# Basic Syntax question

**URL:** https://community.freefem.org/t/basic-syntax-question/740
**Category:** General Discussion
**Created:** [January 11, 2021, 3:50pm UTC](https://community.freefem.org/t/basic-syntax-question/740 "2021-01-11T15:50:51Z")
**Posts on this page:** 3
**Page:** 1

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### Author: ![dajopez](https://avatars.discourse-cdn.com/v4/letter/d/a87d85/32.png) [@dajopez](https://community.freefem.org/u/dajopez)
#### Post date: [January 11, 2021, 3:50pm UTC](https://community.freefem.org/t/basic-syntax-question/740/1 "2021-01-11T15:50:51Z")

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How do I do boundary conditions where the normal derivative is set to 0 when solving differential equations?

Thank you for your help.

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### Author: ![LeonardoDipilato](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/leonardodipilato/32/361_2.png) [@LeonardoDipilato](https://community.freefem.org/u/LeonardoDipilato)
#### Post date: [January 11, 2021, 6:24pm UTC](https://community.freefem.org/t/basic-syntax-question/740/2 "2021-01-11T18:24:00Z")

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When you force the value of the derivative to be a certain value, you are using a **Neumann** boundary condition.  
In FEM, the Neumann boundary condition appear directly into the equation. You can find some examples on how to do that in the documentation.

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### Author: ![amtravco](https://avatars.discourse-cdn.com/v4/letter/a/13edae/32.png) [@amtravco](https://community.freefem.org/u/amtravco)
#### Post date: [January 12, 2021, 12:19am UTC](https://community.freefem.org/t/basic-syntax-question/740/3 "2021-01-12T00:19:01Z")

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I’m not completely sure about this, but my experience has been if you don’t explicitly use any condition on a boundary then the normal derivative becomes zero on that boundary.