continuous_events fails to recognize vectors

[ufechner7]

The following example fails:

# Example two: Falling mass, attached to non-linear spring without compression stiffness,
# initially moving upwards with 4 m/s, using a callback to precisely calculate the discontinuities
using ModelingToolkit, OrdinaryDiffEq, LinearAlgebra

G_EARTH  = Float64[0.0, 0.0, -9.81]             # gravitational acceleration [m/s²]
L0::Float64 = -10.0                             # initial spring length      [m]
V0::Float64 = 4                                 # initial velocity           [m/s]

# model, Z component upwards
@parameters mass=1.0 c_spring0=50.0 damping=0.5 l0=L0
@variables t pos(t)[1:3] = [0.0, 0.0,  L0]
@variables   vel(t)[1:3] = [0.0, 0.0,  V0] 
@variables   acc(t)[1:3] = G_EARTH
@variables unit_vector(t)[1:3]  = [0.0, 0.0, -sign(L0)]
@variables c_spring(t) = c_spring0
@variables spring_force(t)[1:3] = [0.0, 0.0, 0.0]
@variables force(t) = 0.0 norm1(t) = abs(l0) spring_vel(t) = 0.0
D = Differential(t)

eqs = vcat(D.(pos)      ~ vel,
           D.(vel)      ~ acc,
           norm1        ~ norm(pos),
           unit_vector  ~ -pos/norm1,         # direction from point mass to origin
           spring_vel   ~ -unit_vector ⋅ vel,
           c_spring     ~ c_spring0 * (norm1 > abs(l0)),
           spring_force ~ (c_spring * (norm1 - abs(l0)) + damping * spring_vel) * unit_vector,
           acc          ~ G_EARTH + spring_force/mass)

@named sys = ODESystem(eqs, t; continuous_events = [norm(pos) ~ abs(L0)])
simple_sys = structural_simplify(sys)


duration = 10.0
dt = 0.02
tol = 1e-6
tspan = (0.0, duration)
ts    = 0:dt:duration
# initial state
u0 = Dict(pos=>[0,0,L0], vel=>[0,0,V0])

prob = ODEProblem(simple_sys, u0, tspan)
sol = solve(prob, Rodas5(), dt=dt, abstol=tol, reltol=tol, saveat=ts)
nothing

with the error message:

