# MethodOfLines & Boundary Conditions
**URL:** https://discourse.julialang.org/t/methodoflines-boundary-conditions/111393
**Category:** Modelling & Simulations
**Created:** [March 9, 2024, 7:47am UTC](https://discourse.julialang.org/t/methodoflines-boundary-conditions/111393 "2024-03-09T07:47:11Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@BLI](https://discourse.julialang.org/u/BLI)
#### Post date: [March 9, 2024, 7:47am UTC](https://discourse.julialang.org/t/methodoflines-boundary-conditions/111393/1 "2024-03-09T07:47:11Z")
I have a PDE system with:
- 3 PDEs
- A number of additional algebraic equations
- I have boundary and initial value conditions with a number of added algebraic equations to describe the boundary conditions
When I try to _discretize_ the system, I get an error message on boundary conditions:
```julia
AssertionError: Boundary condition ṁ_a2t(t) ~ Y_a2t(t)*sqrt((max(Δp_a2t(t), 0)*ρ_a(t)) / (p_at2 __ς*ρ_a2t__ ς))*f_v(u_a2t(t))*ṁ_a2t__c is not on a boundary of the domain, or is not a valid boundary condition
```
Here is the relevant model of the intended boundary condition:
Does the discretizer have a problem with inserting the expression for pressure difference, etc.?
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [March 9, 2024, 1:32pm UTC](https://discourse.julialang.org/t/methodoflines-boundary-conditions/111393/2 "2024-03-09T13:32:36Z")
Can you open an issue?
---
### Author:  [@BLI](https://discourse.julialang.org/u/BLI)
#### Post date: [March 9, 2024, 3:15pm UTC](https://discourse.julialang.org/t/methodoflines-boundary-conditions/111393/3 "2024-03-09T15:15:51Z")
Will do.