# ModelingToolkit.jl cryptic error
**URL:** https://discourse.julialang.org/t/modelingtoolkit-jl-cryptic-error/57308
**Category:** Modelling & Simulations
**Tags:** question
**Created:** [March 16, 2021, 2:23pm UTC](https://discourse.julialang.org/t/modelingtoolkit-jl-cryptic-error/57308 "2021-03-16T14:23:28Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@ohmsweetohm1](https://discourse.julialang.org/u/ohmsweetohm1)
#### Post date: [March 16, 2021, 2:23pm UTC](https://discourse.julialang.org/t/modelingtoolkit-jl-cryptic-error/57308/1 "2021-03-16T14:23:29Z")
I was trying to model a thermo-fluid system with `ModelingToolkit.jl`, however I encountered this:
```julia
julia> prob = ODAEProblem(sys, Pair[], (0.0, 10.0))
ERROR: AssertionError: !(isalgvar(s, var))
```
What does it mean?
The connection equations are based on: [15 Stream Connectors‣ Modelica® Language Specification version 3.6-dev](https://specification.modelica.org/master/stream-connectors.html)
The equations before `structural_simplify`:
```julia
julia> model
Model model with 38 equations
States (42):
r1₊a₊mdot(t) [defaults to 0.0]
mixing_valve₊a₊mdot(t) [defaults to 0.0]
r1₊a₊p(t) [defaults to 100000.0]
⋮
Parameters (7):
r1₊p [defaults to 200000.0]
r1₊T [defaults to 353.15]
r2₊p [defaults to 200000.0]
⋮
julia> equations(model)
38-element Array{Equation,1}:
mixing_valve₊a₊mdot(t) + r1₊a₊mdot(t) ~ 0.0
r1₊a₊p(t) ~ mixing_valve₊a₊p(t)
r1₊a₊T_in_stream(t) ~ mixing_valve₊a₊T_outflow(t)
mixing_valve₊a₊T_in_stream(t) ~ r1₊a₊T_outflow(t)
mixing_valve₊b₊mdot(t) + r2₊a₊mdot(t) ~ 0.0
r2₊a₊p(t) ~ mixing_valve₊b₊p(t)
r2₊a₊T_in_stream(t) ~ mixing_valve₊b₊T_outflow(t)
mixing_valve₊b₊T_in_stream(t) ~ r2₊a₊T_outflow(t)
mixing_valve₊c₊mdot(t) + r3₊a₊mdot(t) ~ 0.0
mixing_valve₊c₊p(t) ~ r3₊a₊p(t)
mixing_valve₊c₊T_in_stream(t) ~ r3₊a₊T_outflow(t)
r3₊a₊T_in_stream(t) ~ mixing_valve₊c₊T_outflow(t)
r1₊a₊p(t) ~ r1₊p
r1₊a₊T_outflow(t) ~ r1₊T
r2₊a₊p(t) ~ r2₊p
r2₊a₊T_outflow(t) ~ r2₊T
mixing_valve₊valve_1₊A(t) ~ 7.0e-5mixing_valve₊y
mixing_valve₊valve_2₊A(t) ~ 7.0e-5(1 - mixing_valve₊y)
mixing_valve₊valve_1₊a₊mdot(t) - mixing_valve₊a₊mdot(t) ~ 0.0
mixing_valve₊a₊p(t) ~ mixing_valve₊valve_1₊a₊p(t)
mixing_valve₊a₊T_outflow(t) ~ mixing_valve₊valve_1₊a₊T_outflow(t)
mixing_valve₊valve_1₊a₊T_in_stream(t) ~ mixing_valve₊a₊T_in_stream(t)
mixing_valve₊valve_2₊a₊mdot(t) - mixing_valve₊b₊mdot(t) ~ 0.0
mixing_valve₊b₊p(t) ~ mixing_valve₊valve_2₊a₊p(t)
mixing_valve₊b₊T_outflow(t) ~ mixing_valve₊valve_2₊a₊T_outflow(t)
mixing_valve₊valve_2₊a₊T_in_stream(t) ~ mixing_valve₊b₊T_in_stream(t)
mixing_valve₊valve_1₊b₊mdot(t) + mixing_valve₊valve_2₊b₊mdot(t) - mixing_valve₊c₊mdot(t) ~ 0.0
mixing_valve₊valve_1₊b₊p(t) ~ mixing_valve₊valve_2₊b₊p(t)
mixing_valve₊valve_1₊b₊p(t) ~ mixing_valve₊c₊p(t)
mixing_valve₊valve_1₊b₊T_in_stream(t) ~ (mixing_valve₊c₊T_in_stream(t)*max(mixing_valve₊c₊mdot(t), 0) + mixing_valve₊valve_2₊b₊T_outflow(t)*max(-mixing_valve₊valve_2₊b₊mdot(t), 0))*((max(mixing_valve₊c₊mdot(t), 0) + max(-mixing_valve₊valve_2₊b₊mdot(t), 0))^-1)
mixing_valve₊valve_2₊b₊T_in_stream(t) ~ (mixing_valve₊c₊T_in_stream(t)*max(mixing_valve₊c₊mdot(t), 0) + mixing_valve₊valve_1₊b₊T_outflow(t)*max(-mixing_valve₊valve_1₊b₊mdot(t), 0))*((max(mixing_valve₊c₊mdot(t), 0) + max(-mixing_valve₊valve_1₊b₊mdot(t), 0))^-1)
