# ModelingToolkit 9.39 is broken, 9.40.1 works well
**URL:** https://discourse.julialang.org/t/modelingtoolkit-9-39-is-broken-9-40-1-works-well/119670
**Category:** Modelling & Simulations
**Tags:** package, modelingtoolkit
**Created:** [September 21, 2024, 10:32am UTC](https://discourse.julialang.org/t/modelingtoolkit-9-39-is-broken-9-40-1-works-well/119670 "2024-09-21T10:32:54Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [September 21, 2024, 10:32am UTC](https://discourse.julialang.org/t/modelingtoolkit-9-39-is-broken-9-40-1-works-well/119670/1 "2024-09-21T10:32:54Z")
Steps to reproduce:
```julia
git clone https://github.com/ufechner7/Tethers.jl/
cd Tethers.jl
git checkout broken
julia --project
```
and then in Julia
```julia
using Pkg
Pkg.update()
include("src/Tether_01.jl")
```
This gives the following stack trace:
```julia
ERROR: LoadError: MethodError: no method matching iterate(::Nothing)
Closest candidates are:
iterate(::Combinatorics.Combinations)
@ Combinatorics ~/.julia/packages/Combinatorics/Udg6X/src/combinations.jl:13
iterate(::Combinatorics.Combinations, ::Any)
@ Combinatorics ~/.julia/packages/Combinatorics/Udg6X/src/combinations.jl:13
iterate(::Combinatorics.CoolLexCombinations)
@ Combinatorics ~/.julia/packages/Combinatorics/Udg6X/src/combinations.jl:87
...
Stacktrace:
[1] isempty(itr::Nothing)
@ Base ./essentials.jl:957
[2] process_DEProblem(constructor::Type, sys::ODESystem, u0map::Nothing, parammap::SciMLBase.NullParameters; implicit_dae::Bool, du0map::Nothing, version::Nothing, tgrad::Bool, jac::Bool, checkbounds::Bool, sparse::Bool, simplify::Bool, linenumbers::Bool, parallel::Symbolics.SerialForm, eval_expression::Bool, eval_module::Module, use_union::Bool, tofloat::Bool, symbolic_u0::Bool, u0_constructor::typeof(identity), guesses::Dict{…}, t::Float64, warn_initialize_determined::Bool, build_initializeprob::Bool, initialization_eqs::Vector{…}, fully_determined::Bool, check_units::Bool, kwargs::@Kwargs{…})
@ ModelingToolkit ~/.julia/packages/ModelingToolkit/NWBfd/src/systems/diffeqs/abstractodesystem.jl:822
[3] process_DEProblem
@ ~/.julia/packages/ModelingToolkit/NWBfd/src/systems/diffeqs/abstractodesystem.jl:766 [inlined]
[4] (ODEProblem{…})(sys::ODESystem, u0map::Nothing, tspan::Tuple{…}, parammap::SciMLBase.NullParameters; callback::Nothing, check_length::Bool, warn_initialize_determined::Bool, eval_expression::Bool, eval_module::Module, kwargs::@Kwargs{})
@ ModelingToolkit ~/.julia/packages/ModelingToolkit/NWBfd/src/systems/diffeqs/abstractodesystem.jl:995
[5] ODEProblem
@ ~/.julia/packages/ModelingToolkit/NWBfd/src/systems/diffeqs/abstractodesystem.jl:983 [inlined]
[6] (ODEProblem{true, SciMLBase.AutoSpecialize})(sys::ODESystem, u0map::Nothing, tspan::Tuple{Float64, Float64})
@ ModelingToolkit ~/.julia/packages/ModelingToolkit/NWBfd/src/systems/diffeqs/abstractodesystem.jl:983
[7] (ODEProblem{true})(::ODESystem, ::Nothing, ::Vararg{Any}; kwargs::@Kwargs{})
@ ModelingToolkit ~/.julia/packages/ModelingToolkit/NWBfd/src/systems/diffeqs/abstractodesystem.jl:970
[8] (ODEProblem{true})(::ODESystem, ::Nothing, ::Vararg{Any})
@ ModelingToolkit ~/.julia/packages/ModelingToolkit/NWBfd/src/systems/diffeqs/abstractodesystem.jl:969
[9] ODEProblem(::ODESystem, ::Nothing, ::Vararg{Any}; kwargs::@Kwargs{})
@ ModelingToolkit ~/.julia/packages/ModelingToolkit/NWBfd/src/systems/diffeqs/abstractodesystem.jl:959
[10] ODEProblem(::ODESystem, ::Nothing, ::Vararg{Any})
@ ModelingToolkit ~/.julia/packages/ModelingToolkit/NWBfd/src/systems/diffeqs/abstractodesystem.jl:958
[11] top-level scope
@ ~/repos/Tethers.jl/src/Tether_01.jl:25
[12] include(fname::String)
@ Base.MainInclude ./client.jl:489
[13] top-level scope
@ REPL[4]:1
in expression starting at /home/ufechner/repos/Tethers.jl/src/Tether_01.jl:25
Some type information was truncated. Use `show(err)` to see complete types.
