arXiv subjects

Masataka Kanki

Publications and source records attributed to Masataka Kanki.

At least 19 recordsLinked to original sources

arXiv2020

Coprimeness-preserving discrete KdV type equation on an arbitrary dimensional lattice

We introduce an equation defined on a multi-dimensional lattice, which can be considered as an extension to the coprimeness-preserving discrete KdV like equation in our previous paper. The equation is also interpreted as a higher-dimensional analogue of the Hietarinta-Viallet equation, which is famous for its singularity confining property while having an exponential degree growth. As the main theorem we prove the Laurent and the irreducibility properties of the equation in its "tau-function" form. From the theorem the coprimeness of the equation follows. In Appendix we review the coprimeness-preserving discrete KdV like equation whichis a base equation for our main system and prove the properties such as the coprimeness.

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arXiv2019

Algebraic entropy of a multi-term recurrence of the Hietarinta-Viallet type

We introduce a family of extensions of the Hietarinta-Viallet equation to a multi-term recurrence relation via a reduction from the coprimeness-preserving extension to the discrete KdV equation. The recurrence satisfies the irreducibility and the coprimeness property although it is nonintegrable in terms of an exponential degree growth. We derive the algebraic entropy of the recurrence by an elementary method of calculating the degree growth. The result includes the entropy of the original Hietarinta-Viallet equation.

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arXiv2018

On the Coprimeness Property of Discrete Systems without the Irreducibility Condition

In this article we investigate the coprimeness properties of one and two-dimensional discrete equations, in a situation where the equations are decomposable into several factors of polynomials. After experimenting on a simple equation, we shall focus on some higher power extensions of the Somos-4 equation and the (1-dimensional) discrete Toda equation. Our previous results are that all of the equations satisfy the irreducibility and the coprimeness properties if the r.h.s. is not factorizable. In this paper we shall prove that the coprimeness property still holds for all of these equations even if the r.h.s. is factorizable, although the irreducibility property is no longer satisfied.

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arXiv2018

Toda type equations over multi-dimensional lattices

We introduce a class of recursions defined over the $d$-dimensional integer lattice. The discrete equations we study are interpreted as higher dimensional extensions to the discrete Toda lattice equation. We shall prove that the equations satisfy the coprimeness property, which is one of integrability detectors analogous to the singularity confinement test. While the degree of their iterates grows exponentially, their singularities exhibit a nature similar to that of integrable systems in terms of the coprimeness property. We also prove that the equations can be expressed as mutations of a seed in the sense of the Laurent phenomenon algebra.

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arXiv2018

Nonlinear forms of coprimeness preserving extensions to the Somos-$4$ recurrence and the two-dimensional Toda lattice equation --investigation into their extended Laurent properties--

Coprimeness property was introduced to study the singularity structure of discrete dynamical systems. In this paper we shall extend the coprimeness property and the Laurent property to further investigate discrete equations with complicated pattern of singularities. As examples we study extensions to the Somos-$4$ recurrence and the two-dimensional discrete Toda equation. By considering their non-autonomous polynomial forms, we prove that their tau function analogues possess the extended Laurent property with respect to their initial variables and some extra factors related to the non-autonomous terms. Using this Laurent property, we prove that these equations satisfy the extended coprimeness property. This coprimeness property reflects the singularities that trivially arise from the equations.

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arXiv2018

A two dimensional lattice equation as an extension of the Heideman-Hogan recurrence

We consider a two dimensional extension of the so-called linearizable mappings. In particular, we start from the Heideman-Hogan recurrence, which is known as one of the linearizable Somos-like recurrences, and introduce one of its two dimensional extensions. The two dimensional lattice equation we present is linearizable in both directions, and has the Laurent and the coprimeness properties. Moreover, its reduction produces a generalized family of the Heideman-Hogan recurrence. Higher order examples of two dimensional linearizable lattice equations related to the Dana-Scott recurrence are also discussed.

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arXiv2016

Coprimeness-preserving non-integrable extension to the two-dimensional discrete Toda lattice equation

We introduce a so-called `coprimeness-preserving non-integrable' extension (another terminology is `quasi-integrable' extension) to the two-dimensional Toda lattice equation. We believe that this equation is the first example of such discrete equation defined over a three-dimensional lattice. We prove that all the iterates of the equation are irreducible Laurent polynomials of the initial data and that every pair of two iterates is co-prime, which indicate confined singularities of the equation. By reducing the equation to two- or one-dimensional lattices, we obtain coprimeness-preserving non-integrable extensions to the one-dimensional Toda lattice equation and the Somos-4 recurrence.

