On fast division algorithm for polynomials using newton iteration

  • Authors:
  • Zhengjun Cao;Hanyue Cao

  • Affiliations:
  • Department of Mathematics, Shanghai University, Shanghai, China;Department of Mathematics, Shanghai University, Shanghai, China

  • Venue:
  • ICICA'12 Proceedings of the Third international conference on Information Computing and Applications
  • Year:
  • 2012

Quantified Score

Hi-index 0.00

Visualization

Abstract

The classical division algorithm for polynomials requires O(n2) operations for inputs of size n. Using reversal technique and Newton iteration, it can be improved to O(M(n)), where M is a multiplication time. But the method requires that the degree of the modulo, xl, should be the power of 2. If l is not a power of 2 and f(0)=1, Gathen and Gerhard suggest to compute the inverse, f−1, modulo $x^{\lceil l/2^r\rceil}, x^{\lceil l/2^{r-1}\rceil}, \cdots, x^{\lceil l/2\rceil}, x^ l$ , separately. But they did not specify the iterative step. In this paper, we show that the original Newton iteration formula can be directly used to compute f−1 mod xl without any additional cost, when l is not a power of 2.