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Fix FieldError for Magnus/Linear integrators with OrdinaryDiffEqDiffe… #3464

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Fix FieldError for Magnus/Linear integrators with OrdinaryDiffEqDiffe… #3464

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ff465b8
Fix FieldError for Magnus/Linear integrators with OrdinaryDiffEqDiffe…
Apr 17, 2026
8f47539
Use real Magnus integrators in regression test for #3232
Apr 17, 2026
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1 change: 1 addition & 0 deletions lib/OrdinaryDiffEqDifferentiation/src/OrdinaryDiffEqDifferentiation.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,7 @@ using OrdinaryDiffEqCore: OrdinaryDiffEqAlgorithm, OrdinaryDiffEqAdaptiveImplici
OrdinaryDiffEqImplicitAlgorithm, CompositeAlgorithm,
OrdinaryDiffEqExponentialAlgorithm,
OrdinaryDiffEqAdaptiveExponentialAlgorithm,
OrdinaryDiffEqLinearExponentialAlgorithm,
StochasticDiffEqNewtonAlgorithm, StochasticDiffEqNewtonAdaptiveAlgorithm,
StochasticDiffEqJumpNewtonAdaptiveAlgorithm,
StochasticDiffEqJumpNewtonDiffusionAdaptiveAlgorithm,
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8 changes: 8 additions & 0 deletions lib/OrdinaryDiffEqDifferentiation/src/alg_utils.jl
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Expand Up @@ -32,6 +32,12 @@ function _alg_autodiff(
) where {CS, AD, FDT, ST, CJ, Controller}
return Val{AD}()
end
# OrdinaryDiffEqLinearExponentialAlgorithm subtypes (Magnus integrators, LieEuler,
# CG methods, etc.) have NO autodiff field — their only fields are krylov, m, iop.
# They must be excluded before the generic ExponentialAlgorithm dispatch below.
function _alg_autodiff(::OrdinaryDiffEqLinearExponentialAlgorithm)
return Val{false}()
end
function _alg_autodiff(
alg::Union{
OrdinaryDiffEqExponentialAlgorithm{CS, AD},
Expand Down Expand Up @@ -66,6 +72,8 @@ Base.@pure function determine_chunksize(u, CS)
end
end



function DiffEqBase.prepare_alg(
alg::Union{
OrdinaryDiffEqAdaptiveImplicitAlgorithm{
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28 changes: 28 additions & 0 deletions lib/OrdinaryDiffEqDifferentiation/test/differentiation_traits_tests.jl
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Expand Up @@ -43,3 +43,31 @@ sol = solve(prob2, Rosenbrock23(autodiff = AutoForwardDiff(chunksize = 1)))

sol = solve(prob2, Rosenbrock23(autodiff = AutoFiniteDiff()))
@test ≈(good_sol[:, end], sol[:, end], rtol = 1.0e-2)

# Regression test for issue #3232:
# OrdinaryDiffEqLinearExponentialAlgorithm subtypes (MagnusGL6, etc.)
# have no `autodiff` field; _alg_autodiff and prepare_alg must not crash.
using OrdinaryDiffEqDifferentiation: _alg_autodiff
using OrdinaryDiffEqCore: OrdinaryDiffEqLinearExponentialAlgorithm
using DiffEqBase: prepare_alg

struct MockMagnusAlg <: OrdinaryDiffEqLinearExponentialAlgorithm
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krylov::Bool
m::Int
iop::Int
end

@testset "LinearExponentialAlgorithm autodiff traits (issue #3232)" begin
mock = MockMagnusAlg(false, 30, 0)

# _alg_autodiff must return Val{false}() instead of accessing alg.autodiff
@test _alg_autodiff(mock) == Val{false}()

# prepare_alg must return the algorithm unchanged (no AD preparation needed)
u0 = ones(2)
mock_prob = ODEProblem((du, u, p, t) -> du .= 0, u0, (0.0, 1.0))
@test prepare_alg(mock, u0, nothing, mock_prob) === mock

# forwarddiffs_model must return false
@test SciMLBase.forwarddiffs_model(mock) == false
end
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