Kummer Hypergeometric Functions Research Articles

Over-order multiplicities and their application in controlling delay dynamics. On zeros’ distribution of linear combinations of Kummer hypergeometric functions

A series of recent works have shown that, for a system of linear functional differential equations, a spectral value having a multiplicity exceeding the order of the system tends to correspond to the spectral abscissa of the system, a property called MID for multiplicity-induced-dominancy. In particular, when this multiplicity coincides with the degree of the characteristic quasipolynomial, this property is called generic MID (GMID), in opposition to the intermediate MID (IMID), which corresponds to a multiplicity strictly smaller than the degree. The GMID has been fully characterized for single-delay retarded as well as neutral delay-differential equations thanks to the representation of the corresponding quasipolynomial in terms of a Kummer hypergeometric function. However, apart from partial results, in full generality, no result of the literature enables the characterization of the dominance of a spectral value having an intermediate multiplicity, which is essentially due to the lack of existing results among the open literature pertaining to linear combinations of Kummer functions’ zeros distribution. In this work, we overcome this difficulty and we further investigate the MID to cover the so-called over-order MID, that is, the cases where the multiplicity is larger than the order of the corresponding differential equation.

Nonlinear-cost random walk: Exact statistics of the distance covered for fixed budget.

We consider the nonlinear-cost random-walk model in discrete time introduced in Phys. Rev. Lett. 130, 237102 (2023)10.1103/PhysRevLett.130.237102, where a fee is charged for each jump of the walker. The nonlinear cost function is such that slow or short jumps incur a flat fee, while for fast or long jumps the cost is proportional to the distance covered. In this paper we compute analytically the average and variance of the distance covered in n steps when the total budget C is fixed, as well as the statistics of the number of long or short jumps in a trajectory of length n, for the exponential jump distribution. These observables exhibit a very rich and nonmonotonic scaling behavior as a function of the variable C/n, which is traced back to the makeup of a typical trajectory in terms of long or short jumps, and the resulting entropy thereof. As a by-product, we compute the asymptotic behavior of ratios of Kummer hypergeometric functions when both the first and last arguments are large. All our analytical results are corroborated by numerical simulations.

Does the exponential Wells-Riley model provide a good fit for human coronavirus and rhinovirus? A comparison of four dose-response models based on human challenge data.

The risk assessments during the COVID-19 pandemic were primarily based on dose-response models derived from the pooled datasets for infection of animals susceptible to SARS-CoV. Despite similarities, differences in susceptibility between animals and humans exist for respiratory viruses. The two most commonly used dose-response models for calculating the infection risk of respiratory viruses are the exponential and the Stirling approximated β-Poisson (BP) models. The modified version of the one-parameter exponential model or the Wells-Riley model was almost solely used for infection risk assessments during the pandemic. Still, the two-parameter (α and β) Stirling approximated BP model is often recommended compared to the exponential dose-response model due to its flexibility. However, the Stirling approximation restricts this model to the general rules of β≫1 and α≪β, and these conditions are very often violated. To refrain from these requirements, we tested a novel BP model by using the Laplace approximation of the Kummer hypergeometric function instead of the conservative Stirling approximation. The datasets of human respiratory airborne viruses available in the literature for human coronavirus (HCoV-229E) and human rhinovirus (HRV-16 and HRV-39) are used to compare the four dose-response models. Based on goodness-of-fit criteria, the exponential model was the best fitting model for the HCoV-229E (k=0.054) and for HRV-39 datasets (k=1.0), whereas the Laplace approximated BP model followed by the exact and Stirling approximated BP models are preferred for both the HRV-16 (α=0.152 and β=0.021 for Laplace BP) and the HRV-16 and HRV-39 pooled datasets (α=0.2247 and β=0.0215 for Laplace BP).

Behavior of Love-Wave Fields Due to the Reinforcement, Porosity Distributions, Non-Local Elasticity and Irregular Boundary Surfaces

Investigations are carried out to predict the characteristic behavior of Love-wave fields propagating in a non-local elastic model under the effects of irregular boundary surfaces, reinforcement, and porosity distributions. The model includes an anisotropic fiber-reinforced medium lying over an anisotropic porous half-space. Two different porosity distributions are investigated within the porous half-space, namely uniform porosity and asymmetrical porosity. Analytical solutions to the displacement fields for both the upper layer and the lower porous half-space are calculated. Solutions to the latter porosity distribution are obtained by using the asymptotic expansions of the Kummer hypergeometric functions of the second kind. Both the interface and the upper surface of the two-layered media are subjected to irregular boundary conditions, which leads to a complex form of the dispersion relation. We analyze the phase velocity and damped velocity behavior of the traveling Love-wave fields separately by using the real and imaginary components of the velocity dispersion relation. The calculated phase velocity curves obtained at the same parameters have been compared to demonstrate the accuracy of the established model. The effects of corrugation parameters, porosity distributions, non-local elasticity, and reinforcement on the phase velocity and the damped velocity curves are analyzed in detail using MATLAB software.

