# Define function

**URL:** <https://community.freefem.org/t/define-function/1036>\
**Category:** General Discussion\
**Created:** [June 15, 2021, 5:47pm UTC](https://community.freefem.org/t/define-function/1036 "2021-06-15T17:47:50Z")\
**Posts on this page:** 3\
**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:** [June 15, 2021, 5:47pm UTC](https://community.freefem.org/t/define-function/1036/1 "2021-06-15T17:47:50Z")

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Hi,  
how we define the function  
f(x,y,t=0)= a if |x-x\_0|^2+|y-y\_0|^2 \<= r^2 , 0 else  
a,x\_0 , y\_0 and r are real data.

Thank you in advance

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**Author:** ![julienG](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/julieng/32/222_2.png) [@julienG](https://community.freefem.org/u/julienG)\
**Post date:** [June 16, 2021, 7:53am UTC](https://community.freefem.org/t/define-function/1036/2 "2021-06-16T07:53:40Z")

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`f = ( (x-x0)^2+(y-y0)^2 <= r^2 ? a : 0 )`

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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:** [June 16, 2021, 8:04am UTC](https://community.freefem.org/t/define-function/1036/3 "2021-06-16T08:04:11Z")

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Thank you so much Julien G