ContinuousCallback not handled correctly

[sebapersson]

Describe the bug 🐞

This week I started to get errors in the SBMLImporter test-suite because ContinuousCallback if provided separately (not in the system) is not triggered correctly.

Expected behavior

Event handling should work as expected.

Minimal Reproducible Example 👇

using Catalyst, OrdinaryDiffEqRosenbrock

t = Catalyst.default_t()
model = @reaction_network begin
    k1 / C, S1 + S2 --> S3
    k2, S3 --> S1 + S2
end

u0 = [:S1 => 1.0, :S2 => 2.0, :S3 => 1.0]
ps = [:k1 => 0.75, :k2 => 0.25, :C => 1.0]
ode = ODEProblem(model, u0, (0.0, 2.0), ps)
sol1 = solve(ode, Rodas5P(), abstol = 1e-8, reltol = 1e-8)

function myaffect!(integrator)
    println("Activated")
    integrator[:S2] = 1 * integrator.ps[:C]
    return nothing
end
function mycond(u, t, integrator)
    return integrator[:S1] / integrator.ps[:C] - 0.75
end
cb = ContinuousCallback(mycond, myaffect!)
sol2 = solve(ode, Rodas4P(), callback = cb)

Error & Stacktrace ⚠️

Even though the condition in mycond function passes from positive to negative, the callback is not triggered.

Environment (please complete the following information):

• Output of using Pkg; Pkg.status()

  [479239e8] Catalyst v15.0.5
  [43230ef6] OrdinaryDiffEqRosenbrock v1.9.0

• Output of using Pkg; Pkg.status(; mode = PKGMODE_MANIFEST)

