# Forced equality between two fields
**URL:** https://community.freefem.org/t/forced-equality-between-two-fields/1739
**Category:** General Discussion
**Created:** [May 13, 2022, 5:15pm UTC](https://community.freefem.org/t/forced-equality-between-two-fields/1739 "2022-05-13T17:15:53Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@mchetoui](https://community.freefem.org/u/mchetoui)
#### Post date: [May 13, 2022, 5:15pm UTC](https://community.freefem.org/t/forced-equality-between-two-fields/1739/1 "2022-05-13T17:15:53Z")
Hello every one,
I have a problem with 6 unknown fields (ux1,uy1,ux2,uy2,p1,p2) and 6 test functions (vx1,vy1,vx2,vy2,q1,q2). My geometry is a square (0,1)(0,1) divided in two equal rectangle by a vertical internal line at (x=0.5). I need to force the equality between the two fields ux1 and ux2 at the internal line. I tried to add the integral
int1d(Th, internal\_line)(q2\*(ux1-ux2))
but it doesn’t work. Is there a trick to do it?
Thank you.
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### Author:  [@frederichecht](https://community.freefem.org/u/frederichecht)
#### Post date: [May 16, 2022, 11:52am UTC](https://community.freefem.org/t/forced-equality-between-two-fields/1739/2 "2022-05-16T11:52:46Z")
They are lot of way to solve this problem,
Read Domain Decomposition technique,
And a Lagrange multiplier on border x=0.5.for exemple,
…