# How to select a field in a specific area?

**URL:** https://community.freefem.org/t/how-to-select-a-field-in-a-specific-area/1659
**Category:** General Discussion
**Created:** [April 11, 2022, 8:34am UTC](https://community.freefem.org/t/how-to-select-a-field-in-a-specific-area/1659 "2022-04-11T08:34:57Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![chalmi](https://avatars.discourse-cdn.com/v4/letter/c/4af34b/32.png) [@chalmi](https://community.freefem.org/u/chalmi)
#### Post date: [April 11, 2022, 8:34am UTC](https://community.freefem.org/t/how-to-select-a-field-in-a-specific-area/1659/1 "2022-04-11T08:34:57Z")

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Hi everyone, I’m new here, and I need some help.  
I’m working on CSI (contrast source inversion method) which is an inverse scattering problem. In this method, I have to solve EDP this is why I use Freefem++. My domain is divided into 3 parts, I solve my problem in all the domain (Omega) but then I have to select my solution in only 1 part of the all domain, how can I do that in freefem ?  
Thank u.

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### Author: ![sumantkr](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/sumantkr/32/2681_2.png) [@sumantkr](https://community.freefem.org/u/sumantkr)
#### Post date: [April 21, 2022, 6:26am UTC](https://community.freefem.org/t/how-to-select-a-field-in-a-specific-area/1659/2 "2022-04-21T06:26:30Z")

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you can control the domain by specifying it.

eg. for a domain containing x = 1then

`(x<1)* expression + (x>=1)*someotherexpre`

it can define the two domains, first with less than 1 and other with greater than equal to a domain.