  [47edcb42] ADTypes v1.14.0
  [1520ce14] AbstractTrees v0.4.5
  [7d9f7c33] Accessors v0.1.42
  [79e6a3ab] Adapt v4.3.0
  [66dad0bd] AliasTables v1.1.3
  [ec485272] ArnoldiMethod v0.4.0
  [4fba245c] ArrayInterface v7.18.1
  [4c555306] ArrayLayouts v1.11.1
  [e2ed5e7c] Bijections v0.1.10
  [62783981] BitTwiddlingConvenienceFunctions v0.1.6
  [8e7c35d0] BlockArrays v1.6.3
  [70df07ce] BracketingNonlinearSolve v1.2.0
  [2a0fbf3d] CPUSummary v0.2.6
  [479239e8] Catalyst v15.0.5
  [d360d2e6] ChainRulesCore v1.25.1
  [fb6a15b2] CloseOpenIntervals v0.1.13
  [861a8166] Combinatorics v1.0.3
  [a80b9123] CommonMark v0.9.1
  [38540f10] CommonSolve v0.2.4
  [bbf7d656] CommonSubexpressions v0.3.1
  [f70d9fcc] CommonWorldInvalidations v1.0.0
  [34da2185] Compat v4.16.0
  [b152e2b5] CompositeTypes v0.1.4
  [a33af91c] CompositionsBase v0.1.2
  [2569d6c7] ConcreteStructs v0.2.3
  [187b0558] ConstructionBase v1.5.8
  [adafc99b] CpuId v0.3.1
  [a8cc5b0e] Crayons v4.1.1
  [9a962f9c] DataAPI v1.16.0
  [864edb3b] DataStructures v0.18.22
  [e2d170a0] DataValueInterfaces v1.0.0
  [2b5f629d] DiffEqBase v6.172.0
  [459566f4] DiffEqCallbacks v4.4.1
  [77a26b50] DiffEqNoiseProcess v5.24.1
  [163ba53b] DiffResults v1.1.0
  [b552c78f] DiffRules v1.15.1
  [a0c0ee7d] DifferentiationInterface v0.6.53
  [8d63f2c5] DispatchDoctor v0.4.19
  [31c24e10] Distributions v0.25.119
  [ffbed154] DocStringExtensions v0.9.4
  [5b8099bc] DomainSets v0.7.15
  [7c1d4256] DynamicPolynomials v0.6.1
  [06fc5a27] DynamicQuantities v1.8.0
  [4e289a0a] EnumX v1.0.5
  [f151be2c] EnzymeCore v0.8.8
  [e2ba6199] ExprTools v0.1.10
  [55351af7] ExproniconLite v0.10.14
  [7034ab61] FastBroadcast v0.3.5
  [9aa1b823] FastClosures v0.3.2
  [a4df4552] FastPower v1.1.2
  [1a297f60] FillArrays v1.13.0
  [64ca27bc] FindFirstFunctions v1.4.1
  [6a86dc24] FiniteDiff v2.27.0
  [1fa38f19] Format v1.3.7
⌅ [f6369f11] ForwardDiff v0.10.38
  [069b7b12] FunctionWrappers v1.1.3
  [77dc65aa] FunctionWrappersWrappers v0.1.3
  [d9f16b24] Functors v0.5.2
  [46192b85] GPUArraysCore v0.2.0
  [c27321d9] Glob v1.3.1
  [86223c79] Graphs v1.12.1
  [34004b35] HypergeometricFunctions v0.3.28
  [615f187c] IfElse v0.1.1
  [d25df0c9] Inflate v0.1.5
  [18e54dd8] IntegerMathUtils v0.1.2
  [8197267c] IntervalSets v0.7.11
  [3587e190] InverseFunctions v0.1.17
  [92d709cd] IrrationalConstants v0.2.4
  [82899510] IteratorInterfaceExtensions v1.0.0
  [692b3bcd] JLLWrappers v1.7.0
  [ae98c720] Jieko v0.2.1
  [98e50ef6] JuliaFormatter v2.1.2
⌅ [70703baa] JuliaSyntax v0.4.10
  [ccbc3e58] JumpProcesses v9.14.3
  [ba0b0d4f] Krylov v0.10.1
  [b964fa9f] LaTeXStrings v1.4.0
  [23fbe1c1] Latexify v0.16.7
  [10f19ff3] LayoutPointers v0.1.17
  [5078a376] LazyArrays v2.6.1
  [87fe0de2] LineSearch v0.1.4
  [d3d80556] LineSearches v7.3.0
  [7ed4a6bd] LinearSolve v3.11.0
  [2ab3a3ac] LogExpFunctions v0.3.29
  [d8e11817] MLStyle v0.4.17
  [1914dd2f] MacroTools v0.5.16
  [d125e4d3] ManualMemory v0.1.8
  [bb5d69b7] MaybeInplace v0.1.4
  [e1d29d7a] Missings v1.2.0
  [961ee093] ModelingToolkit v9.78.0
  [2e0e35c7] Moshi v0.3.5
  [46d2c3a1] MuladdMacro v0.2.4
  [102ac46a] MultivariatePolynomials v0.5.9
  [d8a4904e] MutableArithmetics v1.6.4
  [d41bc354] NLSolversBase v7.9.1
  [77ba4419] NaNMath v1.1.3
  [8913a72c] NonlinearSolve v4.8.0
  [be0214bd] NonlinearSolveBase v1.7.0
  [5959db7a] NonlinearSolveFirstOrder v1.5.0
  [9a2c21bd] NonlinearSolveQuasiNewton v1.4.0
  [26075421] NonlinearSolveSpectralMethods v1.2.0
  [6fe1bfb0] OffsetArrays v1.17.0
  [429524aa] Optim v1.12.0
  [bac558e1] OrderedCollections v1.8.0
  [bbf590c4] OrdinaryDiffEqCore v1.23.0
  [4302a76b] OrdinaryDiffEqDifferentiation v1.7.0
  [43230ef6] OrdinaryDiffEqRosenbrock v1.9.0
