1,007 research outputs found
Algorithms for the indefinite and definite summation
The celebrated Zeilberger algorithm which finds holonomic recurrence
equations for definite sums of hypergeometric terms is extended to
certain nonhypergeometric terms. An expression is called a
hypergeometric term if both and are
rational functions. Typical examples are ratios of products of exponentials,
factorials, function terms, bin omial coefficients, and Pochhammer
symbols that are integer-linear with respect to and in their arguments.
We consider the more general case of ratios of products of exponentials,
factorials, function terms, binomial coefficients, and Pochhammer
symbols that are rational-linear with respect to and in their
arguments, and present an extended version of Zeilberger's algorithm for this
case, using an extended version of Gosper's algorithm for indefinite summation.
In a similar way the Wilf-Zeilberger method of rational function
certification of integer-linear hypergeometric identities is extended to
rational-linear hypergeometric identities
Computer algebra tools for Feynman integrals and related multi-sums
In perturbative calculations, e.g., in the setting of Quantum Chromodynamics
(QCD) one aims at the evaluation of Feynman integrals. Here one is often faced
with the problem to simplify multiple nested integrals or sums to expressions
in terms of indefinite nested integrals or sums. Furthermore, one seeks for
solutions of coupled systems of linear differential equations, that can be
represented in terms of indefinite nested sums (or integrals). In this article
we elaborate the main tools and the corresponding packages, that we have
developed and intensively used within the last 10 years in the course of our
QCD-calculations
Refined Holonomic Summation Algorithms in Particle Physics
An improved multi-summation approach is introduced and discussed that enables
one to simultaneously handle indefinite nested sums and products in the setting
of difference rings and holonomic sequences. Relevant mathematics is reviewed
and the underlying advanced difference ring machinery is elaborated upon. The
flexibility of this new toolbox contributed substantially to evaluating
complicated multi-sums coming from particle physics. Illustrative examples of
the functionality of the new software package RhoSum are given.Comment: Modified Proposition 2.1 and Corollary 2.
Evaluating parametric holonomic sequences using rectangular splitting
We adapt the rectangular splitting technique of Paterson and Stockmeyer to
the problem of evaluating terms in holonomic sequences that depend on a
parameter. This approach allows computing the -th term in a recurrent
sequence of suitable type using "expensive" operations at the cost
of an increased number of "cheap" operations.
Rectangular splitting has little overhead and can perform better than either
naive evaluation or asymptotically faster algorithms for ranges of
encountered in applications. As an example, fast numerical evaluation of the
gamma function is investigated. Our work generalizes two previous algorithms of
Smith.Comment: 8 pages, 2 figure
On hypergeometric series reductions from integral representations, the Kampe de Feriet function, and elsewhere
Single variable hypergeometric functions pFq arise in connection with the
power series solution of the Schrodinger equation or in the summation of
perturbation expansions in quantum mechanics. For these applications, it is of
interest to obtain analytic expressions, and we present the reduction of a
number of cases of pFp and p+1F_p, mainly for p=2 and p=3. These and related
series have additional applications in quantum and statistical physics and
chemistry.Comment: 17 pages, no figure
Hypergeometric-type sequences
We introduce hypergeometric-type sequences. They are linear combinations of interlaced hypergeometric sequences (of arbitrary interlacements). We prove that they form a subring of the ring of holonomic sequences. An interesting family of sequences in this class are those defined by trigonometric functions with linear arguments in the index and π, such as Chebyshev polynomials, sin2 (n π/4) · cos (n π/6))n , and compositions like (sin (cos(nπ/3)π))n . We describe an algorithm that computes a hypergeometric-type normal form of a given holonomic nth term whenever it exists. Our implementation enables us to generate several identities for terms defined via trigonometric function
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