Sparse Polynomial Interpolation and the Fast Euclidean Algorithm

We introduce an algorithm to interpolate sparse multivariate polynomials with integer coefficients. Our algorithm modifies Ben-Or and Tiwari’s deterministic algorithm for interpolating over rings of characteristic zero to work modulo p, a smooth prime of our choice. We present benchmarks comparing our algorithm to Zippel’s probabilistic sparse interpolation algorithm, demonstrating that our algorithm makes fewer probes for sparse polynomials. Our interpolation algorithm requires finding roots of a polynomial in GF(p)[x], which in turn requires an efficient polynomial GCD algorithm. Motivated by this observation, we review the Fast Extended Euclidean algorithm for univariate polynomials, which recursively computes the GCD using a divide-and-conquer approach. We present benchmarks for our implementation of the classical and fast versions of the Euclidean algorithm demonstrating a good speedup. We discuss computing resultants as an application of the fast GCD algorithm.