# Index of etak and Triangles

**URL:** <https://community.freefem.org/t/index-of-etak-and-triangles/25>\
**Category:** General Discussion\
**Created:** [April 13, 2019, 12:04pm UTC](https://community.freefem.org/t/index-of-etak-and-triangles/25 "2019-04-13T12:04:20Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![wys](https://avatars.discourse-cdn.com/v4/letter/w/9e8a1a/32.png) [@wys](https://community.freefem.org/u/wys)\
**Post date:** [April 13, 2019, 12:04pm UTC](https://community.freefem.org/t/index-of-etak-and-triangles/25/1 "2019-04-13T12:04:20Z")

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Dear all,

Another simple question arises when I run the **AdaptResidualErrorIndicator.edp**. I want to know the etak[i] corresponds to which element.

I think maybe for example eatk[0] corresponds to the first triangle introduced in .mesh file and eatk[1] corresponds to the seond, etc…

> Triangles  
> 72  
> 38 31 36 0  
> 38 30 31 0  
> 40 41 36 0  
> 29 30 38 0  
> 37 38 41 0  
> …

Am I right?

Thanks for your time.

wys

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**Author:** ![simon.garnotel](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/simon.garnotel/32/11_2.png) [@simon.garnotel](https://community.freefem.org/u/simon.garnotel)\
**Post date:** [April 16, 2019, 7:58am UTC](https://community.freefem.org/t/index-of-etak-and-triangles/25/2 "2019-04-16T07:58:03Z")

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In [AdaptResidualErrorIndicator.edp](https://github.com/FreeFem/FreeFem-sources/blob/master/examples/tutorial/AdaptResidualErrorIndicator.edp), `etak[][i]` correspond to the degree of freedom `i` of your finite element space. If you have a `P1` finite element space, that correspond to the vertex `i`