# Evaluating a polynomial in Chebyshev series

**URL:** <https://openfhe.discourse.group/t/evaluating-a-polynomial-in-chebyshev-series/1202>\
**Category:** Library Questions\
**Created:** [April 16, 2024, 5:58pm UTC](https://openfhe.discourse.group/t/evaluating-a-polynomial-in-chebyshev-series/1202 "2024-04-16T17:58:03Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![narger](https://yyz1.discourse-cdn.com/flex031/user_avatar/openfhe.discourse.group/narger/32/420_2.png) [@narger](https://openfhe.discourse.group/u/narger)\
**Post date:** [April 16, 2024, 5:58pm UTC](https://openfhe.discourse.group/t/evaluating-a-polynomial-in-chebyshev-series/1202/1 "2024-04-16T17:58:03Z")

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Hello there! 🙂

I want to evaluate a polynomial with very large and sparse coefficients found using Remez algorithm.  
I know that performing a transformation from power base to Chebyshev series outputs smaller coefficients (AFAIK, the modular reduction in bootstrapping exploits this observation).

If I transform my coefficients in Chebyshev series, can I use some high level API to evaluate the polynomial? I guess EvalPolyPS requires power base coefficients…

Thank you very much

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**Author:** ![muthu](https://avatars.discourse-cdn.com/v4/letter/m/bbce88/32.png) [@muthu](https://openfhe.discourse.group/u/muthu)\
**Post date:** [April 16, 2024, 10:11pm UTC](https://openfhe.discourse.group/t/evaluating-a-polynomial-in-chebyshev-series/1202/2 "2024-04-16T22:11:14Z")

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looking at the reply to question on atan2 etc. ( [How can i calculate terms like atan2?](https://openfhe.discourse.group/t/how-can-i-calculate-terms-like-atan2/1170) ) it seems the API the call is supported:

 ![image](https://canada1.discourse-cdn.com/flex031/uploads/openfhe/original/1X/8be78a21bf9b01ee1cecd328fb3b5f9d2049ca7e.png)

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**Author:** ![narger](https://yyz1.discourse-cdn.com/flex031/user_avatar/openfhe.discourse.group/narger/32/420_2.png) [@narger](https://openfhe.discourse.group/u/narger)\
**Post date:** [April 17, 2024, 6:45am UTC](https://openfhe.discourse.group/t/evaluating-a-polynomial-in-chebyshev-series/1202/3 "2024-04-17T06:45:14Z")

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My bad, I did not look well in the documentation, thank you very much!