# Prescribe a value for a fixed point

**URL:** <https://community.freefem.org/t/prescribe-a-value-for-a-fixed-point/884>\
**Category:** General Discussion\
**Created:** [March 31, 2021, 6:47pm UTC](https://community.freefem.org/t/prescribe-a-value-for-a-fixed-point/884 "2021-03-31T18:47:01Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![yongxing](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/yongxing/32/3632_2.png) [@yongxing](https://community.freefem.org/u/yongxing)\
**Post date:** [March 31, 2021, 6:47pm UTC](https://community.freefem.org/t/prescribe-a-value-for-a-fixed-point/884/1 "2021-03-31T18:47:01Z")

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Is there a method to do this in FreeFEM++?

For example, fix the velocity at the centre of a disc so that it can keep rotating stably, or give a pressure reference point for a flow problem.

Some one suggested do **u[][n]=the value**. I have tried this, and found that u[][n] was erased after solving the FEM system.

Thank you for any thought in advance!