# Integral formula

**URL:** <https://community.freefem.org/t/integral-formula/864>\
**Category:** General Discussion\
**Created:** [March 19, 2021, 5:12pm UTC](https://community.freefem.org/t/integral-formula/864 "2021-03-19T17:12:39Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Aicha](https://avatars.discourse-cdn.com/v4/letter/a/ec9cab/32.png) [@Aicha](https://community.freefem.org/u/Aicha)\
**Post date:** [March 19, 2021, 5:12pm UTC](https://community.freefem.org/t/integral-formula/864/1 "2021-03-19T17:12:39Z")

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Hi,  
please hows we write in FF++, the formula:  
\int\_{t-\tau-h}^{t-\tau+h} I(x,s) ds  
?  
where h is an integer avec I(x,s) is function solution of an other problem

Regards

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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 20, 2021, 2:31pm UTC](https://community.freefem.org/t/integral-formula/864/2 "2021-03-20T14:31:36Z")

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The simple way to create a meshL Thl of size -h,h  
the you can also define a other meshL Th1 of size ???

now you have a function of xx

```
 func real ffff(real xx){return int1d(ThI)( I(xx,t-t-tau+x) );}
```