Non-existent variable missing from variable map

[baggepinnen]

On

(jl_uvAQbg) pkg> st
      Status `/tmp/jl_uvAQbg/Project.toml`
  [961ee093] ModelingToolkit v8.14.0

The following error makes no sense to me, there is no variable in this system named inertia2₊phiˍtt.

julia> prob = ODEProblem(sys, Pair[], (0.0, 1.0))
ERROR: ArgumentError: Term{Real, Base.ImmutableDict{DataType, Any}}[inertia2₊phiˍtt(t)] are missing from the variable map.
Stacktrace:
 [1] throw_missingvars(vars::Vector{Term{Real, Base.ImmutableDict{DataType, Any}}})
   @ ModelingToolkit ~/.julia/packages/ModelingToolkit/fp90z/src/variables.jl:100
 [2] _varmap_to_vars(varmap::Dict{Any, Any}, varlist::Vector{Term{Real, Base.ImmutableDict{DataType, Any}}}; defaults::Dict{Any, Any}, check::Bool, toterm::typeof(Symbolics.diff2term))
   @ ModelingToolkit ~/.julia/packages/ModelingToolkit/fp90z/src/variables.jl:94
 [3] varmap_to_vars(varmap::Vector{Pair}, varlist::Vector{Term{Real, Base.ImmutableDict{DataType, Any}}}; defaults::Dict{Any, Any}, check::Bool, toterm::Function, promotetoconcrete::Nothing, tofloat::Bool, use_union::Bool)
   @ ModelingToolkit ~/.julia/packages/ModelingToolkit/fp90z/src/variables.jl:63
 [4] process_DEProblem(constructor::Type, sys::ODESystem, u0map::Vector{Pair}, parammap::SciMLBase.NullParameters; implicit_dae::Bool, du0map::Nothing, version::Nothing, tgrad::Bool, jac::Bool, checkbounds::Bool, sparse::Bool, simplify::Bool, linenumbers::Bool, parallel::Symbolics.SerialForm, eval_expression::Bool, use_union::Bool, kwargs::Base.Pairs{Symbol, Bool, Tuple{Symbol, Symbol}, NamedTuple{(:has_difference, :check_length), Tuple{Bool, Bool}}})
   @ ModelingToolkit ~/.julia/packages/ModelingToolkit/fp90z/src/systems/diffeqs/abstractodesystem.jl:648
 [5] (ODEProblem{true})(sys::ODESystem, u0map::Vector{Pair}, tspan::Tuple{Float64, Float64}, parammap::SciMLBase.NullParameters; callback::Nothing, check_length::Bool, kwargs::Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
   @ ModelingToolkit ~/.julia/packages/ModelingToolkit/fp90z/src/systems/diffeqs/abstractodesystem.jl:744
 [6] (ODEProblem{true})(sys::ODESystem, u0map::Vector{Pair}, tspan::Tuple{Float64, Float64}, parammap::SciMLBase.NullParameters) (repeats 2 times)
   @ ModelingToolkit ~/.julia/packages/ModelingToolkit/fp90z/src/systems/diffeqs/abstractodesystem.jl:743
 [7] ODEProblem(::ODESystem, ::Vector{Pair}, ::Vararg{Any}; kwargs::Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
   @ ModelingToolkit ~/.julia/packages/ModelingToolkit/fp90z/src/systems/diffeqs/abstractodesystem.jl:720
 [8] ODEProblem(::ODESystem, ::Vector{Pair}, ::Vararg{Any})
   @ ModelingToolkit ~/.julia/packages/ModelingToolkit/fp90z/src/systems/diffeqs/abstractodesystem.jl:720
 [9] top-level scope
   @ REPL[41]:1

julia> inertia2
Model inertia2 with 5 (7) equations
States (7):
  phi(t) [defaults to 0.0]
  w(t) [defaults to 0.0]
  a(t) [defaults to 0.0]
  flange_a₊phi(t) [defaults to 0.0]
  flange_a₊tau(t) [defaults to 0.0]
  flange_b₊phi(t) [defaults to 0.0]
  flange_b₊tau(t) [defaults to 0.0]
Parameters (1):
  J [defaults to 1]

Can be reproduced by

using ModelingToolkit, OrdinaryDiffEq, Plots
using ModelingToolkitStandardLibrary.Mechanical.Rotational
using ModelingToolkitStandardLibrary.Blocks: t, Sine
using ModelingToolkit: connect

@named inertia1 = Inertia(; J = 1)
@named inertia2 = Inertia(; J = 1)
@named spring = Spring(; c = 1000)
@named damper = Damper(; d = 10)
@named torque = Torque()
@named u = Sine(frequency=30/2pi)

eqs = [
    connect(torque.flange, inertia1.flange_a)
    connect(inertia1.flange_b, spring.flange_a, damper.flange_a)
    connect(inertia2.flange_a, spring.flange_b, damper.flange_b)
    connect(torque.tau, u.output)
]

@named model = ODESystem(eqs, t; systems = [torque, inertia1, inertia2, spring, damper, u])

sys = structural_simplify(model)
prob = ODEProblem(sys, Pair[], (0.0, 1.0)) # This errors
sol = solve(prob, Rodas5())

[YingboMa]

Yeah, it's just saying it needs D(D(inertia2.phi)) to be initialized as well.

[baggepinnen]

Could we perhaps catch that this is the problem and indicate that D(D(inertia2.phi)) needs init? The current error message relies on the user knowing that D(D(inertia2.phi)) is lowered to phi_tt which at least I was not smart enough to figure out :P

[baggepinnen]

By the way, I don't see the reason why it would need the acceleration. This is a linear system that has a minimal realization with 4 states, two positions and two velocities, and I can simulate this providing only initial conditions for these 4 states.

[YingboMa]

It doesn't seem to introduce new derivatives anymore.