Overridden default set on observed quantity not propagating to its alias

[yanshuchang]

using ModelingToolkit, Plots, DifferentialEquations

@variables t

@connector function Pin(;name)
    sts = @variables v(t)=1.0 i(t)=1.0 [connect = Flow]
    ODESystem(Equation[], t, sts, []; name=name)
end

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

function OnePort(;name)
    @named p = Pin()
    @named n = Pin()
    sts = @variables v(t)=1.0 i(t)=1.0
    eqs = [
           v ~ p.v - n.v
           0 ~ p.i + n.i
           i ~ p.i
          ]
    compose(ODESystem(eqs, t, sts, []; name=name), p, n)
end

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

function Capacitor(;name, C = 1.0)
    @named oneport = OnePort()
    @unpack v, i = oneport
    ps = @parameters C=C
    D = Differential(t)
    eqs = [
           D(v) ~ i / C
          ]
    extend(ODESystem(eqs, t, [], ps; 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 Inductor(;name, L = 1.0)
    @named oneport = OnePort()
    @unpack v, i = oneport
    pars = @parameters L = L
    D = Differential(t)

    eqs = [

       #D(v) ~ i / C
       D(i) ~ 1/L * v,
    ]
    extend(ODESystem(eqs, t, [], pars; name = name), oneport)
end


R = 1.0
C = 1.0
V = 20
L = 1.0


@named resistor   =  Resistor(R=R)
@named capacitor  =  Capacitor(C=C)
@named source     =  ConstantVoltage(V=V)
@named inductor   =  Inductor(L=L)
@named ground     =  Ground()

rc_eqs = [
    connect(source.p, inductor.p)
    connect(source.n, inductor.n)
    #connect(capacitor.n, source.n)
    connect(source.n, ground.g)
         ]

@named _rc_model = ODESystem(rc_eqs, t)
@named rc_model = compose(_rc_model,
                          [inductor, source, ground])
sys = structural_simplify(rc_model)
u0 = [
      inductor.v => -1
     ]
prob = ODAEProblem(sys, u0, (0, 10.0))
sol = solve(prob, Tsit5())
plot(sol)
plot(sol(0:0.1:10, idxs = inductor.i),label='A')
#plot(sol(inductor.v),label='A')
sol(0:0.1:10, idxs = inductor.v)

To put it simply, I connect the inductor and the 20V voltage source together, and then set the initial value of the inductor voltage to -1. It stands to reason that this situation does not exist and the program should report an error. Why does MTK still default the initial value of the voltage across the inductor to 20? Is this a bug of mtk?

[bowenszhu]

Could you please firstly read GitHub's guide on Creating and highlighting code blocks?
https://docs.github.com/en/get-started/writing-on-github/working-with-advanced-formatting/creating-and-highlighting-code-blocks

[yanshuchang]

@ bowenszhu Thank you, but I do not get your meaning. Did you mean that if there are any thing wrong with my code attached here? You can point it directly.

[ChrisRackauckas]

@AayushSabharwal was this handled?

[AayushSabharwal]

Not really. Setting the default for inductor.v doesn't work since it's an observed quantity, and if you trace the observed values:

• inductor.v ~ source.v
• source.v ~ source.V
inductor.v has a constant value, set by the parameter source.V

At best MTK should warn if default values contain an observed variable?

[ChrisRackauckas]

That should be handled in the initialize system then.