  [90014a1f] PDMats v0.11.35
  [d96e819e] Parameters v0.12.3
  [e409e4f3] PoissonRandom v0.4.4
  [f517fe37] Polyester v0.7.16
  [1d0040c9] PolyesterWeave v0.2.2
  [85a6dd25] PositiveFactorizations v0.2.4
⌅ [aea7be01] PrecompileTools v1.2.1
  [21216c6a] Preferences v1.4.3
  [08abe8d2] PrettyTables v2.4.0
  [27ebfcd6] Primes v0.5.7
  [43287f4e] PtrArrays v1.3.0
  [1fd47b50] QuadGK v2.11.2
  [74087812] Random123 v1.7.0
  [e6cf234a] RandomNumbers v1.6.0
  [3cdcf5f2] RecipesBase v1.3.4
  [731186ca] RecursiveArrayTools v3.33.0
  [189a3867] Reexport v1.2.2
  [ae029012] Requires v1.3.1
  [ae5879a3] ResettableStacks v1.1.1
  [79098fc4] Rmath v0.8.0
  [7e49a35a] RuntimeGeneratedFunctions v0.5.14
  [9dfe8606] SCCNonlinearSolve v1.2.0
  [94e857df] SIMDTypes v0.1.0
⌃ [0bca4576] SciMLBase v2.87.0
  [19f34311] SciMLJacobianOperators v0.1.4
⌅ [c0aeaf25] SciMLOperators v0.3.13
  [53ae85a6] SciMLStructures v1.7.0
  [efcf1570] Setfield v1.1.2
  [727e6d20] SimpleNonlinearSolve v2.4.0
  [699a6c99] SimpleTraits v0.9.4
  [ce78b400] SimpleUnPack v1.1.0
  [a2af1166] SortingAlgorithms v1.2.1
  [0a514795] SparseMatrixColorings v0.4.19
  [276daf66] SpecialFunctions v2.5.1
  [aedffcd0] Static v1.2.0
  [0d7ed370] StaticArrayInterface v1.8.0
  [90137ffa] StaticArrays v1.9.13
  [1e83bf80] StaticArraysCore v1.4.3
  [10745b16] Statistics v1.11.1
  [82ae8749] StatsAPI v1.7.0
  [2913bbd2] StatsBase v0.34.5
  [4c63d2b9] StatsFuns v1.5.0
  [7792a7ef] StrideArraysCore v0.5.7
  [892a3eda] StringManipulation v0.4.1
  [2efcf032] SymbolicIndexingInterface v0.3.40
  [19f23fe9] SymbolicLimits v0.2.2
  [d1185830] SymbolicUtils v3.27.0
  [0c5d862f] Symbolics v6.39.0
  [3783bdb8] TableTraits v1.0.1
  [bd369af6] Tables v1.12.0
  [ed4db957] TaskLocalValues v0.1.2
  [8ea1fca8] TermInterface v2.0.0
  [1c621080] TestItems v1.0.0
  [8290d209] ThreadingUtilities v0.5.3
  [a759f4b9] TimerOutputs v0.5.28
  [410a4b4d] Tricks v0.1.10
  [781d530d] TruncatedStacktraces v1.4.0
  [5c2747f8] URIs v1.5.2
  [3a884ed6] UnPack v1.0.2
  [1986cc42] Unitful v1.22.0
  [a7c27f48] Unityper v0.1.6
  [897b6980] WeakValueDicts v0.1.0
  [1d5cc7b8] IntelOpenMP_jll v2025.0.4+0
  [856f044c] MKL_jll v2025.0.1+1
  [efe28fd5] OpenSpecFun_jll v0.5.6+0
  [f50d1b31] Rmath_jll v0.5.1+0
  [1317d2d5] oneTBB_jll v2022.0.0+0
  [0dad84c5] ArgTools v1.1.2
  [56f22d72] Artifacts v1.11.0
  [2a0f44e3] Base64 v1.11.0
  [ade2ca70] Dates v1.11.0
  [8ba89e20] Distributed v1.11.0
  [f43a241f] Downloads v1.6.0
  [7b1f6079] FileWatching v1.11.0
  [9fa8497b] Future v1.11.0
  [b77e0a4c] InteractiveUtils v1.11.0
  [4af54fe1] LazyArtifacts v1.11.0
  [b27032c2] LibCURL v0.6.4
  [76f85450] LibGit2 v1.11.0
  [8f399da3] Libdl v1.11.0
  [37e2e46d] LinearAlgebra v1.11.0
  [56ddb016] Logging v1.11.0
  [d6f4376e] Markdown v1.11.0
  [a63ad114] Mmap v1.11.0
  [ca575930] NetworkOptions v1.2.0
  [44cfe95a] Pkg v1.11.0
  [de0858da] Printf v1.11.0
  [9a3f8284] Random v1.11.0
  [ea8e919c] SHA v0.7.0
  [9e88b42a] Serialization v1.11.0
  [1a1011a3] SharedArrays v1.11.0
  [6462fe0b] Sockets v1.11.0
  [2f01184e] SparseArrays v1.11.0
  [4607b0f0] SuiteSparse
  [fa267f1f] TOML v1.0.3
  [a4e569a6] Tar v1.10.0
  [8dfed614] Test v1.11.0
  [cf7118a7] UUIDs v1.11.0
  [4ec0a83e] Unicode v1.11.0
  [e66e0078] CompilerSupportLibraries_jll v1.1.1+0
  [deac9b47] LibCURL_jll v8.6.0+0
  [e37daf67] LibGit2_jll v1.7.2+0
  [29816b5a] LibSSH2_jll v1.11.0+1
  [c8ffd9c3] MbedTLS_jll v2.28.6+0
  [14a3606d] MozillaCACerts_jll v2023.12.12
  [4536629a] OpenBLAS_jll v0.3.27+1
  [05823500] OpenLibm_jll v0.8.5+0
  [bea87d4a] SuiteSparse_jll v7.7.0+0
  [83775a58] Zlib_jll v1.2.13+1
  [8e850b90] libblastrampoline_jll v5.11.0+0
  [8e850ede] nghttp2_jll v1.59.0+0
  [3f19e933] p7zip_jll v17.4.0+2

