Balanced multi-wavelets in

The notion of -balancing was introduced a few years ago as a condition for the construction of orthonormal scaling function vectors and multi-wavelets to ensure the property of preservation/annihilation of scalar-valued discrete polynomial data of order (or degree ), when decomposed by the corresponding matrix-valued low-pass/high-pass filters. While this condition is indeed precise, to the best of our knowledge only the proof for is known. In addition, the formulation of the -balancing condition for is so prohibitively difficult to satisfy that only a very few examples for and vector dimension 2 have been constructed in the open literature. The objective of this paper is to derive various characterizations of the -balancing condition that include the polynomial preservation property as well as equivalent formulations that facilitate the development of methods for the construction purpose. These results are established in the general multivariate and bi-orthogonal settings for any .

     

Predicting nonlinear pseudorandom number generators

Let be a prime and let and be elements of the finite field of elements. The inversive congruential generator (ICG) is a sequence of pseudorandom numbers defined by the relation . We show that if sufficiently many of the most significant bits of several consecutive values of the ICG are given, one can recover the initial value (even in the case where the coefficients and are not known). We also obtain similar results for the quadratic congruential generator (QCG), , where . This suggests that for cryptographic applications ICG and QCG should be used with great care. Our results are somewhat similar to those known for the linear congruential generator (LCG), , but they apply only to much longer bit strings. We also estimate limits of some heuristic approaches, which still remain much weaker than those known for LCG.

     

Computing weight modular forms of level

For a prime we describe an algorithm for computing the Brandt matrices giving the action of the Hecke operators on the space of modular forms of weight and level . For we define a special Hecke stable subspace of which contains the space of modular forms with CM by the ring of integers of and we describe the calculation of the corresponding Brandt matrices.

     

A solution to certain polynomial equations with applications to nonlinear fitting

We present a combinatorial method for solving a certain system of polynomial equations of Vandermonde type in variables by reducing it to the problem of solving two special linear systems of size and rooting a single univariate polynomial of degree . Over , all solutions can be found with fixed precision using, up to polylogarithmic factors, bitwise operations in the worst case. Furthermore, if the data is well conditioned, then this can be reduced to bit operations, up to polylogarithmic factors. As an application, we show how this can be used to fit data to a complex exponential sum with terms in the same, nearly optimal, time.

     

A finite dimensional realization of the mollifier method for compact operator equations

We introduce and analyze a stable procedure for the approximation of where is the least residual norm solution of the minimal norm of the ill-posed equation , with compact operator between Hilbert spaces, and has some smoothness assumption. Our method is based on a finite number of singular values of and some finite rank operators. Our results are in a more general setting than the one considered by Rieder and Schuster (2000) and Nair and Lal (2003) with special reference to the mollifier method, and it is also applicable under fewer smoothness assumptions on .

     

Pointwise error estimates of the local discontinuous Galerkin method for a second order elliptic problem

In this paper we derive some pointwise error estimates for the local discontinuous Galerkin (LDG) method for solving second-order elliptic problems in (). Our results show that the pointwise errors of both the vector and scalar approximations of the LDG method are of the same order as those obtained in the norm except for a logarithmic factor when the piecewise linear functions are used in the finite element spaces. Moreover, due to the weighted norms in the bounds, these pointwise error estimates indicate that when at least piecewise quadratic polynomials are used in the finite element spaces, the errors at any point depend very weakly on the true solution and its derivatives in the regions far away from . These localized error estimates are similar to those obtained for the standard conforming finite element method.

     

On the nonexistence of -cycles for the problem

This article generalizes a proof of Steiner for the nonexistence of -cycles for the problem to a proof for the nonexistence of -cycles. A lower bound for the cycle length is derived by approximating the ratio between numbers in a cycle. An upper bound is found by applying a result of Laurent, Mignotte, and Nesterenko on linear forms in logarithms. Finally numerical calculation of convergents of shows that -cycles cannot exist.

     

Solutions of the congruence

To supplement existing data, solutions of are tabulated for primes with and . For , five new solutions 2^{32}$"> are presented. One of these, for , also satisfies the ``reverse' congruence . An effective procedure for searching for such ``double solutions' is described and applied to the range , . Previous to this, congruences are generally considered for any and fixed prime to see where the smallest prime solution occurs.

     

Five consecutive positive odd numbers, none of which can be expressed as a sum of two prime powers

In this paper, we prove that there is an arithmetic progression of positive odd numbers for each term of which none of five consecutive odd numbers and can be expressed in the form , where is a prime and are nonnegative integers.

     

Finding -strong pseudoprimes

Let be odd primes and . Put

Then we call the kernel, the triple the signature, and the height of , respectively. We call a -number if it is a Carmichael number with each prime factor . If is a -number and a strong pseudoprime to the bases for , we call a -spsp . Since -numbers have probability of error (the upper bound of that for the Rabin-Miller test), they often serve as the exact values or upper bounds of (the smallest strong pseudoprime to all the first prime bases). If we know the exact value of , we will have, for integers , a deterministic efficient primality testing algorithm which is easy to implement.