Padé Approximation and Hypergeometric Functions: A Missing Link with the Spectrum of Delay-Differential Equations

It is well known that rational approximation theory involves degenerate hyperge-ometric functions and, in particular, the Padé approximation of the exponential function is closely related to Kummer hypergeometric functions. Recently, in the context of the study of the exponential stability of the trivial solution of delay-differential equations, a new link between the degenerate hypergeometric function and the zeros distribution of the characteristic function associated with linear delay-differential equations was emphasized. Such a link allowed the characterization of a property of time-delay systems known as multiplicity-induced-dominancy (MID), which opened a new direction in designing low-complexity controllers for time-delay systems by using a partial pole placement idea. Thanks to their relations to hypergeometric functions, we explore in this paper links between the spectrum of delay-differential equations and Padé approximations of the exponential function. This note exploits and further comments recent results from [I. Boussaada, G. Mazanti and S-I. Niculescu. 2022, Comptes Rendus. Mathématique] and [I. Boussaada, G. Mazanti and S-I. Niculescu. 2022, Bulletin des Sciences Mathématiques].

Some remarks on the location of non-asymptotic zeros of Whittaker and Kummer hypergeometric functions

This paper focuses on the location of the non-asymptotic zeros of Whittaker and Kummer confluent hypergeometric functions. Based on a technique proposed by E. Hille for the analysis of solutions of some second-order ordinary differential equations, we characterize the sign of the real part of zeros of Whittaker and Kummer functions and provide estimates on the regions of the complex plane where those zeros can be located. Our main result is a correction of a previous statement by G. E. Tsvetkov whose propagation has induced mistakes in the literature. In particular, we review some results of E. B. Saff and R. S. Varga on the error of Padé's rational approximation of the exponential function, which are based on the latter.

Fuzzy Differential Subordinations Obtained Using a Hypergeometric Integral Operator

This paper is related to notions adapted from fuzzy set theory to the field of complex analysis, namely fuzzy differential subordinations. Using the ideas specific to geometric function theory from the field of complex analysis, fuzzy differential subordination results are obtained using a new integral operator introduced in this paper using the well-known confluent hypergeometric function, also known as the Kummer hypergeometric function. The new hypergeometric integral operator is defined by choosing particular parameters, having as inspiration the operator studied by Miller, Mocanu and Reade in 1978. Theorems are stated and proved, which give corollary conditions such that the newly-defined integral operator is starlike, convex and close-to-convex, respectively. The example given at the end of the paper proves the applicability of the obtained results.

Multiple zeta values for classical special functions

We compute multiple zeta values (MZVs) built from the zeros of various entire functions, usually special functions with physical relevance. In the usual case, MZVs and their linear combinations are evaluated using a morphism between symmetric functions and multiple zeta values. We show that this technique can be extended to the zeros of any entire function, and as an illustration, we explicitly compute some MZVs based on the zeros of Bessel, Airy, and Kummer hypergeometric functions. We highlight several approaches to the theory of MZVs, such as exploiting the orthogonality of various polynomials and fully utilizing the Weierstrass representation of an entire function. On the way, an identity for Bernoulli numbers by Gessel and Viennot is revisited and generalized to Bessel–Bernoulli polynomials, and the classical Euler identity between the Bernoulli numbers and Riemann zeta function at even argument is extended to this same class.

