FMU without state variables

[AnHeuermann]

Description

I have a (2.0, ME) FMU that doesn't have any state variables. It seems that FMI.jl is not catching these and calls the ODE solver on an empty array of states which results in a crash.

How to reproduce

mwe.mo

model Mwe
  Real x;
  Real y;
equation
  1 = x^2 + y*time;
  0 = x + y^2;
end Mwe;

Create 2.0 ModelExchange FMU with e.g. OpenModelica.
Windows FMU (remove the .zip part): Mwe.fmu.zip
Ubuntu Focal FMU: Mwe.fmu.zip

julia> using FMI
julia> myFMU = fmiLoad("Mwe.fmu");
julia> simData = fmiSimulate(myFMU, 0.0, 1.0; recordValues=["x", "y"])
ERROR: BoundsError: attempt to access 0-element Vector{Float64} at index [1]
Stacktrace:
  [1] getindex
    @ ./array.jl:861 [inlined]
  [2] ODE_DEFAULT_NORM
    @ ~/.julia/packages/DiffEqBase/Da1WO/src/common_defaults.jl:25 [inlined]
  [3] __init(prob::SciMLBase.ODEProblem{Vector{Float64}, Tuple{Float64, Float64}, true, Vector{Any}, SciMLBase.ODEFunction{true, FMI.var"#84#93"{FMU2Component}, LinearAlgebra.UniformScaling{Bool}, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED), Nothing}, Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}}, SciMLBase.StandardODEProblem}, alg::OrdinaryDiffEq.CompositeAlgorithm{Tuple{OrdinaryDiffEq.Vern7, OrdinaryDiffEq.Rodas4{0, false, LinearSolve.GenericLUFactorization{LinearAlgebra.RowMaximum}, typeof(OrdinaryDiffEq.DEFAULT_PRECS), Val{:forward}, true, nothing}}, OrdinaryDiffEq.AutoSwitch{OrdinaryDiffEq.Vern7, OrdinaryDiffEq.Rodas4{0, false, Nothing, typeof(OrdinaryDiffEq.DEFAULT_PRECS), Val{:forward}, true, nothing}, Rational{Int64}, Int64}}, timeseries_init::Tuple{}, ts_init::Tuple{}, ks_init::Tuple{}, recompile::Type{Val{true}}; saveat::Tuple{}, tstops::Tuple{}, d_discontinuities::Tuple{}, save_idxs::Nothing, save_everystep::Bool, save_on::Bool, save_start::Bool, save_end::Nothing, callback::SciMLBase.CallbackSet{Tuple{}, Tuple{SciMLBase.DiscreteCallback{DiffEqCallbacks.var"#27#28", DiffEqCallbacks.FunctionCallingAffect{FMI.var"#89#98"{Vector{UInt32}, Nothing, FMU2Component, FMICore.FMU2Solution}, DataStructures.BinaryMinHeap{Float64}, Vector{Float64}}, typeof(DiffEqCallbacks.functioncalling_initialize), typeof(SciMLBase.FINALIZE_DEFAULT)}, SciMLBase.DiscreteCallback{DiffEqCallbacks.var"#30#31", DiffEqCallbacks.SavingAffect{FMI.var"#91#100"{Vector{UInt32}, Vector{UInt32}, Nothing, FMU2Component}, Float64, Tuple{Float64, Float64}, DataStructures.BinaryMinHeap{Float64}, Vector{Float64}}, typeof(DiffEqCallbacks.saving_initialize), typeof(SciMLBase.FINALIZE_DEFAULT)}}}, dense::Bool, calck::Bool, dt::Float64, dtmin::Nothing, dtmax::Float64, force_dtmin::Bool, adaptive::Bool, gamma::Rational{Int64}, abstol::Nothing, reltol::Float64, qmin::Rational{Int64}, qmax::Int64, qsteady_min::Int64, qsteady_max::Int64, beta1::Nothing, beta2::Nothing, qoldinit::Rational{Int64}, controller::Nothing, fullnormalize::Bool, failfactor::Int64, maxiters::Int64, internalnorm::typeof(DiffEqBase.ODE_DEFAULT_NORM), internalopnorm::typeof(LinearAlgebra.opnorm), isoutofdomain::typeof(DiffEqBase.ODE_DEFAULT_ISOUTOFDOMAIN), unstable_check::typeof(DiffEqBase.ODE_DEFAULT_UNSTABLE_CHECK), verbose::Bool, timeseries_errors::Bool, dense_errors::Bool, advance_to_tstop::Bool, stop_at_next_tstop::Bool, initialize_save::Bool, progress::Bool, progress_steps::Int64, progress_name::String, progress_message::typeof(DiffEqBase.ODE_DEFAULT_PROG_MESSAGE), userdata::Nothing, allow_extrapolation::Bool, initialize_integrator::Bool, alias_u0::Bool, alias_du0::Bool, initializealg::OrdinaryDiffEq.DefaultInit, kwargs::Base.Pairs{Symbol, Bool, Tuple{Symbol, Symbol}, NamedTuple{(:default_set, :second_time), Tuple{Bool, Bool}}})
    @ OrdinaryDiffEq ~/.julia/packages/OrdinaryDiffEq/5B7d7/src/solve.jl:274
  [4] #__solve#502
    @ ~/.julia/packages/OrdinaryDiffEq/5B7d7/src/solve.jl:4 [inlined]
