Corrigenda and addition to ``Computer verification of the Ankeny-Artin-Chowla conjecture for all primes less than '

An error in the program for verifying the Ankeny-Artin-Chowla (AAC) conjecture is reported. As a result, in the case of primes which are , the AAC conjecture has been verified using a different multiple of the regulator of the quadratic field than was meant. However, since any multiple of this regulator is suitable for this purpose, provided that it is smaller than , the main result that the AAC conjecture is true for all the primes which are , remains valid.

As an addition, we have verified the AAC conjecture for all the primes between and , with the corrected program.

     

New quadratic polynomials with high densities of prime values

Hardy and Littlewood's Conjecture F implies that the asymptotic density of prime values of the polynomials , is related to the discriminant of via a quantity The larger is, the higher the asymptotic density of prime values for any quadratic polynomial of discriminant . A technique of Bach allows one to estimate accurately for any , given the class number of the imaginary quadratic order with discriminant , and for any 0$"> given the class number and regulator of the real quadratic order with discriminant . The Manitoba Scalable Sieve Unit (MSSU) has shown us how to rapidly generate many discriminants for which is potentially large, and new methods for evaluating class numbers and regulators of quadratic orders allow us to compute accurate estimates of efficiently, even for values of with as many as decimal digits. Using these methods, we were able to find a number of discriminants for which, under the assumption of the Extended Riemann Hypothesis, is larger than any previously known examples.

     

A convergence and stability study of the iterated Lubkin transformation and the -algorithm

In this paper we analyze the convergence and stability of the iterated Lubkin transformation and the -algorithm as these are being applied to sequences whose members behave like as , where and are complex scalars and is a nonnegative integer. We study the three different cases in which (i) , , and (logarithmic sequences), (ii) and (linear sequences), and (iii) (factorial sequences). We show that both methods accelerate the convergence of all three types of sequences. We show also that both methods are stable on linear and factorial sequences, and they are unstable on logarithmic sequences. On the basis of this analysis we propose ways of improving accuracy and stability in problematic cases. Finally, we provide a comparison of these results with analogous results corresponding to the Levin -transformation.

     

Modular curves of genus 2

We prove that there are exactly genus two curves defined over such that there exists a nonconstant morphism defined over and the jacobian of is -isogenous to the abelian variety attached by Shimura to a newform . We determine the corresponding newforms and present equations for all these curves.

     

A fast algorithm for testing reducibility of trinomials mod 2 and some new primitive trinomials of degree 3021377

The standard algorithm for testing reducibility of a trinomial of prime degree over requires bits of memory. We describe a new algorithm which requires only bits of memory and significantly fewer memory references and bit-operations than the standard algorithm.

If is a Mersenne prime, then an irreducible trinomial of degree is necessarily primitive. We give primitive trinomials for the Mersenne exponents , , and . The results for extend and correct some computations of Kumada et al. The two results for are primitive trinomials of the highest known degree.

     

Nontrivial Galois module structure of cyclotomic fields

We say a tame Galois field extension with Galois group has trivial Galois module structure if the rings of integers have the property that is a free -module. The work of Greither, Replogle, Rubin, and Srivastav shows that for each algebraic number field other than the rational numbers there will exist infinitely many primes so that for each there is a tame Galois field extension of degree so that has nontrivial Galois module structure. However, the proof does not directly yield specific primes for a given algebraic number field For any cyclotomic field we find an explicit so that there is a tame degree extension with nontrivial Galois module structure.

     

Linear quintuple-product identities

In the first part of this paper, series and product representations of four single-variable triple products , , , and four single-variable quintuple products , , , are defined. Reduced forms and reduction formulas for these eight functions are given, along with formulas which connect them. The second part of the paper contains a systematic computer search for linear trinomial identities. The complete set of such families is found to consist of two 2-parameter families, which are proved using the formulas in the first part of the paper.

