
MITACS Seminar Series on Mathematics of Computer Algebra and AnalysisSparse Polynomial Interpolation.Michael Monagan, Department of Mathematics, Simon Fraser University
Abstract: Let f be a polynomial in R[x1,x2,...,xn] of degree d with t nonzero terms which is represented as a "black box", i.e., all we can do is evaluate f at a point (a1,a2,...,an) in R^n. We call this ``probing'' the black box and we seek algorithms to interpolate f which minimize the number of probes (values). Consider f = 1 + x1^d + x2^d + ... + xn^d We can interpolate f from (d+1)^n values (probes) using Newton interpolation. But this is exponential in n and since multivariate polynomials in practice are usually sparse, that is, t << (d+1)^n, we seek algorithms which do a polynomial number of probes in t, n and d. In this talk we will present several previous methods, including o Richard Zippel's probabilistic method for R = Zp from 1979, o BenOr and Tiwari's deterministic method from 1988 for R = Z, o Huang and Rao's parallel method for small finite fields from 1999, o Kaltofen, Lee and Lobo's racing algorithm from 2000 for R = Zp. Zippel's algorithm is used by Maple, Magma and Mathemtica for polynomial GCD computation over Z. It makes O(ndt) probes. For algorithms which need to interpolate over R = Zp, Kaltofen, Lee and Lobo's method is the most efficient method (makes O(nt) probes) but it is highly sequential. We present a new parallel method which attains the same (O(nt) values). We have present also benchmarks comparing our algorithm with Zippel's. This is joint work with Mahdi Javadi. 