Unexpected UndefVarError

[dodoplus]

check:

using ModelingToolkit, OrdinaryDiffEq

@variables t

@connector function Pin(; name)
    sts = @variables begin
        v(t)                    # Potential at the pin [V]
        i(t), [connect = Flow]    # Current flowing into the pin [A]
    end
    ODESystem(Equation[], t, sts, [], name = name, defaults = Dict(v => 1.0, i => 1.0))
end

function Ground(; name)
    @named g = Pin()
    eqs = [g.v ~ 0]
    ODESystem(eqs, t, [], []; systems = [g], name = name)
end

function OnePort(; name, v_start = 0.0, i_start = 0.0)
    @named p = Pin()
    @named n = Pin()
    sts = @variables begin
        v(t) = v_start
        i(t) = i_start
    end
    eqs = [v ~ p.v - n.v
           0 ~ p.i + n.i
           i ~ p.i]
    return compose(ODESystem(eqs, t, sts, []; name = name), p, n)
end

function Resistor(; name, R)
    @named oneport = OnePort()
    @unpack v, i = oneport
    pars = @parameters R = R
    eqs = [
        v ~ i * R,
    ]
    extend(ODESystem(eqs, t, [], pars; name = name), oneport)
end

function ConstantVoltage(;name, V = 1.0)
    @named oneport = OnePort()
    @unpack v = oneport
    ps = @parameters V=V
    eqs = [
           V ~ v
          ]
    extend(ODESystem(eqs, t, [], ps; name=name), oneport)
end

function ECapacitor(;name, Q_start = 0.0)
    @named oneport = OnePort()
    @unpack v, i = oneport
    sts = @variables begin
        Q(t) = Q_start
    end
    D = Differential(t)
    eqs = [
           D(Q) ~ i
           v*Q ~ 1
          ]
    extend(ODESystem(eqs, t, sts, []; name=name), oneport)
end

@named source = ConstantVoltage(V=0.1)
@named ec = ECapacitor()
@named r = Resistor(R=1)
@named ground = Ground()

eqs = [
    connect(source.p, r.p)
    connect(r.p, ec.p)
    connect(ec.n, source.n , ground.g)
]

@named model = ODESystem(eqs, t, systems=[r, ec, source , ground])
sys = structural_simplify(model)
prob = ODAEProblem(sys, [], (0, 10.0))
sol = solve(prob, Rosenbrock23())
# retcode: Success
# Interpolation: 1st order linear
# t: 2-element Vector{Float64}:
#   0.0
#  10.0
# u: 2-element Vector{Vector{Float64}}:
#  []
#  []

Now, attempting to access r.i:

sol[r.i]

