Ensure that the interpolation domain is sorted

ext/DataInterpolationsRegularizationToolsExt.jl

@@ -76,7 +76,7 @@ function RegularizationSmooth(u::AbstractVector, t::AbstractVector, t̂::Abstrac
         cache_parameters::Bool = false)
     extrapolation_left, extrapolation_right = munge_extrapolation(
         extrapolation, extrapolation_left, extrapolation_right)
-    u, t = munge_data(u, t)
+    u, t = munge_data(u, t; check_sorted = t̂, sorted_arg_name = ("third", "t̂"))
     M = _mapping_matrix(t̂, t)
     Wls½ = LA.diagm(sqrt.(wls))
     Wr½ = LA.diagm(sqrt.(wr))
@@ -139,7 +139,7 @@ function RegularizationSmooth(u::AbstractVector, t::AbstractVector, t̂::Abstrac
         cache_parameters::Bool = false)
     extrapolation_left, extrapolation_right = munge_extrapolation(
         extrapolation, extrapolation_left, extrapolation_right)
-    u, t = munge_data(u, t)
+    u, t = munge_data(u, t; check_sorted = t̂, sorted_arg_name = ("third", "t̂"))
     N, N̂ = length(t), length(t̂)
     M = _mapping_matrix(t̂, t)
     Wls½ = Array{Float64}(LA.I, N, N)
@@ -176,7 +176,7 @@ function RegularizationSmooth(u::AbstractVector, t::AbstractVector, t̂::Abstrac
         cache_parameters::Bool = false)
     extrapolation_left, extrapolation_right = munge_extrapolation(
         extrapolation, extrapolation_left, extrapolation_right)
-    u, t = munge_data(u, t)
+    u, t = munge_data(u, t; check_sorted = t̂, sorted_arg_name = ("third", "t̂"))
     N, N̂ = length(t), length(t̂)
     M = _mapping_matrix(t̂, t)
     Wls½ = LA.diagm(sqrt.(wls))

src/interpolation_utils.jl

@@ -91,14 +91,26 @@ function quadratic_spline_params(t::AbstractVector, sc::AbstractVector)
 end
 
 # helper function for data manipulation
-function munge_data(u::AbstractVector, t::AbstractVector)
+function munge_data(u::AbstractVector, t::AbstractVector;
+        check_sorted = t, sorted_arg_name = ("second", "t"))
     Tu = nonmissingtype(eltype(u))
     Tt = nonmissingtype(eltype(t))
+
     if Tu === eltype(u) && Tt === eltype(t)
+        if !issorted(check_sorted)
+            # there is likely an user error
+            msg = "The $(sorted_arg_name[1]) argument (`$(sorted_arg_name[2])`), which is used for the interpolation domain, is not sorted."
+            if issorted(u)
+                msg *= "\nIt looks like the arguments `u` and `$(sorted_arg_name[2])` were inversed, make sure you used the arguments in the correct order."
+            end
+            throw(ArgumentError(msg))
+        end
+
         return u, t
     end
 
     @assert length(t) == length(u)
+
     non_missing_mask = map((ui, ti) -> !ismissing(ui) && !ismissing(ti), u, t)
     u = convert(AbstractVector{Tu}, u[non_missing_mask])
     t = convert(AbstractVector{Tt}, t[non_missing_mask])

test/interpolation_tests.jl

@@ -1105,3 +1105,8 @@ f_cubic_spline = c -> square(CubicSpline, c)
         end
     end
 end
+
+@testset "user error" begin
+    @test_throws ArgumentError LinearInterpolation(rand(10), rand(10))
+    @test_throws ArgumentError LinearInterpolation(0:10, rand(10))
+end

test/regularization.jl

@@ -191,3 +191,10 @@ end
     A = RegularizationSmooth(uₒ, tₒ; alg = :fixed)
     @test @inferred(A(1.0)) == A(1.0)
 end
+
+@testset "User error" begin
+    @test_throws ArgumentError RegularizationSmooth(tₒ, uₒ; alg = :fixed)
+    N̂ = 20
+    t̂ = collect(range(xmin, xmin + xspan, length = N̂))
+    @test_throws ArgumentError RegularizationSmooth(u, t̂, t)
+end