     

Minimality and other properties of the width- nonadjacent form

Let be an integer and let be the set of integers that includes zero and the odd integers with absolute value less than . Every integer can be represented as a finite sum of the form , with , such that of any consecutive 's at most one is nonzero. Such representations are called width- nonadjacent forms (-NAFs). When these representations use the digits and coincide with the well-known nonadjacent forms. Width- nonadjacent forms are useful in efficiently implementing elliptic curve arithmetic for cryptographic applications. We provide some new results on the -NAF. We show that -NAFs have a minimal number of nonzero digits and we also give a new characterization of the -NAF in terms of a (right-to-left) lexicographical ordering. We also generalize a result on -NAFs and show that any base 2 representation of an integer, with digits in , that has a minimal number of nonzero digits is at most one digit longer than its binary representation.

     

Lower bounds for the total stopping time of iterates

The total stopping time of a positive integer is the minimal number of iterates of the function needed to reach the value , and is if no iterate of reaches . It is shown that there are infinitely many positive integers having a finite total stopping time such that 6.14316 \log n.$"> The proof involves a search of trees to depth 60, A heuristic argument suggests that for any constant , a search of all trees to sufficient depth could produce a proof that there are infinitely many such that \gamma\log n.$">It would require a very large computation to search trees to a sufficient depth to produce a proof that the expected behavior of a ``random' iterate, which is occurs infinitely often.

     

Newman polynomials with prescribed vanishing and integer sets with distinct subset sums

We study the problem of determining the minimal degree of a polynomial that has all coefficients in and a zero of multiplicity at . We show that a greedy solution is optimal precisely when , mirroring a result of Boyd on polynomials with coefficients. We then examine polynomials of the form , where is a set of positive odd integers with distinct subset sums, and we develop algorithms to determine the minimal degree of such a polynomial. We determine that satisfies inequalities of the form . Last, we consider the related problem of finding a set of positive integers with distinct subset sums and minimal largest element and show that the Conway-Guy sequence yields the optimal solution for , extending some computations of Lunnon.

     

Solving norm equations in relative number fields using -units

In this paper, we are interested in solving the so-called norm equation , where is a given arbitrary extension of number fields and a given algebraic number of . By considering -units and relative class groups, we show that if there exists at least one solution (in , but not necessarily in ), then there exists a solution for which we can describe precisely its prime ideal factorization. In fact, we prove that under some explicit conditions, the -units that are norms are norms of -units. This allows us to limit the search for rational solutions to a finite number of tests, and we give the corresponding algorithm. When is an algebraic integer, we also study the existence of an integral solution, and we can adapt the algorithm to this case.

     

On the modular curves

Let denote an elliptic curve over and the modular curve classifying the elliptic curves over such that the representations of in the 7-torsion points of and of are symplectically isomorphic. In case is given by a Weierstraß equation such that the invariant is a square, we exhibit here nontrivial points of . From this we deduce an infinite family of curves for which has at least four nontrivial points.

     

On the convergence of certain Gauss-type quadrature formulas for unbounded intervals

We consider the convergence of Gauss-type quadrature formulas for the integral , where is a weight function on the half line . The -point Gauss-type quadrature formulas are constructed such that they are exact in the set of Laurent polynomials }, where is a sequence of integers satisfying and . It is proved that under certain Carleman-type conditions for the weight and when or goes to , then convergence holds for all functions for which is integrable on . Some numerical experiments compare the convergence of these quadrature formulas with the convergence of the classical Gauss quadrature formulas for the half line.

     

About the sharpness of the stability estimates in the Kreiss matrix theorem

One of the conditions in the Kreiss matrix theorem involves the resolvent of the matrices under consideration. This so-called resolvent condition is known to imply, for all , the upper bounds and . Here is the spectral norm, is the constant occurring in the resolvent condition, and the order of is equal to .

It is a long-standing problem whether these upper bounds can be sharpened, for all fixed 1$">, to bounds in which the right-hand members grow much slower than linearly with and with , respectively. In this paper it is shown that such a sharpening is impossible. The following result is proved: for each 0$">, there are fixed values 0, K>1$"> and a sequence of matrices , satisfying the resolvent condition, such that for .

