Bimonotone enumeration
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- by Michael Eisermann PDF
- Math. Comp. 78 (2009), 591-613 Request permission
Abstract:
Solutions of a diophantine equation $f(a,b) = g(c,d)$, with $a,b,c,d$ in some finite range, can be efficiently enumerated by sorting the values of $f$ and $g$ in ascending order and searching for collisions. This article considers functions $f \colon \mathbb {N} \times \mathbb {N}\to \mathbb {Z}$ that are bimonotone in the sense that $f(a,b) \le f(a’,b’)$ whenever $a \le a’$ and $b \le b’$. A two-variable polynomial with non-negative coefficients is a typical example. The problem is to efficiently enumerate all pairs $(a,b)$ such that the values $f(a,b)$ appear in increasing order. We present an algorithm that is memory-efficient and highly parallelizable. In order to enumerate the first $n$ values of $f$, the algorithm only builds up a priority queue of length at most $\sqrt {2n}+1$. In terms of bit-complexity this ensures that the algorithm takes time $O( n \log ^2 n )$ and requires memory $O( \sqrt {n} \log n )$, which considerably improves on the memory bound $\Theta ( n \log n )$ provided by a naïve approach, and extends the semimonotone enumeration algorithm previously considered by R.L. Ekl and D.J. Bernstein.References
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Additional Information
- Michael Eisermann
- Affiliation: Institut Fourier, Université Grenoble I, France
- Email: Michael.Eisermann@ujf-grenoble.fr
- Received by editor(s): July 27, 2005
- Received by editor(s) in revised form: June 22, 2007
- Published electronically: June 16, 2008
- © Copyright 2008
American Mathematical Society
The copyright for this article reverts to public domain 28 years after publication. - Journal: Math. Comp. 78 (2009), 591-613
- MSC (2000): Primary 68P10; Secondary 11Y50, 68W10, 11Y16, 11D45
- DOI: https://doi.org/10.1090/S0025-5718-08-02162-5
- MathSciNet review: 2448723