Characterization of Kummer hypergeometric Bernoulli polynomials and applications

In this paper, we present two characterizations of the sequences of Kummer hypergeometric polynomials Ba,b,n(x) and Kummer hypergeometric polynomials of the second kind Ka,b,n(x), which are respectively defined by the exponential generating functions:extM(a,a+b;t)=∑n=0∞Ba,b,n(x)tnn! and extU(a,a+b;t)=∑n=0∞Ka,b,n(x)tnn! with M(a,b;t)=∑n=0∞(a)n(b)ntnn!, where U(a,a+b;t) is the Kummer hypergeometric function of the second kind.First we construct Gauss–Weierstrass-type convolution operators Twa,b with a well-chosen kernel (density) function for each sequence of Kummer hypergeometric polynomials and for Kummer hypergeometric polynomials of the second kind. Then we characterize Kummer hypergeometric polynomials as the only Appell polynomials having a weighted-integral mean equal to zero. Our approach is inspired by the Gauss–Weierstrass convolution transform for Hermite polynomials and the Kummer integral representation for confluent hypergeometric functions.

Hypergeometric first integrals of the Duffing and van der Pol oscillators

The autonomous Duffing oscillator, and its van der Pol modification, are known to admit time-dependent first integrals for specific values of parameters. This corresponds to the existence of Darboux polynomials, and in fact more can be shown: that there exist Liouvillian first integrals which do not depend on time. They can be expressed in terms of the Gauss and Kummer hypergeometric functions, and are neither analytic, algebraic nor meromorphic. A criterion for this to happen in a general dynamical system is formulated as well.

Revisiting diffusion: Self-similar solutions and the 𝑡^{-1/2} decay in initial and initial-boundary value problems

The diffusion equation is a universal and standard textbook model for partial differential equations (PDEs). In this work, we revisit its solutions, seeking, in particular, self-similar profiles. This problem connects to the classical theory of special functions and, more specifically, to the Hermite as well as the Kummer hypergeometric functions. Reconstructing the solution of the original diffusion model from self-similar solutions of the associated self-similar PDE, we infer that thet−1/2t^{-1/2}decay law of the diffusion amplitude isnot necessary. In particular, it is possible to engineer setups ofboththe Cauchy problem and the initial-boundary value problem in which the solution decays at adifferent rate. Nevertheless, we observe that thet−1/2t^{-1/2}rate corresponds to the dominant decay mode among integrable initial data, i.e., ones corresponding to finite mass. Hence, unless the projection to such a mode is eliminated, generically this decay will be the slowest one observed. In initial-boundary value problems, an additional issue that arises is whether the boundary data areconsonantwith the initial data; namely, whether the boundary data agree at all times with the solution of the Cauchy problem associated with the same initial data, when this solution is evaluated at the boundary of the domain. In that case, the power law dictated by the solution of the Cauchy problem will be selected. On the other hand, in the non-consonant cases a decomposition of the problem into a self-similar and a non-self-similar one is seen to be beneficial in obtaining a systematic understanding of the resulting solution.

The Klein–Gordon–Fock equation in the curved spacetime of the Kerr–Newman (anti) de Sitter black hole

Exact solutions of the Klein–Gordon–Fock (KGF) general relativistic equation that describe the dynamics of a massive, electrically charged scalar particle in the curved spacetime geometry of an electrically charged, rotating Kerr–Newman–(anti) de Sitter black hole are investigated. In the general case of a rotating, charged, cosmological black hole the solution of the KGF equation with the method of separation of variables results in Fuchsian differential equations for the radial and angular parts which for most of the parameter space contain more than three finite singularities and thereby generalise the Heun differential equations. For particular values of the physical parameters (i.e. mass of the scalar particle) these Fuchsian equations reduce to the case of the Heun equation and the closed form analytic solutions we derive are expressed in terms of Heun functions. For other values of the parameters some of the extra singular points are false singular points. We derive the conditions on the coefficients of the generalised Fuchsian equation such that a singular point is a false point. In such a case the exact solution of the Fuchsian equation can in principle be simplified and expressed in terms of Heun functions. This is the generalisation of the case of a Heun equation with a false singular point in which the exact solution of Heun’s differential equation is expressed in terms of Gauß hypergeometric function. We also derive the exact solutions of the radial and angular equations for a charged massive scalar particle in the Kerr–Newman spacetime. The analytic solutions are expressed in terms of confluent Heun functions. Moreover, we derived the constraints on the parameters of the theory such that the solution simplifies and expressed in terms of confluent Kummer hypergeometric functions. We also investigate the radial solutions in the KN case in the regions near the event horizon and far from the black hole. Finally, we construct several expansions of the solutions of the Heun equation in terms of generalised hypergeometric functions of Lauricella–Appell.