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arXiv2016

Graphs emerging from the solutions to the periodic discrete Toda equation over finite fields

The periodic discrete Toda equation defined over finite fields has been studied. We obtained the finite graph structures constructed by the network of states where edges denote possible time evolutions. We simplify the graphs by introducing a equivalence class of cyclic permutations to the initial values. We proved that the graphs are bi-directional and that they are composed of several arrays of complete graphs connected at one of their vertices.

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arXiv2016

Singularity confinement and chaos in two-dimensional discrete systems

We present a quasi-integrable two-dimensional lattice equation: i.e., a partial difference equation which satisfies a criterion of integrability, singularity confinement, although it has a chaotic aspect in the sense that the degrees of its iterates exhibit exponential growth. By systematic reduction to one-dimensional systems, it gives a hierarchy of ordinary difference equations with confined singularities, but with positive algebraic entropy including a generalized form of the Hietarinta-Viallet mapping. We believe that this is the first example of such quasi-integrable equations defined over a two-dimensional lattice.

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arXiv2015

Algebraic entropy of an extended Hietarinta-Viallet equation

We introduce a series of discrete mappings, which is considered to be an extension of the Hietarinta-Viallet mapping with one parameter. We obtain the algebraic entropy for this mapping by obtaining the recurrence relation for the degrees of the iterated mapping. For some parameter values the mapping has a confined singularity, in which case the mapping is equivalent to a recurrence relation between irreducible polynomials. For other parameter values, the mapping does not pass the singularity confinement test. The properties of irreducibility and co-primeness of the terms play crucial roles in the discussion.

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arXiv2015

Integrability criterion in terms of coprime property for the discrete Toda equation

We reformulate the singularity confinement of the discrete Toda equation. We prove the co-primeness property, which has been introduced in our previous paper (arXiv:1311.0060) as one of the integrability criteria, for the discrete Toda equation. We study three types of boundary conditions (semi-infinite, molecule, periodic) for the discrete Toda equation, and prove that the same co-primeness property holds for all the types of boundaries. (v2: typos corrected, final version to appear in J. Math. Phys.)

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arXiv2014

Singularities of the discrete KdV equation and the Laurent property

We study the distribution of singularities for partial difference equations, in particular, the bilinear and nonlinear form of the discrete version of the Korteweg-de Vries (dKdV) equation. By the Laurent property, the irreducibility, and the co-primeness of the terms of the bilinear dKdV equation, we clarify the relationship of these properties with the appearance of zeros in the time evolution. The results are applied to the nonlinear dKdV equation and we formulate the famous integrability criterion (singularity confinement test) for nonlinear partial difference equations with respect to the co-primeness of the terms. (v2,v3,v4: minor revisions have been made)

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arXiv2014

The redemption of singularity confinement

We present a novel way to apply the singularity confinement property as a discrete integrability criterion. We shall use what we call a full deautonomisation approach, which consists in treating the free parameters in the mapping as functions of the independent variable, applied to a mapping complemented with terms that are absent in the original mapping but which do not change the singularity structure. We shall show, on a host of examples including the well-known mapping of Hietarinta-Viallet, that our approach offers a way to compute the algebraic entropy for these mappings exactly, thereby allowing one to distinguish between the integrable and non-integrable cases even when both have confined singularities.

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arXiv2014

Studies on the discrete integrable equations over finite fields

Discrete dynamical systems over finite fields are investigated and their integrability is discussed. In particular, the discrete Painlevé equations and the discrete KdV equation are defined over finite fields and their special solutions are obtained. Their investigation over the finite fields has not been done thoroughly, partly because of the indeterminacies that appear in defining the equations. In this paper we introduce two methods to well-define the equations over the finite fields and apply the methods to several classes of discrete integrable equations. One method is to extend the space of initial conditions through blowing-up at the singular points. In case of discrete Painlevé equations, we prove that an finite field analog of the Sakai theory can be applied to construct the space of initial conditions. The other method is to define the equations over the field of $p$-adic numbers and then reduce them to the finite fields. The mapping whose time evolutions commute with the reduction is said to have a `good reduction'. We generalize good reduction in order to be applied to integrable mappings. The generalized good reduction is formulated as `almost good reduction' and is proved to be a $p$-adic analog of the singularity confinement test. (*Note that this paper is intended for the author's thesis and it draws from several of our already published papers. Also note that several minor modifications have been made from the original thesis.)