In this paper, we first describe an algorithm for finding -spsp(2)'s, to a given limit, with heights bounded. There are in total -spsp's with heights . We then give an overview of the 21978 - spsp(2)'s and tabulate of them, which are -spsp's to the first prime bases up to ; three numbers are spsp's to the first 11 prime bases up to 31. No -spsp's to the first prime bases with heights were found. We conjecture that there exist no -spsp's to the first prime bases with heights and so that

which was found by the author in an earlier paper. We give reasons to support the conjecture. The main idea of our method for finding those -spsp's is that we loop on candidates of signatures and kernels with heights bounded, subject those candidates of -spsp's and their prime factors to Miller's tests, and obtain the desired numbers. At last we speed our algorithm for finding larger -spsp's, say up to , with a given signature to more prime bases. Comparisons of effectiveness with Arnault's and our previous methods for finding -strong pseudoprimes to the first several prime bases are given.

     

Real zeros of Dedekind zeta functions of real quadratic fields

Let be a primitive, real and even Dirichlet character with conductor , and let be a positive real number. An old result of H. Davenport is that the cycle sums are all positive at and this has the immediate important consequence of the positivity of . We extend Davenport's idea to show that in fact for , 0$"> for all with so that one can deduce the positivity of by the nonnegativity of a finite sum for any . A simple algorithm then allows us to prove numerically that has no positive real zero for a conductor up to 200,000, extending the previous record of 986 due to Rosser more than 50 years ago. We also derive various estimates explicit in of the as well as the shifted cycle sums considered previously by Leu and Li for . These explicit estimates are all rather tight and may have independent interests.

     

More on the total number of prime factors of an odd perfect number

Let denote the sum of the positive divisors of . We say that is perfect if . Currently there are no known odd perfect numbers. It is known that if an odd perfect number exists, then it must be of the form , where are distinct primes and . Define the total number of prime factors of as . Sayers showed that . This was later extended by Iannucci and Sorli to show that . This paper extends these results to show that .

     

On the absolute Mahler measure of polynomials having all zeros in a sector. II

Let be an algebraic integer of degree , not or a root of unity, all of whose conjugates are confined to a sector . In the paper On the absolute Mahler measure of polynomials having all zeros in a sector, G. Rhin and C. Smyth compute the greatest lower bound of the absolute Mahler measure ( of , for belonging to nine subintervals of . In this paper, we improve the result to thirteen subintervals of and extend some existing subintervals.

     

Algorithms without accuracy saturation for evolution equations in Hilbert and Banach spaces

We consider the Cauchy problem for the first and the second order differential equations in Banach and Hilbert spaces with an operator coefficient depending on the parameter . We develop discretization methods with high parallelism level and without accuracy saturation; i.e., the accuracy adapts automatically to the smoothness of the solution. For analytical solutions the rate of convergence is exponential. These results can be viewed as a development of parallel approximations of the operator exponential and of the operator cosine family with a constant operator possessing exponential accuracy and based on the Sinc-quadrature approximations of the corresponding Dunford-Cauchy integral representations of solutions or the solution operators.

     

Recovering signals from inner products involving prolate spheroidals in the presence of jitter

The paper deals with recovering band- and energy-limited signals from a finite set of perturbed inner products involving the prolate spheroidal wavefunctions. The measurement noise (bounded by ) and jitter meant as perturbation of the ends of the integration interval (bounded by ) are considered. The upper and lower bounds on the radius of information are established. We show how the error of the best algorithms depends on and . We prove that jitter causes error of order , where is a bandwidth, which is similar to the error caused by jitter in the case of recovering signals from samples.

     

Some properties of the gamma and psi functions, with applications

In this paper, some monotoneity and concavity properties of the gamma, beta and psi functions are obtained, from which several asymptotically sharp inequalities follow. Applying these properties, the authors improve some well-known results for the volume of the unit ball , the surface area of the unit sphere , and some related constants.

     

Even moments of generalized Rudin-Shapiro polynomials

We know from Littlewood (1968) that the moments of order of the classical Rudin-Shapiro polynomials satisfy a linear recurrence of degree . In a previous article, we developed a new approach, which enables us to compute exactly all the moments of even order for . We were also able to check a conjecture on the asymptotic behavior of , namely , where , for even and . Now for every integer there exists a sequence of generalized Rudin-Shapiro polynomials, denoted by . In this paper, we extend our earlier method to these polynomials. In particular, the moments have been completely determined for and , for and and for and . For higher values of and , we formulate a natural conjecture, which implies that , where is an explicit constant.

     

Solving quadratic equations using reduced unimodular quadratic forms

Let be an symmetric matrix with integral entries and with , but not necesarily positive definite. We describe a generalized LLL algorithm to reduce this quadratic form. This algorithm either reduces the quadratic form or stops with some isotropic vector. It is proved to run in polynomial time. We also describe an algorithm for the minimization of a ternary quadratic form: when a quadratic equation is solvable over , a solution can be deduced from another quadratic equation of determinant . The combination of these algorithms allows us to solve efficiently any general ternary quadratic equation over , and this gives a polynomial time algorithm (as soon as the factorization of the determinant of is known).

     

Error estimates for semi-discrete gauge methods for the Navier-Stokes equations

The gauge formulation of the Navier-Stokes equations for incompressible fluids is a new projection method. It splits the velocity in terms of auxiliary (nonphysical) variables and and replaces the momentum equation by a heat-like equation for and the incompressibility constraint by a diffusion equation for . This paper studies two time-discrete algorithms based on this splitting and the backward Euler method for with explicit boundary conditions and shows their stability and rates of convergence for both velocity and pressure. The analyses are variational and hinge on realistic regularity requirements on the exact solution and data. Both Neumann and Dirichlet boundary conditions are, in principle, admissible for but a compatibility restriction for the latter is uncovered which limits its applicability.