Merge pull request #376 from SouthEndMusic/fix_ConstantInterpolationExtrapolation

Fix `ConstantInterpolation` integer extrapolation

Author: ChrisRackauckas

src/derivatives.jl

@@ -159,11 +159,11 @@ function _derivative(A::ConstantInterpolation, t::Number, iguess)
 end
 
 function _derivative(A::ConstantInterpolation{<:AbstractVector}, t::Number, iguess)
-    return isempty(searchsorted(A.t, t)) ? zero(A.u[1]) : eltype(A.u)(NaN)
+    return isempty(searchsorted(A.t, t)) ? zero(A.u[1]) : typed_nan(A.u)
 end
 
 function _derivative(A::ConstantInterpolation{<:AbstractMatrix}, t::Number, iguess)
-    return isempty(searchsorted(A.t, t)) ? zero(A.u[:, 1]) : eltype(A.u)(NaN) .* A.u[:, 1]
+    return isempty(searchsorted(A.t, t)) ? zero(A.u[:, 1]) : typed_nan(A.u) .* A.u[:, 1]
 end
 
 # QuadraticSpline Interpolation

src/interpolation_methods.jl

@@ -14,7 +14,7 @@ function _extrapolate_left(A, t)
         throw(LeftExtrapolationError())
     elseif extrapolation_left == ExtrapolationType.Constant
         slope = derivative(A, first(A.t))
-        first(A.u) + slope * zero(t)
+        first(A.u) + zero(slope * t)
     elseif extrapolation_left == ExtrapolationType.Linear
         slope = derivative(A, first(A.t))
         first(A.u) + slope * (t - first(A.t))
@@ -36,7 +36,7 @@ function _extrapolate_right(A, t)
         throw(RightExtrapolationError())
     elseif extrapolation_right == ExtrapolationType.Constant
         slope = derivative(A, last(A.t))
-        last(A.u) + slope * zero(t)
+        last(A.u) + zero(slope * t)
     elseif extrapolation_right == ExtrapolationType.Linear
         slope = derivative(A, last(A.t))
         last(A.u) + slope * (t - last(A.t))

src/interpolation_utils.jl

@@ -327,3 +327,6 @@ function transformation_reflective(A, t)
     (n > 0) && (n -= 1)
     t_, n
 end
+
+typed_nan(::AbstractArray{T}) where {T <: AbstractFloat} = T(NaN)
+typed_nan(::AbstractArray{T}) where {T <: Integer} = zero(T)

test/interpolation_tests.jl

@@ -520,6 +520,10 @@ end
     A = ConstantInterpolation(u, t; extrapolation = ExtrapolationType.Extension)
     @test A(Inf) == last(u)
     @test A(-Inf) == first(u)
+
+    # Test extrapolation of integer output
+    itp = ConstantInterpolation([2], [0.0]; extrapolation = ExtrapolationType.Constant)
+    @test itp(1.0) == 2
 end
 
 @testset "QuadraticSpline Interpolation" begin