• Output of versioninfo()

Julia Version 1.11.5
Commit 760b2e5b739 (2025-04-14 06:53 UTC)
Build Info:
  Official https://julialang.org/ release
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: 14 × Intel(R) Core(TM) Ultra 7 165U
  WORD_SIZE: 64
  LLVM: libLLVM-16.0.6 (ORCJIT, alderlake)
Threads: 1 default, 0 interactive, 1 GC (on 14 virtual cores)
Environment:
  JULIA_EDITOR = code
  JULIA_NUM_THREADS = 

Additional context

I get the same error on Catalyst v15.0.4, so Catalyst is probably not the root-cause (might be MTK related). This was not causing any problems last Sunday (2025-03-05).

[TorkelE]

I've forwarded it as an MTK example, let's see if they know anything about it.
SciML/ModelingToolkit.jl#3621

[sebapersson]

Thanks for the fast reply!

[ChrisRackauckas]

Are you sure this MWE is exactly the code that regressed? Do you have a manifest where this exact code worked?

Because since day 1 of the DiffEq system it has been noted that mycond(u, t, integrator) has the property that u is properly interpolated while integrator is just the integrator, so you need to be careful to properly evaluate any value that comes from the integrator. In this case, integrator[:S1] / integrator.ps[:C] - 0.75 is just a constant because it's independent of t, and so it's impossible for that to trigger an event. You either need to use u[1] / integrator.ps[:C] - 0.75 or integrator(t)[1] / integrator.ps[:C] - 0.75 etc. So I would venture to guess that the code that is written above never triggered an event (it shouldn't've ever triggered an event and I'm not sure how it would), and that this MWE is a reduction from some other code that does not (or at least shouldn't) codegen to this form.

I would presume SBMLImporter is using the MTK symbolic event formulation? Do you have an MWE in the symbolic event form?

[sebapersson]

Thanks for the clarification, doing

function mycond(u, t, integrator)
    return u[1] / integrator.ps[:C] - 0.75
end

solves the problem (the problem was that I assumed the order of states). This brings a follow up; given that u[:S1] / integrator.ps[:C] - 0.75 does not work, is ModelingToolkit.getu the recommended way to get specie indices?

[ChrisRackauckas]

We highly recommend using MTK's symbolic event handling system since there are other considerations, particularly when DAEs are involved, that have to be worked through. This is all described here:

https://docs.sciml.ai/ModelingToolkit/stable/basics/Events/

For your case here, the condition is [S1/C - 0.75 ~ 0] and the affect! is just [S1 ~ 1 * C]. In MTK v10 that equation will be unchanged. But if you had for example [S1 ~ S1 + 1], then due to v10's SciML/ModelingToolkit.jl#3452, that changes to the discrete update equation [S1 ~ pre(S1) + 1] (which IMO is pretty clear on what it's disambiguating and why it's being changed).

You can use getu and other SII tools directly, and index the u for that as well. But if you start getting into DAEs then the implicit discrete callback system has other advantages in how it handles reinitialization, something that will be described in detail in a blog post about the v10 release. So for a basic ODE like this, sure it's just a syntax thing, but for the trickier DAE cases it does some pretty necessary things which is why we are trying to push people in that direction for any MTK usage. With ImperativeAffect using a symbolic condition and a general code for the affect, even that should be usable in the difficult cases and still have a symbolic condition, so "most" cases shouldn't need to call out to a fully manual callback. But if you do need to, I'd be curious to know more about what cases aren't covered here (generally the issue would be if you required non-pure functions in some odd way).

[isaacsas]

@ChrisRackauckas should functional affects then not be using integ.u as in https://docs.sciml.ai/ModelingToolkit/stable/basics/Events/#func_affects ?

[ChrisRackauckas]

affect! is different. This is just about the condition having a constant integrator argument.

[isaacsas]

Perhaps there should also be a functional condition at some point to allow for more flexibility there?

[ChrisRackauckas]

Yes maybe... I'd hope we can try to not due that though, since some of the tricks for improving the robustness of the detection can require knowing the event equations. Right now you can do the full fallback at this point. We can revisit it if people are hitting cases where this shows up, but at least all of the cases so far could/should hit the symbolic form.