Parameter values can be supplied in the initial condition vector

[TorkelE]

MWE:

using ModelingToolkit, OrdinaryDiffEq, Plots

@variables t X(t)
@parameters p d
D = Differential(t)
eqs = [
    D(X) ~ p - d*X
]
@mtkbuild osys = ODESystem(eqs, t)

u0 = [X => 5.0, d => 0.2]
tspan = (0.0, 10.)
ps = [p => 5.0]
oprob = ODEProblem(osys, u0, tspan, ps)
sol = solve(oprob, Tsit5())
plot(sol)

If I then change d, this does have an effect on the result?

u0 = [X => 5.0, d => 0.5]
tspan = (0.0, 10.)
ps = [p => 5.0]
oprob = ODEProblem(osys, u0, tspan, ps)
sol = solve(oprob, Tsit5())
plot(sol)

[vyudu]

Does this need to be fixed? Seems like there's some discussion in #2743 about changing it being too breaking?

[ChrisRackauckas]

Let's discuss in the Monday chat if this should go into the v10. It would be breaking, yes, but I think it's a good correctness check to add. Either that or we just make the u0 be "all defaults", rather than forcing a split. But I think we should do something for the v10 because this is less than ideal.