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arXiv2014

Irreducibility and co-primeness as an integrability criterion for discrete equations

We study the Laurent property, the irreducibility and co-primeness of discrete integrable and non-integrable equations. First we study a discrete integrable equation related to the Somos-4 sequence, and also a non-integrable equation as a comparison. We prove that the conditions of irreducibility and co-primeness hold only in the integrable case. Next, we generalize our previous results on the singularities of the discrete Korteweg-de Vries (dKdV) equation. In our previous paper (arXiv:1311.0060), we described the singularity confinement test (one of the integrability criteria) using the Laurent property, and the irreducibility, and co-primeness of the terms in the bilinear dKdV equation, in which we only considered simplified boundary conditions. This restriction was needed to obtain simple (monomial) relations between the bilinear form and the nonlinear form of the dKdV equation. In this paper, we prove the co-primeness of the terms in the nonlinear dKdV equation for general initial conditions and boundary conditions, by using the localization of Laurent rings and the interchange of the axes. We assert that co-primeness of the terms can be used as a new integrability criterion, which is a mathematical re-interpretation of the confinement of singularities in the case of discrete equations. v2, v3: minor revisions

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arXiv2014

Discrete Painleve equations and discrete KdV equation over finite fields

We investigate some of the discrete Painleve equations (dPII, qPI and qPII) and the discrete KdV equation over finite fields. The first part concerns the discrete Painleve equations. We review some of the ideas introduced in our previous papers and give some detailed discussions. We first show that they are well defined by extending the domain according to the theory of the space of initial conditions. We then extend them to the field of p-adic numbers and observe that they have a property that is called an `almost good reduction' of dynamical systems over finite fields. We can use this property, which can be interpreted as an arithmetic analogue of singularity confinement, to avoid the indeterminacy of the equations over finite fields and to obtain special solutions from those defined originally over fields of characteristic zero. In the second part we study the discrete KdV equation. We review the previous discussions and present a way to resolve the indeterminacy of the equation by treating it over a field of rational functions instead of the finite field itself. Explicit forms of soliton solutions and their periods over finite fields are obtained. Note: This is a review article on the recent developments in the theory of discrete integrable equations over finite fields based on arXiv:1201.5429, arXiv:1206.4456, arXiv:1209.0223. This article is published as the proceedings of the domestic conference "The breadth and depth of nonlinear discrete integrable systems" in RIMS, Kyoto University, Japan, on August 2012.

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arXiv2013

The space of initial conditions and the property of an almost good reduction in discrete Painleve II equations over finite fields

Discrete versions of the Painleve equations (dPII and qPII) over finite fields are studied. We first show that they are well defined by extending the domain according to the theory of the space of initial conditions, taking the dPII equation as an example. Then we define them over the field of p-adic numbers and see that they have a property that is similar to the good reduction of dynamical systems modulo a prime. This property is called 'almost good reduction'. We study the q-discrete analogue of the Painleve II equation in this paper, following the method in our previous work (arXiv: 1206.4456), in which the discrete Painleve II equation has been treated. We can consider almost good reduction as an arithmetic analogue of the singularity confinement test. We can also obtain special solutions over finite fields from those defined over fields of characteristic zero. (v2: excluded the review of arXiv: 1206.4456) (v3: several typos are corrected) (v4: final version to appear in J. Nonlin. Math. Phys.)

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arXiv2013

Integrability of Discrete Equations Modulo a Prime

We apply the 'almost good reduction' (AGR) criterion, which has been introduced in our previous (arXiv:1206.4456 and arXiv:1209.0223), to several classes of discrete integrable equations. We verify our conjecture that AGR plays the same role for maps of the plane define over simple finite fields as the notion of the singularity confinement does. We first prove that q-discrete analogues of the Painlevé III and IV equations have AGR. We next prove that the Hietarinta-Viallet equation, a non-integrable chaotic system also has AGR.

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