Parameters (and probably variables) occurring in events only are not inferred into ODESystems

[TorkelE]

If you have parameters which only occur in an event, these are not inferred as parameters of the system (in the same way as e.g. parameters of equations).

E.g. in this MWE, the parameter thres is not found in either system (to which it belong).

using ModelingToolkit

@variables t X(t)
@parameters p d
@parameters thres
D = Differential(t)
eq = D(X) ~ p - d*X

discrete_events = [(X > thres) => [X ~ X/2.0]]
@mtkbuild osys1 = ODESystem([eq], t; discrete_events)
parameters(osys1) # [p, d]

continuous_events = [(X ~ thres) => [X ~ X/2.0]]
@mtkbuild osys2 = ODESystem([eq], t; discrete_events)
parameters(osys2) # [p, d]

[SebastianM-C]

I think that's on purpose as parameters that appear in an event can be potentially modified during the callback. Are they present in the full_parameters(osys1)?

[TorkelE]

Yes, having these things be parameters (and not values) is useful because it means that they can be changed. However, since they are not added to the system, this is not possible (as you cannot interface with them through e.g. the integrator.

full_parameters(osys1)

also returns [p, d]