```
The error is reported for this line:
```julia
prob = ODEProblem(simple_sys, nothing, (0.0, duration))
```
All works fine with ModelingToolkit 9.38 or older. It also fails with ModelingToolkit 9.40. Shall I create a bugreport?
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [September 21, 2024, 12:06pm UTC](https://discourse.julialang.org/t/modelingtoolkit-9-39-is-broken-9-40-1-works-well/119670/2 "2024-09-21T12:06:59Z")
@cryptic.ax didn’t you just handle something about this?
---
### Author:  [@cryptic.ax](https://discourse.julialang.org/u/cryptic.ax)
#### Post date: [September 21, 2024, 12:13pm UTC](https://discourse.julialang.org/t/modelingtoolkit-9-39-is-broken-9-40-1-works-well/119670/3 "2024-09-21T12:13:00Z")
Yes, this looks like it should be fixed on MTK master
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [September 21, 2024, 12:40pm UTC](https://discourse.julialang.org/t/modelingtoolkit-9-39-is-broken-9-40-1-works-well/119670/4 "2024-09-21T12:40:38Z")
Oh I’ll release, sorry didn’t realized I missed that part.
---
### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [September 21, 2024, 1:39pm UTC](https://discourse.julialang.org/t/modelingtoolkit-9-39-is-broken-9-40-1-works-well/119670/5 "2024-09-21T13:39:59Z")
I updated the branch `broken` of the repo `Tethers.jl` to use MTK 9.40.1, and I can run the example now. But I get a warning that I did NOT get with the older MTK version:
```julia
julia> include("src/Tether_01.jl")
┌ Warning: Initialization system is overdetermined. 1 equations for 0 unknowns. Initialization will default to using least squares. To suppress this warning pass warn_initialize_determined = false. To make this warning into an error, pass fully_determined = true
└ @ ModelingToolkit ~/.julia/packages/ModelingToolkit/AS70O/src/systems/diffeqs/abstractodesystem.jl:1465
3.125912 seconds (4.50 M allocations: 295.207 MiB, 2.24% gc time, 99.99% compilation time)
OK
```
Any idea why?
My code:
```julia
# Example one: Falling mass.
using ModelingToolkit, OrdinaryDiffEq, ControlPlots
using ModelingToolkit: t_nounits as t, D_nounits as D
G_EARTH::Vector{Float64} = [0.0, 0.0, -9.81] # gravitational acceleration [m/s²]
# definiting the model
@variables pos(t)[1:3] = [0.0, 0.0, 0.0]
@variables vel(t)[1:3] = [0.0, 0.0, 50.0]
@variables acc(t)[1:3] = [0.0, 0.0, -9.81]
eqs = vcat(D(pos) ~ vel,
D(vel) ~ acc,
acc ~ G_EARTH)
@named sys = ODESystem(eqs, t)
simple_sys = structural_simplify(sys)
# running the simulation
duration = 10.0
dt = 0.02
tol = 1e-6
ts = 0:dt:duration
prob = ODEProblem(simple_sys, nothing, (0.0, duration))
@time sol = solve(prob, Rodas5(), dt=dt, abstol=tol, reltol=tol, saveat=ts)
# plotting the result
X = sol.t
POS_Z = stack(sol[pos], dims=1)[:,3]
VEL_Z = stack(sol[vel], dims=1)[:,3]
p = plot(X, POS_Z, VEL_Z; xlabel="time [s]", ylabels=["pos_z [m]", "vel_z [m/s]"],
labels=["pos_z [m]", "vel_z [m/s]"], fig="falling mass")
display(p)
```
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [September 21, 2024, 1:52pm UTC](https://discourse.julialang.org/t/modelingtoolkit-9-39-is-broken-9-40-1-works-well/119670/6 "2024-09-21T13:52:26Z")
It’s overdetermined because of the extra initial condition on the acceleration. That’s a computed value.