Proofs of some conjectures on monotonicity of ratios of Kummer, Gauss and generalized hypergeometric functions

AbstractIn 1993 one of the authors formulated some conjectures on monotonicity of ratios for exponential series sections. These lead to a more general conjecture on monotonicity of ratios of Kummer hypergeometric functions, which remained open ever since. In this paper we prove some conjectures for Kummer hypergeometric functions and its further generalizations for Gauss and generalized hypergeometric functions. The results are also closely connected with Turán-type inequalities.

Analytical solution for slip flow and heat transfer due to a stretching sheet

AbstractAn analysis has been carried out to investigate the analytical solution to the flow and heat transfer characteristics of a viscous flow over a stretching sheet in the presence of second‐order slip in flow. The governing partial differential equations of flow and heat transfer are converted into non‐linear ordinary differential equations by using suitable similarity transformations. The exact solution of momentum equation is assumed in exponential form and analytical solutions of heat transfer for both PST and PHF cases are obtained by the power series method in terms of Kummer's hypergeometric function. The temperature profiles are drawn for different governing parameters. The numerical values of wall temperature gradient and wall temperature are compared with earlier numerical results which have a good agreement. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21044

Fisher information of special functions and second-order differential equations

We investigate a basic question of analytic information theory, namely, the evaluation of the Fisher information and the relative Fisher information with respect to a non-negative function, for the probability distributions obtained by squaring the special functions of mathematical physics which are solutions of second-order differential equations. We obtain explicit expressions for these information-theoretic properties via the expectation values of the coefficients of the differential equation. We illustrate our approach for various nonrelativistic D-dimensional wavefunctions and some special functions of physicomathematical interest. Emphasis is made in the Nikiforov–Uvarov hypergeometric-type functions, which include and generalize the Hermite functions and the Gauss and Kummer hypergeometric functions, among others.

The influence of prior knowledge on the expected performance of a classifier

In this paper, we study the probabilistic properties of pattern classifiers in discrete feature space. The principle of Bayesian averaging of recognition performance is used for this analysis. We consider two cases: (a) prior probabilities of classes are unknown, and (b) prior probabilities of classes are known. The misclassification probability is represented as a random value, for which the characteristic function (expressed via Kummer hypergeometric function) and absolute moments are analytically derived. For the case of unknown priors, an approximate formula for calculation of sufficient learning sample size is obtained. The comparison between the performances for two considered cases is made. As an example, we consider the problem of mutational hotspots classification in genetic sequences.

ASYMPTOTIC EXPANSIONS APPLIED TO F‐TEST CRITERIA

SummaryUsing asymptotic expansions of the Kummer hypergeometric function, the sequential. F‐test criterion is evaluated asymptotically in terms of the sample size. The continuation region inequalities for the test are inverted and expressed in terms of known test criteria. A rapidly converging algorithm for carrying out the sequential procedure is provided. This makes the F‐test easier for the practitioner to use. Almost sure finite termination of the sequential. F‐test is asserted by appealing to the continuation inequalities and a heuristic asymptotic expansion of the test criterion. Average stopping times of the sequential procedure for a variety of population means and population number configurations are tabulated. The computer symbolic manipulation program MAPLE was used to derive some formulae.

A generic model for long self-avoiding chain molecules

A generic model, which applies rigorously to finite chains in the absence of inter-segmental interactions, and to subchains of infinite chains with practically arbitrary interactions, furnishes a simple recurrence relation. Self-avoiding walks on the diamond lattice (SAW-D) form the paradigmatic example for polymer science. The generic model as a whole is solved (in terms of parameters) for configurational statistics, asymptotically (large number n of segments) and on stated plausible conjectures, by classical methods, i.e. without postulating a singularity of power law form. The appropriate generalisation of the power law form of scaling theory emerges very simply, e.g. in terms of Kummer's hypergeometric function. Extensive computations on the SAW-D model lead to two correction terms to the crude scaling form. In this way, some arguments in the literature on asymptotic theories can be settled. Several examples illustrate the danger of mistaking non-asymptotic experimental results for those desired in the asymptotic range. Thus, contrary to his own conclusions and those of Fleming (1979) Brun's data (1977) data for freely hinged hard-sphere chains are here reconciled with the 'universal' exponent gamma of Le Guillou and Zinn-Justin (1977). For the SAW-D model subject always to further refinements (which will never produce a final answer), the present experimental estimate for gamma is also shown to be about 1.2, in line with conjectural estimates from many forms of modern theory.