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Ensure internal ITP bounds are in proper order #1162

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Merged
ChrisRackauckas merged 2 commits into from
May 30, 2025
Merged

Ensure internal ITP bounds are in proper order #1162

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b243184
Ensure internal ITP bounds are in proper order
May 30, 2025
be30788
Test internal rootfinder on trickier problem
May 30, 2025
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6 changes: 3 additions & 3 deletions src/internal_itp.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -30,7 +30,7 @@ function SciMLBase.solve(prob::IntervalNonlinearProblem{IP, Tuple{T, T}}, alg::I
args...;
maxiters = 1000, kwargs...) where {IP, T}
f = Base.Fix2(prob.f, prob.p)
left, right = prob.tspan # a and b
left, right = minmax(prob.tspan...) # a and b
fl, fr = f(left), f(right)
ϵ = eps(T)
if iszero(fl)
Expand All @@ -40,7 +40,7 @@ function SciMLBase.solve(prob::IntervalNonlinearProblem{IP, Tuple{T, T}}, alg::I
return SciMLBase.build_solution(prob, alg, right, fr;
retcode = ReturnCode.ExactSolutionRight, left, right)
end
span = abs(right - left)
span = right - left
k1 = T(alg.scaled_k1) / span
n0 = T(alg.n0)
n_h = exponent(span / (2 * ϵ))
Expand All @@ -49,7 +49,7 @@ function SciMLBase.solve(prob::IntervalNonlinearProblem{IP, Tuple{T, T}}, alg::I

i = 1
while i ≤ maxiters
span = abs(right - left)
span = right - left
mid = (left + right) / 2
r = ϵ_s - (span / 2)

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10 changes: 10 additions & 0 deletions test/internal_rootfinder.jl
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Expand Up @@ -36,4 +36,14 @@ for Rootfinder in (InternalITP,)
@test abs.(solve(inp3, rf).u) ≈ sqrt.(p)
@test abs.(solve(inp4, rf).u) ≈ sqrt.(p)
end

# https://github.com/SciML/DifferentialEquations.jl/issues/1087
# Test with normal and reversed tspan.
# The expected zero is -acos(p), but there is another zero at acos(p) just outside tspan
f(u, p) = cos(u) - p
p = 0.9
inp1 = IntervalNonlinearProblem(f, (-1.1 * acos(p), 0.9 * acos(p)), p)
inp2 = IntervalNonlinearProblem(f, (0.9 * acos(p), -1.1 * acos(p)), p)
@test solve(inp1, rf).u ≈ -acos(p)
@test solve(inp2, rf).u ≈ -acos(p)
end
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