# Detecting undefined list positions

**URL:** <https://cl.desmos.com/t/detecting-undefined-list-positions/5098>\
**Category:** Questions\
**Created:** [September 8, 2023, 6:23pm UTC](https://cl.desmos.com/t/detecting-undefined-list-positions/5098 "2023-09-08T18:23:26Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![Steve\_Heller](https://yyz1.discourse-cdn.com/flex031/user_avatar/cl.desmos.com/steve_heller/32/3539_2.png) [@Steve\_Heller](https://cl.desmos.com/u/Steve_Heller)\
**Post date:** [September 8, 2023, 6:23pm UTC](https://cl.desmos.com/t/detecting-undefined-list-positions/5098/1 "2023-09-08T18:23:26Z")

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There must be a better way:

> **[Detecting undefined table list positions](https://www.desmos.com/calculator/ejvcnn4ryo)**
>
> Explore math with our beautiful, free online graphing calculator. Graph functions, plot points, visualize algebraic equations, add sliders, animate graphs, and more.

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**Author:** ![SchuylerAlschuler](https://yyz1.discourse-cdn.com/flex031/user_avatar/cl.desmos.com/schuyleralschuler/32/3852_2.png) [@SchuylerAlschuler](https://cl.desmos.com/u/SchuylerAlschuler)\
**Post date:** [September 8, 2023, 6:42pm UTC](https://cl.desmos.com/t/detecting-undefined-list-positions/5098/2 "2023-09-08T18:42:53Z")

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Hey Steve,

One way to check for undefined values is checking that the absolute value of a value is greater than or equal to zero.

Hopefully [this](https://www.desmos.com/calculator/q8l8fy9jry) graph is helpful!

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<div class="post-metadata">

**Author:** ![Steve\_Heller](https://yyz1.discourse-cdn.com/flex031/user_avatar/cl.desmos.com/steve_heller/32/3539_2.png) [@Steve\_Heller](https://cl.desmos.com/u/Steve_Heller)\
**Post date:** [September 8, 2023, 6:53pm UTC](https://cl.desmos.com/t/detecting-undefined-list-positions/5098/3 "2023-09-08T18:53:50Z")

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Thanks, Schuyler,

cool trick!

Your graph was quite helpful!

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**Author:** ![Daniel\_Grubbs](https://yyz1.discourse-cdn.com/flex031/user_avatar/cl.desmos.com/daniel_grubbs/32/719_2.png) [@Daniel\_Grubbs](https://cl.desmos.com/u/Daniel_Grubbs)\
**Post date:** [September 12, 2023, 8:55pm UTC](https://cl.desmos.com/t/detecting-undefined-list-positions/5098/4 "2023-09-12T20:55:17Z")

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You also need to add infinity into your inequality… See [here](https://www.desmos.com/calculator/38uabbgbkj).

 ![image](https://canada1.discourse-cdn.com/flex031/uploads/desmos/original/2X/a/a6c138ba0f5f06b82080a5645ec9d4622b6df565.png)

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**Author:** ![Daniel\_Wekselgreene](https://yyz1.discourse-cdn.com/flex031/user_avatar/cl.desmos.com/daniel_wekselgreene/32/1819_2.png) [@Daniel\_Wekselgreene](https://cl.desmos.com/u/Daniel_Wekselgreene)\
**Post date:** [September 12, 2023, 9:29pm UTC](https://cl.desmos.com/t/detecting-undefined-list-positions/5098/5 "2023-09-12T21:29:13Z")

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I think you can also just do L[L=L]

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<div class="post-metadata">

**Author:** ![Daniel\_Grubbs](https://yyz1.discourse-cdn.com/flex031/user_avatar/cl.desmos.com/daniel_grubbs/32/719_2.png) [@Daniel\_Grubbs](https://cl.desmos.com/u/Daniel_Grubbs)\
**Post date:** [September 13, 2023, 5:22am UTC](https://cl.desmos.com/t/detecting-undefined-list-positions/5098/6 "2023-09-13T05:22:40Z")

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It doesn’t catch infinity. [https://www.desmos.com/calculator/f3vcm8hw0w](https://www.desmos.com/calculator/f3vcm8hw0w)

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<div class="post-metadata">

**Author:** ![Daniel\_Wekselgreene](https://yyz1.discourse-cdn.com/flex031/user_avatar/cl.desmos.com/daniel_wekselgreene/32/1819_2.png) [@Daniel\_Wekselgreene](https://cl.desmos.com/u/Daniel_Wekselgreene)\
**Post date:** [September 13, 2023, 6:17pm UTC](https://cl.desmos.com/t/detecting-undefined-list-positions/5098/7 "2023-09-13T18:17:35Z")

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Good to know! I never ran into that I guess.