  [5] __solve(::SciMLBase.ODEProblem{Vector{Float64}, Tuple{Float64, Float64}, true, Vector{Any}, SciMLBase.ODEFunction{true, FMI.var"#84#93"{FMU2Component}, LinearAlgebra.UniformScaling{Bool}, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED), Nothing}, Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}}, SciMLBase.StandardODEProblem}, ::Nothing; default_set::Bool, kwargs::Base.Pairs{Symbol, Any, NTuple{4, Symbol}, NamedTuple{(:second_time, :callback, :dtmax, :reltol), Tuple{Bool, SciMLBase.CallbackSet{Tuple{}, Tuple{SciMLBase.DiscreteCallback{DiffEqCallbacks.var"#27#28", DiffEqCallbacks.FunctionCallingAffect{FMI.var"#89#98"{Vector{UInt32}, Nothing, FMU2Component, FMICore.FMU2Solution}, DataStructures.BinaryMinHeap{Float64}, Vector{Float64}}, typeof(DiffEqCallbacks.functioncalling_initialize), typeof(SciMLBase.FINALIZE_DEFAULT)}, SciMLBase.DiscreteCallback{DiffEqCallbacks.var"#30#31", DiffEqCallbacks.SavingAffect{FMI.var"#91#100"{Vector{UInt32}, Vector{UInt32}, Nothing, FMU2Component}, Float64, Tuple{Float64, Float64}, DataStructures.BinaryMinHeap{Float64}, Vector{Float64}}, typeof(DiffEqCallbacks.saving_initialize), typeof(SciMLBase.FINALIZE_DEFAULT)}}}, Float64, Float64}}})
    @ DifferentialEquations ~/.julia/packages/DifferentialEquations/TZ7Qg/src/default_solve.jl:9
  [6] #__solve#52
    @ ~/.julia/packages/DiffEqBase/Da1WO/src/solve.jl:1036 [inlined]
  [7] #solve_call#28
    @ ~/.julia/packages/DiffEqBase/Da1WO/src/solve.jl:448 [inlined]
  [8] solve_up(::SciMLBase.ODEProblem{Vector{Float64}, Tuple{Float64, Float64}, true, Vector{Any}, SciMLBase.ODEFunction{true, FMI.var"#84#93"{FMU2Component}, LinearAlgebra.UniformScaling{Bool}, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED), Nothing}, Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}}, SciMLBase.StandardODEProblem}, ::Nothing, ::Vector{Float64}, ::Vector{Any}; kwargs::Base.Pairs{Symbol, Any, Tuple{Symbol, Symbol, Symbol}, NamedTuple{(:callback, :dtmax, :reltol), Tuple{SciMLBase.CallbackSet{Tuple{}, Tuple{SciMLBase.DiscreteCallback{DiffEqCallbacks.var"#27#28", DiffEqCallbacks.FunctionCallingAffect{FMI.var"#89#98"{Vector{UInt32}, Nothing, FMU2Component, FMICore.FMU2Solution}, DataStructures.BinaryMinHeap{Float64}, Vector{Float64}}, typeof(DiffEqCallbacks.functioncalling_initialize), typeof(SciMLBase.FINALIZE_DEFAULT)}, SciMLBase.DiscreteCallback{DiffEqCallbacks.var"#30#31", DiffEqCallbacks.SavingAffect{FMI.var"#91#100"{Vector{UInt32}, Vector{UInt32}, Nothing, FMU2Component}, Float64, Tuple{Float64, Float64}, DataStructures.BinaryMinHeap{Float64}, Vector{Float64}}, typeof(DiffEqCallbacks.saving_initialize), typeof(SciMLBase.FINALIZE_DEFAULT)}}}, Float64, Float64}}})
    @ DiffEqBase ~/.julia/packages/DiffEqBase/Da1WO/src/solve.jl:805
  [9] #solve#33
    @ ~/.julia/packages/DiffEqBase/Da1WO/src/solve.jl:771 [inlined]
 [10] fmi2SimulateME(fmu::FMU2, c::Nothing, t_start::Float64, t_stop::Float64; tolerance::Nothing, dt::Nothing, solver::Nothing, customFx::Nothing, recordValues::Vector{String}, saveat::Nothing, x0::Nothing, setup::Nothing, reset::Nothing, instantiate::Nothing, freeInstance::Nothing, terminate::Nothing, inputValueReferences::Nothing, inputFunction::Nothing, parameters::Nothing, dtmax::Nothing, callbacks::Vector{Any}, showProgress::Bool, kwargs::Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
    @ FMI ~/.julia/packages/FMI/1vhoW/src/FMI2_sim.jl:814
 [11] #fmi2Simulate#107
    @ ~/.julia/packages/FMI/1vhoW/src/FMI2_sim.jl:1034 [inlined]
 [12] #fmi2Simulate#15
    @ ~/.julia/packages/FMI/1vhoW/src/FMI2_comp_wraps.jl:17 [inlined]
 [13] fmiSimulate(::FMU2, ::Float64, ::Vararg{Float64}; kwargs::Base.Pairs{Symbol, Vector{String}, Tuple{Symbol}, NamedTuple{(:recordValues,), Tuple{Vector{String}}}})
    @ FMI ~/.julia/packages/FMI/1vhoW/src/FMI.jl:527
 [14] top-level scope
    @ REPL[17]:1

Versions

• Julia Version 1.7.2
  Commit bf53498635 (2022-02-06 15:21 UTC)
  Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: Intel(R) Xeon(R) Gold 6248R CPU @ 3.00GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-12.0.1 (ORCJIT, cascadelake)
• FMI.jl: 0.9.0

[ThummeTo]

Didn't know that this is even possible :-D
In this case we should use a custom "simulation" loop without ODE-solver I guess?
So basically a loop over time that only sets FMU inputs and retrieves values of interest?
Best regards!

[ThummeTo]

This is not as trivial as I thought, because events must be handled correctly. Because we have no ODE, we can't use a ODE-solver and therefore we can't use the callbacks from DiffEqCallbacks.jl for event handling...

[JoKircher]

Will have a look