), x, derivative)
 
     ChangesOfVariables.test_with_logabsdet_jacobian(log1mexp, -x, derivative)