---
### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [September 21, 2024, 2:07pm UTC](https://discourse.julialang.org/t/modelingtoolkit-9-39-is-broken-9-40-1-works-well/119670/7 "2024-09-21T14:07:51Z")
And why was there no warning with MTK 9.38 ?
---
### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [September 21, 2024, 2:40pm UTC](https://discourse.julialang.org/t/modelingtoolkit-9-39-is-broken-9-40-1-works-well/119670/8 "2024-09-21T14:40:03Z")
@ChrisRackauckas Thanks a lot for the quick fix!
And the new warning is very useful, I could simplify my code a lot by remove redundant initializations, e.g.:
Old:
```julia
POS0, VEL0, ACC0, SEGMENTS0, UNIT_VECTORS0 = calc_initial_state(se)
mass_per_meter = se.rho_tether * π * (se.d_tether/2000.0)^2
@parameters c_spring0=se.c_spring/(se.l0/se.segments) l_seg=se.l0/se.segments
@parameters rel_compression_stiffness = se.rel_compression_stiffness
@variables pos(t)[1:3, 1:se.segments+1] = POS0
@variables vel(t)[1:3, 1:se.segments+1] = VEL0
@variables acc(t)[1:3, 1:se.segments+1] = ACC0
@variables segment(t)[1:3, 1:se.segments] = SEGMENTS0
@variables unit_vector(t)[1:3, 1:se.segments] = UNIT_VECTORS0
@variables length(t) = se.l0
@variables c_spring(t) = c_spring0
@variables damping(t) = se.damping / l_seg
@variables m_tether_particle(t) = mass_per_meter * l_seg
@variables norm1(t)[1:se.segments] = l_seg * ones(se.segments)
@variables rel_vel(t)[1:3, 1:se.segments] = zeros(3, se.segments)
@variables spring_vel(t)[1:se.segments] = zeros(se.segments)
@variables c_spr(t)[1:se.segments] = c_spring0 * ones(se.segments)
@variables spring_force(t)[1:3, 1:se.segments] = zeros(3, se.segments)
@variables v_apparent(t)[1:3, 1:se.segments] = zeros(3, se.segments)
@variables v_app_perp(t)[1:3, 1:se.segments] = zeros(3, se.segments)
@variables norm_v_app(t)[1:se.segments] = ones(se.segments)
@variables half_drag_force(t)[1:3, 1:se.segments] = zeros(3, se.segments)
@variables total_force(t)[1:3, 1:se.segments+1] = zeros(3, se.segments+1)
```
New:
```julia
POS0, VEL0 = calc_initial_state(se)
mass_per_meter = se.rho_tether * π * (se.d_tether/2000.0)^2
@parameters c_spring0=se.c_spring/(se.l0/se.segments) l_seg=se.l0/se.segments
@parameters rel_compression_stiffness = se.rel_compression_stiffness
@variables pos(t)[1:3, 1:se.segments+1] = POS0
@variables vel(t)[1:3, 1:se.segments+1] = VEL0
@variables acc(t)[1:3, 1:se.segments+1]
@variables segment(t)[1:3, 1:se.segments]
@variables unit_vector(t)[1:3, 1:se.segments]
@variables length(t)
@variables c_spring(t)
@variables damping(t)
@variables m_tether_particle(t)
@variables norm1(t)[1:se.segments]
@variables rel_vel(t)[1:3, 1:se.segments]
@variables spring_vel(t)[1:se.segments]
@variables c_spr(t)[1:se.segments]
@variables spring_force(t)[1:3, 1:se.segments]
@variables v_apparent(t)[1:3, 1:se.segments]
@variables v_app_perp(t)[1:3, 1:se.segments]
@variables norm_v_app(t)[1:se.segments]
@variables half_drag_force(t)[1:3, 1:se.segments]
@variables total_force(t)[1:3, 1:se.segments+1]
```