> ## Documentation Index
> Fetch the complete documentation index at: https://docs.starknet.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Introduction

> This section introduces the Circle FFT algorithm, used to interpolate bivariate polynomials over the circle domain using a divide-and-conquer approach.

This section is organized as follows:

* **[Algorithm](/learn/S-two-book/how-it-works/circle-fft/algorithm)**: Overview of the Circle FFT algorithm with concrete examples showing the three-step interpolation process.
* **[Twiddles](/learn/S-two-book/how-it-works/circle-fft/twiddles)**: Precomputation and storage of twiddle values required for efficient FFT operations.
* **[Interpolate](/learn/S-two-book/how-it-works/circle-fft/interpolation)**: Detailed implementation walkthrough of the interpolation function with code breakdown.
* **[Basis and Dimension Gap](/learn/S-two-book/how-it-works/circle-fft/basis)**: FFT basis for Circle FFT and analysis of the dimension gap in circle polynomial spaces.