arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1101.4369cs.SCcs.MScs.NAmath.AGmath.NA
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扩张域上的一元实根隔离

Univariate real root isolation in an extension field

Adam Strzebonski, Elias Tsigaridas

摘要:

我们提出的算法,复杂性和实现结果的问题隔离的一元多项式的实根在$B_α \in L[y]$,其中$L=\QQ(α)$是一个简单的代数扩展的有理数。我们考虑两种方法来解决这个问题。在第一种方法中,使用结果计算,我们执行一个减少到一个多项式的整数系数。我们计算的根的分离界限,并使用它们,我们推断,我们可以隔离在$\sOB(N^{10})$,其中$N$是上界的输入多项式的所有数量(次数和位大小)的$B_α$的实根。在第二种方法中,我们隔离了直接作用于输入多项式的实根。我们计算改进的分离界的真正的根,我们证明他们是最佳的,在温和的假设。为了隔离的根,我们考虑修改的Sturm算法,和Sagraloff介绍的\func{descartes}算法的修改版本。对于前者,我们证明了$\sOB(N^8)$的复杂性界,对于后者,我们证明了$\sOB(N^{7})$的复杂性界.我们实现的算法在\func{C}的核心库的\mathematica的一部分,我们说明了他们的效率在各种数据集。最后,我们提出的复杂性结果的第一种方法,其中系数属于多个扩展的一般情况下。

英文摘要:

We present algorithmic, complexity and implementation results for the problem of isolating the real roots of a univariate polynomial in $B_α \in L[y]$, where $L=\QQ(α)$ is a simple algebraic extension of the rational numbers. We consider two approaches for tackling the problem. In the first approach using resultant computations we perform a reduction to a polynomial with integer coefficients. We compute separation bounds for the roots, and using them we deduce that we can isolate the real roots of $B_α$ in $\sOB(N^{10})$, where $N$ is an upper bound on all the quantities (degree and bitsize) of the input polynomials. In the second approach we isolate the real roots working directly on the polynomial of the input. We compute improved separation bounds for real roots and we prove that they are optimal, under mild assumptions. For isolating the roots we consider a modified Sturm's algorithm, and a modified version of \func{descartes}' algorithm introduced by Sagraloff. For the former we prove a complexity bound of $\sOB(N^8)$ and for the latter a bound of $\sOB(N^{7})$. We implemented the algorithms in \func{C} as part of the core library of \mathematica and we illustrate their efficiency over various data sets. Finally, we present complexity results for the general case of the first approach, where the coefficients belong to multiple extensions.

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