# How to check if a number is undefined

**URL:** <https://cl.desmos.com/t/how-to-check-if-a-number-is-undefined/3903>\
**Category:** Questions\
**Created:** [December 13, 2021, 5:40pm UTC](https://cl.desmos.com/t/how-to-check-if-a-number-is-undefined/3903 "2021-12-13T17:40:06Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Ian\_King](https://yyz1.discourse-cdn.com/flex031/user_avatar/cl.desmos.com/ian_king/32/3210_2.png) [@Ian\_King](https://cl.desmos.com/u/Ian_King)\
**Post date:** [December 13, 2021, 5:40pm UTC](https://cl.desmos.com/t/how-to-check-if-a-number-is-undefined/3903/1 "2021-12-13T17:40:06Z")

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I am attempting to make a physics engine in desmos (weehoo) using gravity with a list of points and I need to check for if a value in the list is undefined. How would I go about doing this?

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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:** [December 13, 2021, 8:30pm UTC](https://cl.desmos.com/t/how-to-check-if-a-number-is-undefined/3903/2 "2021-12-13T20:30:38Z")

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Do you need to know which one specifically is undefined? Or do you just need to exclude it from the list? Within a graph, you can exclude undefined items in a list by defining a new list in this manner:

> **[Desmos | Graphing Calculator](https://www.desmos.com/calculator/vmn5xoo1i6)**

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<div class="post-metadata">

**Author:** ![Ian\_King](https://yyz1.discourse-cdn.com/flex031/user_avatar/cl.desmos.com/ian_king/32/3210_2.png) [@Ian\_King](https://cl.desmos.com/u/Ian_King)\
**Post date:** [December 14, 2021, 5:02pm UTC](https://cl.desmos.com/t/how-to-check-if-a-number-is-undefined/3903/3 "2021-12-14T17:02:12Z")

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Thank you for your response.