# Zero-flux boundary condition

**URL:** https://community.freefem.org/t/zero-flux-boundary-condition/2699
**Category:** General Discussion
**Created:** [September 11, 2023, 12:50pm UTC](https://community.freefem.org/t/zero-flux-boundary-condition/2699 "2023-09-11T12:50:52Z")
**Posts on this page:** 1
**Showing post:** 6

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### Author: ![cmd](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/cmd/32/67_2.png) [@cmd](https://community.freefem.org/u/cmd)
#### Post date: [September 12, 2023, 2:10pm UTC](https://community.freefem.org/t/zero-flux-boundary-condition/2699/6 "2023-09-12T14:10:04Z")

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It is due to numerical error. Your Neumann BC can only ever be as accurate as your discrete approximation of the derivatives. You can use a finer mesh or higher order elements if this is a problem, but I don’t expect errors of the order of 1e-9 to be an issue…

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