fix(Unitful): find_zero on <:Quantity interval chooses Bisection method (#475)

* fix(Unitful): `find_zero` on `<:Quantity` interval chooses `Bisection` method

* fix(test): Test with `isapprox` instead of equivalence for round-off errors

Author: kunzaatko

Project.toml

@@ -14,13 +14,15 @@ ForwardDiff = "f6369f11-7733-5829-9624-2563aa707210"
 IntervalRootFinding = "d2bf35a9-74e0-55ec-b149-d360ff49b807"
 SymPy = "24249f21-da20-56a4-8eb1-6a02cf4ae2e6"
 SymPyPythonCall = "bc8888f7-b21e-4b7c-a06a-5d9c9496438c"
+Unitful = "1986cc42-f94f-5a68-af5c-568840ba703d"
 
 [extensions]
 RootsChainRulesCoreExt = "ChainRulesCore"
 RootsForwardDiffExt = "ForwardDiff"
 RootsIntervalRootFindingExt = "IntervalRootFinding"
 RootsSymPyExt = "SymPy"
 RootsSymPyPythonCallExt = "SymPyPythonCall"
+RootsUnitfulExt = "Unitful"
 
 [compat]
 Accessors = "0.1.33"

ext/RootsUnitfulExt.jl

@@ -0,0 +1,10 @@
+module RootsUnitfulExt
+using Unitful
+using Roots
+
+function Roots.find_zero_default_method(x0::Tuple{<:Quantity,<:Quantity})
+    T = eltype(ustrip.(float.(Roots._extrema(x0))))
+    T <: Union{Float16,Float32,Float64} ? Roots.Bisection() : Roots.A42()
+end
+
+end # module

test/test_extensions.jl

@@ -70,6 +70,13 @@ using ForwardDiff
     end
 end
 
+using Unitful
+@testset "Unitful" begin
+    f = x -> -exp(ustrip(x)) + 3
+    @test find_zero(f, (0u"nm", Inf * 1u"nm")) ≈
+          find_zero(x -> f(x * 1u"nm"), (0, Inf)) * 1u"nm"
+end
+
 #=
 using IntervalRootFinding
 @testset "IntervalRootFinding" begin