UndefVarError: ec₊Q(t) not defined

Stacktrace:
  [1] macro expansion
    @ ~/.julia/packages/ModelingToolkit/wAABB/src/structural_transformation/codegen.jl:206 [inlined]
  [2] macro expansion
    @ ~/.julia/packages/SymbolicUtils/qulQp/src/code.jl:351 [inlined]
  [3] macro expansion
    @ ~/.julia/packages/RuntimeGeneratedFunctions/6v5Gn/src/RuntimeGeneratedFunctions.jl:137 [inlined]
  [4] macro expansion
    @ ./none:0 [inlined]
  [5] generated_callfunc
    @ ./none:0 [inlined]
  [6] (::RuntimeGeneratedFunctions.RuntimeGeneratedFunction{(Symbol("##arg#8441539597060760774"), Symbol("##arg#2454277144290286779"), :t), ModelingToolkit.StructuralTransformations.var"#_RGF_ModTag", ModelingToolkit.StructuralTransformations.var"#_RGF_ModTag", (0xc04349c9, 0x620b07f0, 0x344f553c, 0x577f8862, 0x7170b4f0)})(::Vector{Float64}, ::Vector{Float64}, ::Float64)
    @ RuntimeGeneratedFunctions ~/.julia/packages/RuntimeGeneratedFunctions/6v5Gn/src/RuntimeGeneratedFunctions.jl:124
  [7] (::ModelingToolkit.StructuralTransformations.var"#generated_observed#244"{Bool, ModelingToolkit.BipartiteGraphs.Matching{ModelingToolkit.BipartiteGraphs.Unassigned, Vector{Union{ModelingToolkit.BipartiteGraphs.Unassigned, Int64}}}, TearingState{ODESystem}, Dict{Any, Any}, BitVector, Vector{SymbolicUtils.Code.Assignment}, Tuple{Vector{Vector{Int64}}, Vector{BitSet}}, SymbolicUtils.Code.NameState, Dict{Any, Int64}})(::Num, ::Vector{Float64}, ::Vararg{Any})
    @ ModelingToolkit.StructuralTransformations ~/.julia/packages/ModelingToolkit/wAABB/src/structural_transformation/codegen.jl:342
  [8] _broadcast_getindex_evalf
    @ ./broadcast.jl:670 [inlined]
  [9] _broadcast_getindex
    @ ./broadcast.jl:643 [inlined]
 [10] getindex
    @ ./broadcast.jl:597 [inlined]
 [11] copy
    @ ./broadcast.jl:899 [inlined]
 [12] materialize
    @ ./broadcast.jl:860 [inlined]
 [13] observed(A::ODESolution{Float64, 2, Vector{Vector{Float64}}, Nothing, Nothing, Vector{Float64}, Nothing, ODEProblem{Nothing, Tuple{Float64, Float64}, true, Vector{Float64}, ODEFunction{true, SciMLBase.AutoSpecialize, RuntimeGeneratedFunctions.RuntimeGeneratedFunction{(Symbol("##out#329"), Symbol("##arg#8441539597060760774"), Symbol("##arg#2454277144290286779"), :t), ModelingToolkit.StructuralTransformations.var"#_RGF_ModTag", ModelingToolkit.StructuralTransformations.var"#_RGF_ModTag", (0x77b8abe5, 0x2736dc4f, 0x6d0f9600, 0x632363cf, 0xfb62e9b0)}, LinearAlgebra.UniformScaling{Bool}, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, SparseArrays.SparseMatrixCSC{Bool, Int64}, Nothing, Nothing, Nothing, Vector{Symbol}, Symbol, Vector{Symbol}, ModelingToolkit.StructuralTransformations.var"#generated_observed#244"{Bool, ModelingToolkit.BipartiteGraphs.Matching{ModelingToolkit.BipartiteGraphs.Unassigned, Vector{Union{ModelingToolkit.BipartiteGraphs.Unassigned, Int64}}}, TearingState{ODESystem}, Dict{Any, Any}, BitVector, Vector{SymbolicUtils.Code.Assignment}, Tuple{Vector{Vector{Int64}}, Vector{BitSet}}, SymbolicUtils.Code.NameState, Dict{Any, Int64}}, Nothing, ODESystem}, Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}}, SciMLBase.StandardODEProblem}, Nothing, SciMLBase.LinearInterpolation{Vector{Float64}, Vector{Vector{Float64}}}, Nothing, Nothing}, sym::Num, i::Colon)
    @ SciMLBase ~/.julia/packages/SciMLBase/VKnrY/src/solutions/solution_interface.jl:132
 [14] getindex(A::ODESolution{Float64, 2, Vector{Vector{Float64}}, Nothing, Nothing, Vector{Float64}, Nothing, ODEProblem{Nothing, Tuple{Float64, Float64}, true, Vector{Float64}, ODEFunction{true, SciMLBase.AutoSpecialize, RuntimeGeneratedFunctions.RuntimeGeneratedFunction{(Symbol("##out#329"), Symbol("##arg#8441539597060760774"), Symbol("##arg#2454277144290286779"), :t), ModelingToolkit.StructuralTransformations.var"#_RGF_ModTag", ModelingToolkit.StructuralTransformations.var"#_RGF_ModTag", (0x77b8abe5, 0x2736dc4f, 0x6d0f9600, 0x632363cf, 0xfb62e9b0)}, LinearAlgebra.UniformScaling{Bool}, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, SparseArrays.SparseMatrixCSC{Bool, Int64}, Nothing, Nothing, Nothing, Vector{Symbol}, Symbol, Vector{Symbol}, ModelingToolkit.StructuralTransformations.var"#generated_observed#244"{Bool, ModelingToolkit.BipartiteGraphs.Matching{ModelingToolkit.BipartiteGraphs.Unassigned, Vector{Union{ModelingToolkit.BipartiteGraphs.Unassigned, Int64}}}, TearingState{ODESystem}, Dict{Any, Any}, BitVector, Vector{SymbolicUtils.Code.Assignment}, Tuple{Vector{Vector{Int64}}, Vector{BitSet}}, SymbolicUtils.Code.NameState, Dict{Any, Int64}}, Nothing, ODESystem}, Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}}, SciMLBase.StandardODEProblem}, Nothing, SciMLBase.LinearInterpolation{Vector{Float64}, Vector{Vector{Float64}}}, Nothing, Nothing}, sym::Num)
    @ SciMLBase ~/.julia/packages/SciMLBase/VKnrY/src/solutions/solution_interface.jl:88
 [15] top-level scope
    @ In[3]:1
 [16] eval
    @ ./boot.jl:368 [inlined]
 [17] include_string(mapexpr::typeof(REPL.softscope), mod::Module, code::String, filename::String)
    @ Base ./loading.jl:1428

[dodoplus]

PS:

The code is buggy:

    connect(source.p, r.p)
    connect(r.p, ec.p)  # <-should be r.n

However, the UndefVarError is still unexpected

[ChrisRackauckas]

Expansions were made lazy, this was fixed awhile back.