How to Create Global Parameters in ModelingToolkit.jl

Specific Domains Modelling & Simulations
4

Thanks for this tip. I gave GlobalScope() a try, and technically it works well, but I can see a duplication of the global parameter in parent components. For example, the following code produces comp with 2 parameters named rho

using ModelingToolkit

@variables t
@variables p(t)
@parameters rho
D = Differential(t)

rho = GlobalScope(rho)

fluid(;name) = ODESystem(Equation[], t, [p], [rho], defaults=[rho=>1000, p=>0], name=name)

@named A = fluid()
@named B = fluid()

eqs = [
    D(B.p) ~ A.p
    0 ~ (A.p) - (A.rho)
]

@named comp = ODESystem(eqs, t, [], [], systems=[A, B])

Here is the result for comp

julia> comp
Model comp with 2 equations
States (2):
  A₊p(t) [defaults to 0]
  B₊p(t) [defaults to 0]
Parameters (2):
  rho [defaults to 1000]
  rho [defaults to 1000]

The solution works well, if I run the model, it does seem to set rho globally

ps = [
    rho=>900
]
prob = ODEProblem(comp, [], (0,0.1), ps)
solve(prob, ImplicitEuler())

With result…

retcode: Success
Interpolation: 3rd order Hermite
t: 9-element Vector{Float64}:
 0.0
 1.0e-6
 1.2e-6
 3.2e-6
 2.3199999999999998e-5
 0.00022319999999999998
 0.0022231999999999994
 0.02222319999999999
 0.1
u: 9-element Vector{Vector{Float64}}:
 [900.0, 0.0]
 [900.0, 0.0009]
 [900.0, 0.00108]
 [900.0, 0.0028799999999999997]
 [900.0, 0.02088]
 [900.0, 0.20088]
 [900.0, 2.0008799999999995]
 [900.0, 20.00087999999999]
 [900.0, 90.0]