# Non-linear elasticity Example

**URL:** https://community.freefem.org/t/non-linear-elasticity-example/427
**Category:** General Discussion
**Created:** [May 22, 2020, 8:57pm UTC](https://community.freefem.org/t/non-linear-elasticity-example/427 "2020-05-22T20:57:32Z")
**Posts on this page:** 3
**Page:** 1

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### Author: ![geoyanzhan3](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/geoyanzhan3/32/147_2.png) [@geoyanzhan3](https://community.freefem.org/u/geoyanzhan3)
#### Post date: [May 22, 2020, 8:57pm UTC](https://community.freefem.org/t/non-linear-elasticity-example/427/1 "2020-05-22T20:57:32Z")

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Hi FreeFEM team,

In the line 124 of the code for the Non-linear elasticity Example ([https://doc.freefem.org/models/non-linear-elasticity.html](https://doc.freefem.org/models/non-linear-elasticity.html)), why only “un” is updated? Why we don’t need to update “vn” (e.g., vn[] -= vv[]😉

Thank you very much,  
Yan

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### Author: ![prj](https://avatars.discourse-cdn.com/v4/letter/p/ecae2f/32.png) [@prj](https://community.freefem.org/u/prj)
#### Post date: [May 23, 2020, 5:23am UTC](https://community.freefem.org/t/non-linear-elasticity-example/427/2 "2020-05-23T05:23:52Z")

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Please read the [documentation](https://doc.freefem.org/documentation/finite-element.html#vector-valued-fe-function), especially the “Warning” paragraph of the linked section.

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### Author: ![geoyanzhan3](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/geoyanzhan3/32/147_2.png) [@geoyanzhan3](https://community.freefem.org/u/geoyanzhan3)
#### Post date: [May 23, 2020, 2:04pm UTC](https://community.freefem.org/t/non-linear-elasticity-example/427/3 "2020-05-23T14:04:16Z")

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Oh, I see. Thank you!