ERROR: LoadError: UndefVarError: `pos` not defined
Stacktrace:
  [1] macro expansion
    @ ~/.julia/packages/SymbolicUtils/ssQsQ/src/code.jl:418 [inlined]
  [2] macro expansion
    @ ~/.julia/packages/Symbolics/5BibL/src/build_function.jl:537 [inlined]
  [3] macro expansion
    @ ~/.julia/packages/SymbolicUtils/ssQsQ/src/code.jl:375 [inlined]
  [4] macro expansion
    @ ~/.julia/packages/RuntimeGeneratedFunctions/Yo8zx/src/RuntimeGeneratedFunctions.jl:163 [inlined]
  [5] macro expansion
    @ ./none:0 [inlined]
  [6] generated_callfunc(f::RuntimeGeneratedFunctions.RuntimeGeneratedFunction{…}, __args::Vararg{…}) where {…}
    @ ModelingToolkit ./none:0 [inlined]
  [7] (::RuntimeGeneratedFunctions.RuntimeGeneratedFunction{…})(::Vector{…}, ::Vector{…}, ::Vector{…}, ::Float64)
    @ RuntimeGeneratedFunctions ~/.julia/packages/RuntimeGeneratedFunctions/Yo8zx/src/RuntimeGeneratedFunctions.jl:150
  [8] #346
    @ ~/.julia/packages/ModelingToolkit/dCa81/src/systems/callbacks.jl:403 [inlined]
  [9] determine_event_occurance
    @ ~/.julia/packages/DiffEqBase/a6p43/src/callbacks.jl:290 [inlined]
 [10] find_callback_time(integrator::OrdinaryDiffEq.ODEIntegrator{…}, callback::ContinuousCallback{…}, counter::Int64)
    @ DiffEqBase ~/.julia/packages/DiffEqBase/a6p43/src/callbacks.jl:397
 [11] macro expansion
    @ ~/.julia/packages/DiffEqBase/a6p43/src/callbacks.jl:131 [inlined]
 [12] find_first_continuous_callback
    @ ~/.julia/packages/DiffEqBase/a6p43/src/callbacks.jl:126 [inlined]
 [13] find_first_continuous_callback
    @ ~/.julia/packages/DiffEqBase/a6p43/src/callbacks.jl:124 [inlined]
 [14] handle_callbacks!
    @ ~/.julia/packages/OrdinaryDiffEq/6qpRx/src/integrators/integrator_utils.jl:324 [inlined]
 [15] _loopfooter!(integrator::OrdinaryDiffEq.ODEIntegrator{…})
    @ OrdinaryDiffEq ~/.julia/packages/OrdinaryDiffEq/6qpRx/src/integrators/integrator_utils.jl:247
 [16] loopfooter!
    @ ~/.julia/packages/OrdinaryDiffEq/6qpRx/src/integrators/integrator_utils.jl:200 [inlined]
 [17] solve!(integrator::OrdinaryDiffEq.ODEIntegrator{…})
    @ OrdinaryDiffEq ~/.julia/packages/OrdinaryDiffEq/6qpRx/src/solve.jl:540
 [18] __solve(::ODEProblem{…}, ::Rodas5{…}; kwargs::@Kwargs{…})
    @ OrdinaryDiffEq ~/.julia/packages/OrdinaryDiffEq/6qpRx/src/solve.jl:6
 [19] __solve
    @ ~/.julia/packages/OrdinaryDiffEq/6qpRx/src/solve.jl:1 [inlined]
 [20] solve_call(_prob::ODEProblem{…}, args::Rodas5{…}; merge_callbacks::Bool, kwargshandle::Nothing, kwargs::@Kwargs{…})
    @ DiffEqBase ~/.julia/packages/DiffEqBase/a6p43/src/solve.jl:561
 [21] solve_call
    @ DiffEqBase ~/.julia/packages/DiffEqBase/a6p43/src/solve.jl:527 [inlined]
 [22] #solve_up#42
    @ DiffEqBase ~/.julia/packages/DiffEqBase/a6p43/src/solve.jl:1010 [inlined]
 [23] solve_up
    @ DiffEqBase ~/.julia/packages/DiffEqBase/a6p43/src/solve.jl:996 [inlined]
 [24] #solve#40
    @ DiffEqBase ~/.julia/packages/DiffEqBase/a6p43/src/solve.jl:933 [inlined]
 [25] top-level scope
    @ ~/repos/Tethers.jl/mwes/mwe02.jl:50
 [26] include(fname::String)
    @ Base.MainInclude ./client.jl:489
 [27] top-level scope
    @ REPL[1]:1
in expression starting at /home/ufechner/repos/Tethers.jl/mwes/mwe02.jl:50
Some type information was truncated. Use `show(err)` to see complete types.

even though pos(t) is defined as variable.

