# Pressure boundary condition

**URL:** <https://community.freefem.org/t/pressure-boundary-condition/1620>\
**Category:** General Discussion\
**Created:** [March 23, 2022, 7:38pm UTC](https://community.freefem.org/t/pressure-boundary-condition/1620 "2022-03-23T19:38:21Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![zese](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/zese/32/917_2.png) [@zese](https://community.freefem.org/u/zese)\
**Post date:** [March 23, 2022, 7:38pm UTC](https://community.freefem.org/t/pressure-boundary-condition/1620/1 "2022-03-23T19:38:21Z")

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Dear all

I have a basic question. In Freefem++ the equations are solved in matrix-forming method which is different with time stepping method. As I got from Navier-Stokes example in tutorial, the pressure is modelled by the continuity equation. Is that why for boundary conditions the velocity conditions are enough?

Best regards

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**Author:** ![frederichecht](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/frederichecht/32/15_2.png) [@frederichecht](https://community.freefem.org/u/frederichecht)\
**Post date:** [March 24, 2022, 2:25pm UTC](https://community.freefem.org/t/pressure-boundary-condition/1620/2 "2022-03-24T14:25:44Z")

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Because the pressure is a Lagrange multiplier