# About element integrals

**URL:** https://community.freefem.org/t/about-element-integrals/3032
**Category:** Feature Request
**Created:** [March 12, 2024, 1:08pm UTC](https://community.freefem.org/t/about-element-integrals/3032 "2024-03-12T13:08:36Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![LXX](https://avatars.discourse-cdn.com/v4/letter/l/258eb7/32.png) [@LXX](https://community.freefem.org/u/LXX)
#### Post date: [March 12, 2024, 1:08pm UTC](https://community.freefem.org/t/about-element-integrals/3032/1 "2024-03-12T13:08:36Z")

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I want to know how to implement this expression:  
 ![屏幕截图 2024-03-09 181236](https://canada1.discourse-cdn.com/flex030/uploads/freefem/original/2X/d/d83fb3698436fdf6325185b5d05cc1df712a915a.png)

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<div class="post-metadata">

### 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 13, 2024, 8:42am UTC](https://community.freefem.org/t/about-element-integrals/3032/2 "2024-03-13T08:42:14Z")

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First what is \tau\_1  
but you can do some think like

```auto
mesh Th=square(1à?10);// def of Omega_h
fespace Ph(Th,P0); // to define tau1 constant by triangle
fespace Vh(Th,P1) ; // for ph and ph star
Ph tau = 1 ; // here def value tau 
macro grad(u) [dx(u),dy(u)]//EOM 
varf vexp(p,pp) = int2d(Th)( grad(p)'*grad(pp)*tau) ;
matrix Mat = vexe(Vh,Vh); // matrix associated to Bilinear form vexp

```