**Environment (please complete the following information):**

  - Output of `using Pkg; Pkg.status()`

```julia
Project Tethers v0.1.0
Status `~/repos/Tethers.jl/Project.toml`
  [992eb4ea] CondaPkg v0.2.22
  [16fef848] LiveServer v1.2.7
  [961ee093] ModelingToolkit v8.73.2
  [1dea7af3] OrdinaryDiffEq v6.62.0
  [9b87118b] PackageCompiler v2.1.15
  [438e738f] PyCall v1.96.3
  [d330b81b] PyPlot v2.11.2
  [21f18d07] Timers v0.1.5
  [44cfe95a] Pkg v1.10.0

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

Project Tethers v0.1.0
Status `~/repos/Tethers.jl/Manifest.toml`
  [47edcb42] ADTypes v0.2.5
⌅ [c3fe647b] AbstractAlgebra v0.33.0
  [1520ce14] AbstractTrees v0.4.4
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  [79e6a3ab] Adapt v3.7.2
  [ec485272] ArnoldiMethod v0.2.0
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  [00ebfdb7] CSTParser v3.3.6
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  [38540f10] CommonSolve v0.2.4
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⌅ [d5909c97] GroupsCore v0.4.2
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  [73f95e8e] LatticeRules v0.0.1
  [10f19ff3] LayoutPointers v0.1.15
  [50d2b5c4] Lazy v0.15.1
  [5078a376] LazyArrays v1.8.2
  [d3d80556] LineSearches v7.2.0
  [7ed4a6bd] LinearSolve v2.21.0
  [16fef848] LiveServer v1.2.7
  [2ab3a3ac] LogExpFunctions v0.3.26
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  [d8e11817] MLStyle v0.4.17
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  [d125e4d3] ManualMemory v0.1.8
  [a3b82374] MatrixFactorizations v2.1.0
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  [1dea7af3] OrdinaryDiffEq v6.62.0
  [90014a1f] PDMats v0.11.31
  [9b87118b] PackageCompiler v2.1.15
  [65ce6f38] PackageExtensionCompat v1.0.2
  [d96e819e] Parameters v0.12.3
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  [fa939f87] Pidfile v1.3.0
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  [f517fe37] Polyester v0.7.9
  [1d0040c9] PolyesterWeave v0.2.1
  [d236fae5] PreallocationTools v0.4.13
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  [21216c6a] Preferences v1.4.1
  [27ebfcd6] Primes v0.5.5
  [438e738f] PyCall v1.96.3
  [d330b81b] PyPlot v2.11.2
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⌅ [731186ca] RecursiveArrayTools v2.38.10
  [f2c3362d] RecursiveFactorization v0.2.21
  [189a3867] Reexport v1.2.2
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  [fdea26ae] SIMD v3.4.6
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  [476501e8] SLEEFPirates v0.6.42
⌅ [0bca4576] SciMLBase v2.10.0
  [e9a6253c] SciMLNLSolve v0.1.9
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⌅ [2efcf032] SymbolicIndexingInterface v0.2.2
⌅ [d1185830] SymbolicUtils v1.4.0
⌅ [0c5d862f] Symbolics v5.11.0
  [3783bdb8] TableTraits v1.0.1
  [bd369af6] Tables v1.11.1
  [1e6cf692] TestEnv v1.101.1
  [8290d209] ThreadingUtilities v0.5.2
  [a759f4b9] TimerOutputs v0.5.23
  [21f18d07] Timers v0.1.5
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  [3bb67fe8] TranscodingStreams v0.10.2
  [d5829a12] TriangularSolve v0.1.20
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  [3a884ed6] UnPack v1.0.2
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  [56f22d72] Artifacts
  [2a0f44e3] Base64
  [ade2ca70] Dates
  [8ba89e20] Distributed
  [f43a241f] Downloads v1.6.0
  [7b1f6079] FileWatching
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  [b77e0a4c] InteractiveUtils
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  [3fa0cd96] REPL
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Info Packages marked with ⌅ have new versions available but compatibility constraints restrict them from upgrading. To see why use `status --outdated -m`

• Output of versioninfo()

Julia Version 1.10.0-rc2
Commit dbb9c46795b (2023-12-03 15:25 UTC)
Build Info:
  Official https://julialang.org/ release
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: 16 × AMD Ryzen 7 7840U w/ Radeon  780M Graphics
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-15.0.7 (ORCJIT, znver3)
  Threads: 12 on 16 virtual cores

See also: https://github.com/ufechner7/Tethers.jl
This script https://github.com/ufechner7/Tethers.jl/blob/main/src/Tether_03b.jl works fine. Here I am using the lower level continues_events from DifferentialEquations.

[ufechner7]

If I use this line instead:

@named sys = ODESystem(eqs, t; continuous_events = [norm([pos[1],pos[2],pos[3]]) ~ abs(L0)])

it works, so it is really a problem related to using a symbolic vector variable.

[ChrisRackauckas]

Thanks for the MWE. Indeed it seems to be an issue with symbolic vectors.