# The boundary condition in FreeFem

**URL:** https://community.freefem.org/t/the-boundary-condition-in-freefem/3932
**Category:** General Discussion
**Created:** [May 23, 2025, 11:57am UTC](https://community.freefem.org/t/the-boundary-condition-in-freefem/3932 "2025-05-23T11:57:44Z")
**Posts on this page:** 1
**Showing post:** 2

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### Author: ![fb77](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/fb77/32/3796_2.png) [@fb77](https://community.freefem.org/u/fb77)
#### Post date: [May 23, 2025, 8:33pm UTC](https://community.freefem.org/t/the-boundary-condition-in-freefem/3932/2 "2025-05-23T20:33:43Z")

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You can look at

> [@The boundary condition of Hall-MHD model](https://community.freefem.org/t/the-boundary-condition-of-hall-mhd-model/3484):
>
> Hello, everyone. Now I’m using freefem++ to solve the incompressible hall-MHD equations, but I’ve encountered a problem regarding the boundary conditions of the magnetic field. \mu\nabla\times (\nabla\times\mathbf{B})+(\mathbf{u}^n\cdot\nabla)\mathbf{B}^n-(\mathbf{B}^n\cdot\nabla)\mathbf{u}^n+\eta\nabla\times\left((\nabla\times\mathbf{B}^n)\times\mathbf{B}^n\right)=\mathbf{g} \nabla\cdot\mathbf{B}=0 Before solving, assume that the velocity field \mathbf{u}^n,\mathbf{B}^n is already known (I …

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