The result proved in this paper is also relevant to matrices whose -pseudospectra lie at a distance not exceeding from the unit disk for all 0$">.

     

On the step-by-step construction of quasi-Monte Carlo integration rules that achieve strong tractability error bounds in weighted Sobolev spaces

We develop and justify an algorithm for the construction of quasi-Monte Carlo (QMC) rules for integration in weighted Sobolev spaces; the rules so constructed are shifted rank-1 lattice rules. The parameters characterising the shifted lattice rule are found ``component-by-component': the ()-th component of the generator vector and the shift are obtained by successive -dimensional searches, with the previous components kept unchanged. The rules constructed in this way are shown to achieve a strong tractability error bound in weighted Sobolev spaces. A search for -point rules with prime and all dimensions 1 to requires a total cost of operations. This may be reduced to operations at the expense of storage. Numerical values of parameters and worst-case errors are given for dimensions up to 40 and up to a few thousand. The worst-case errors for these rules are found to be much smaller than the theoretical bounds.

     

Enhanced accuracy by post-processing for finite element methods for hyperbolic equations

We consider the enhancement of accuracy, by means of a simple post-processing technique, for finite element approximations to transient hyperbolic equations. The post-processing is a convolution with a kernel whose support has measure of order one in the case of arbitrary unstructured meshes; if the mesh is locally translation invariant, the support of the kernel is a cube whose edges are of size of the order of only. For example, when polynomials of degree are used in the discontinuous Galerkin (DG) method, and the exact solution is globally smooth, the DG method is of order in the -norm, whereas the post-processed approximation is of order ; if the exact solution is in only, in which case no order of convergence is available for the DG method, the post-processed approximation converges with order in , where is a subdomain over which the exact solution is smooth. Numerical results displaying the sharpness of the estimates are presented.

     

Upper bounds for the prime divisors of Wendt's determinant

Let be an even integer, . The resultant of the polynomials and is known as Wendt's determinant of order . We prove that among the prime divisors of only those which divide or can be larger than , where and is the th Lucas number, except when and . Using this estimate we derive criteria for the nonsolvability of Fermat's congruence.

     

Class numbers of real cyclotomic fields of prime conductor

The class numbers of the real cyclotomic fields are notoriously hard to compute. Indeed, the number is not known for a single prime . In this paper we present a table of the orders of certain subgroups of the class groups of the real cyclotomic fields for the primes . It is quite likely that these subgroups are in fact equal to the class groups themselves, but there is at present no hope of proving this rigorously. In the last section of the paper we argue --on the basis of the Cohen-Lenstra heuristics-- that the probability that our table is actually a table of class numbers , is at least .

     

Random Fibonacci sequences and the number

For the familiar Fibonacci sequence (defined by , and for ), increases exponentially with at a rate given by the golden ratio . But for a simple modification with both additions and subtractions - the random Fibonacci sequences defined by , and for , , where each sign is independent and either or - with probability - it is not even obvious if should increase with . Our main result is that

with probability . Finding the number involves the theory of random matrix products, Stern-Brocot division of the real line, a fractal measure, a computer calculation, and a rounding error analysis to validate the computer calculation.

     

A superconvergent LDG-hybridizable Galerkin method for second-order elliptic problems

We identify and study an LDG-hybridizable Galerkin method, which is not an LDG method, for second-order elliptic problems in several space dimensions with remarkable convergence properties. Unlike all other known discontinuous Galerkin methods using polynomials of degree for both the potential as well as the flux, the order of convergence in of both unknowns is . Moreover, both the approximate potential as well as its numerical trace superconverge in -like norms, to suitably chosen projections of the potential, with order . This allows the application of element-by-element postprocessing of the approximate solution which provides an approximation of the potential converging with order in . The method can be thought to be in between the hybridized version of the Raviart-Thomas and that of the Brezzi-Douglas-Marini mixed methods.