mixing_valve₊c₊T_outflow(t) ~ (mixing_valve₊valve_1₊b₊T_outflow(t)*max(-mixing_valve₊valve_1₊b₊mdot(t), 0) + mixing_valve₊valve_2₊b₊T_outflow(t)*max(-mixing_valve₊valve_2₊b₊mdot(t), 0))*((max(-mixing_valve₊valve_1₊b₊mdot(t), 0) + max(-mixing_valve₊valve_2₊b₊mdot(t), 0))^-1)
mixing_valve₊valve_1₊a₊mdot(t) + mixing_valve₊valve_1₊b₊mdot(t) ~ 0
mixing_valve₊valve_1₊b₊mdot(t) ~ 44.67661580737735max(min(mixing_valve₊valve_1₊A(t), 7.0e-5), 1.0e-9)*regRoot(mixing_valve₊valve_1₊b₊p(t) - mixing_valve₊valve_1₊a₊p(t), 0.0005000000000000004(202650.0 + mixing_valve₊valve_1₊a₊p(t) + mixing_valve₊valve_1₊b₊p(t)))
mixing_valve₊valve_2₊a₊mdot(t) + mixing_valve₊valve_2₊b₊mdot(t) ~ 0
mixing_valve₊valve_2₊b₊mdot(t) ~ 44.67661580737735max(min(mixing_valve₊valve_2₊A(t), 7.0e-5), 1.0e-9)*regRoot(mixing_valve₊valve_2₊b₊p(t) - mixing_valve₊valve_2₊a₊p(t), 0.0005000000000000004(202650.0 + mixing_valve₊valve_2₊a₊p(t) + mixing_valve₊valve_2₊b₊p(t)))
r3₊a₊p(t) ~ r3₊p
r3₊a₊T_outflow(t) ~ r3₊T
```
and after
```julia
julia> sys = structural_simplify(model)
Model model with 1 equations
States (3):
mixing_valve₊valve_1₊b₊T_outflow(t) [defaults to 293.15]
mixing_valve₊valve_2₊b₊T_outflow(t) [defaults to 293.15]
mixing_valve₊valve_2₊b₊T_in_stream(t) [defaults to 293.15]
Parameters (7):
r1₊p [defaults to 200000.0]
r1₊T [defaults to 353.15]
r2₊p [defaults to 200000.0]
⋮
Incidence matrix:
[1, 1] = ×
[1, 3] = ×
julia> equations(sys)
1-element Array{Equation,1}:
0 ~ (r3₊T*max(44.67661580737735regRoot(r3₊p - r1₊p, 0.0005000000000000004(202650.0 + r1₊p + r3₊p))*max(min(7.0e-5mixing_valve₊y, 7.0e-5), 1.0e-9) + 44.67661580737735regRoot(r3₊p - r2₊p, 0.0005000000000000004(202650.0 + r2₊p + r3₊p))*max(min(7.0e-5(1 - mixing_valve₊y), 7.0e-5), 1.0e-9), 0) + mixing_valve₊valve_1₊b₊T_outflow(t)*max(-44.67661580737735regRoot(r3₊p - r1₊p, 0.0005000000000000004(202650.0 + r1₊p + r3₊p))*max(min(7.0e-5mixing_valve₊y, 7.0e-5), 1.0e-9), 0))*((max(44.67661580737735regRoot(r3₊p - r1₊p, 0.0005000000000000004(202650.0 + r1₊p + r3₊p))*max(min(7.0e-5mixing_valve₊y, 7.0e-5), 1.0e-9) + 44.67661580737735regRoot(r3₊p - r2₊p, 0.0005000000000000004(202650.0 + r2₊p + r3₊p))*max(min(7.0e-5(1 - mixing_valve₊y), 7.0e-5), 1.0e-9), 0) + max(-44.67661580737735regRoot(r3₊p - r1₊p, 0.0005000000000000004(202650.0 + r1₊p + r3₊p))*max(min(7.0e-5mixing_valve₊y, 7.0e-5),
1.0e-9), 0))^-1) - mixing_valve₊valve_2₊b₊T_in_stream(t)
```
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [March 16, 2021, 3:11pm UTC](https://discourse.julialang.org/t/modelingtoolkit-jl-cryptic-error/57308/2 "2021-03-16T15:11:09Z")
Open an issue for this. Could be a bug. Please share how to recreate it.
---
### Author:  [@ohmsweetohm1](https://discourse.julialang.org/u/ohmsweetohm1)
#### Post date: [March 16, 2021, 7:27pm UTC](https://discourse.julialang.org/t/modelingtoolkit-jl-cryptic-error/57308/3 "2021-03-16T19:27:12Z")
It is not, the model was missing four equations.
Is there a way to check the consistency of the model?
First thing might be if the number of equations and number of states are the same. But is this true in general.
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [March 16, 2021, 7:38pm UTC](https://discourse.julialang.org/t/modelingtoolkit-jl-cryptic-error/57308/4 "2021-03-16T19:38:35Z")
We’re adding a `check_consistency` fairly soon. See the issue on it.