Indexing a residual of an InitializationProblem

Specific Domains Modelling & Simulations
1

I want to check the residual of the solution of an initializationproblem as done in this example: Initialization of ODESystems · ModelingToolkit.jl

However, my model is quite a bit more complex than the one in the example. So I would like to be able to index the residuals:

using ModelingToolkit, OrdinaryDiffEq
using ModelingToolkit: t_nounits as t, D_nounits as D

@parameters g
@variables x(t) y(t) [state_priority = 10] λ(t)
eqs = [D(D(x)) ~ λ * x
       D(D(y)) ~ λ * y - g
       x^2 + y^2 ~ 1]
@mtkbuild pend = ODESystem(eqs, t)

iprob = ModelingToolkit.InitializationProblem(pend, 0.0,
    [x => 1, y => 0.0, D(y) => 2.0, λ => 1], [g => 1], guesses = [λ => 1])
using NonlinearSolve
sol = solve(iprob)
sol.resid[x] # indexing the residual

But sol.resid[x] doesn’t work. Is this possible in any other way?

2

This should work, assuming the order of sol.resid is the same as the order of equations(sol.prob.f.sys)

for (u, e) in zip(sol.resid, equations(sol.prob.f.sys))
    println(u, "\t", e)
end
3

Yeah open an issue. This would be a good debugging tool, we just haven’t setup fancy indexing on this yet.

1 Like
4

Submitted an issue here: Indexing a residual of an InitializationProblem · Issue #3260 · SciML/ModelingToolkit.jl · GitHub