arXiv subjects

Greg Martin

Publications and source records attributed to Greg Martin.

At least 73 records · Page 4Linked to original sources

arXiv2006

The Symmetric Subset Problem in Continuous Ramsey Theory

A symmetric subset of the reals is one that remains invariant under some reflection z --> c-z. We consider, for any 0 < x <= 1, the largest real number D(x) such that every subset of $[0,1]$ with measure greater than x contains a symmetric subset with measure D(x). In this paper we establish upper and lower bounds for D(x) of the same order of magnitude: for example, we prove that D(x) = 2x - 1 for 11/16 <= x <= 1 and that 0.59 x^2 < D(x) < 0.8 x^2 for 0 < x <= 11/16. This continuous problem is intimately connected with a corresponding discrete problem. A set S of integers is called a B*[g] set if for any given m there are at most g ordered pairs (s_1,s_2) \in S \times S with s_1+s_2 = m; in the case g=2, these are better known as Sidon sets. Our lower bound on D(x) implies that every B*[g] set contained in \{1,2,...,n\} has cardinality less than 1.30036 \sqrt{gn}. This improves a result of Green for g >= 30. Conversely, we use a probabilistic construction of B*[g] sets to establish an upper bound on D(x) for small x.

math.CO↗

arXiv2006

Simultaneous inequalities among values of the Euler phi-function

This paper concerns the values of the Euler phi-function evaluated simultaneously on k arithmetic progressions a_1 n + b_1, a_2 n + b_2, ..., a_k n + b_k. Assuming the necessary condition that no two of the polynomials a_i x + b_i are constant multiples of each other, we show that there are infinitely many integers n for which phi(a_1 n + b_1) > phi(a_2 n + b_2) > ... > phi(a_k n + b_k). In particular, there exist infinitely many strings of k consecutive integers whose phi-values are arranged from largest to smallest in any prescribed manner. Also, under the necessary condition ad \ne bc, any inequality of the form phi(an+b) < phi(cn+d) infinitely often has k consecutive solutions. In fact, we prove that the sets of solutions to these inequalities have positive lower density.

math.NT↗

arXiv2006

A simple polynomial for a simple transposition

In this note, we review some facts about polynomials representing functions modulo primes p. In addition we prove that the polynomial f(x) = x^{p-2} + x^{p-3} + ... + x^3 + x^2 + 2x + 1 represents the transposition (0 1) modulo p, that is, f(0) \equiv 1 (mod p), f(1) \equiv 0 (mod p), and f(a) \equiv a (mod p) for all 2 \le a \le p-1.

math.NT↗

arXiv2005

Constructions of Generalized Sidon Sets

We give explicit constructions of sets S with the property that for each integer k, there are at most g solutions to k=s_1+s_2, s_i\in S; such sets are called Sidon sets if g=2 and generalized Sidon sets if g\ge 3. We extend to generalized Sidon sets the Sidon-set constructions of Singer, Bose, and Ruzsa. We also further optimize Koulantzakis' idea of interleaving several copies of a Sidon set, extending the improvements of Cilleruelo & Ruzsa & Trujillo, Jia, and Habsieger & Plagne. The resulting constructions yield the largest known generalized Sidon sets in virtually all cases.

math.NT↗

arXiv2004

Prime Number Races

This is a survey article on prime number races. Chebyshev noticed in the first half of the nineteenth century that for any given value of x, there always seem to be more primes of the form 4n+3 less than x then there are of the form 4n+1. Similar observations have been made with primes of the form 3n+2 and 3n+1, with primes of the form 10n+3/10n+7 and 10n+1/10n+9, and many others besides. More generally, one can consider primes of the form qn+a, qn+b, qn+c, >... for our favorite constants q, a, b, c, ... and try to figure out which forms are "preferred" over the others. In this paper, we describe these phenomena in greater detail and explain the efforts that have been made at understanding them.

math.NT↗

arXiv2004

The iterated Carmichael λ-function and the number of cycles of the power generator

Iteration of the modular l-th power function f(x) = x^l (mod n) provides a common pseudorandom number generator (known as the Blum-Blum-Shub generator when l=2). The period of this pseudorandom number generator is closely related to λ(λ(n)), where λ(n) denotes Carmichael's function, namely the maximal multiplicative order of any integer modulo n. In this paper, we show that for almost all n, the size of λ(λ(n)) is n/exp((1+o(1))(log log n)^2 log log log n). We conjecture an analogous formula for the k-th iterate of λ. We deduce that for almost all n, the psuedorandom number generator described above has at least exp((1+o(1))(log log n)^2 log log log n) disjoint cycles. In addition, we show that this expression is accurate for almost all n under the assumption of the Generalized Riemann Hypothesis for Kummerian fields. We also consider the number of iterations of λit takes to reduce an integer n to 1, proving that this number is less than (1+o(1))(log log n)/log 2 infinitely often and speculating that log log n is the true order of magnitude almost always.

math.NT↗

arXiv2003

Dimensions of the Spaces of Cusp Forms and Newforms on Gamma_0(N) and Gamma_1(N)

A formula for the dimension of the space of cuspidal modular forms on $Γ_0(N)$ of weight $k$ ($k\ge2$ even) has been known for several decades. More recent but still well-known is the Atkin-Lehner decomposition of this space of cusp forms into subspaces corresponding to newforms on $Γ_0(d)$ of weight $k$, as $d$ runs over the divisors of $N$. A recursive algorithm for computing the dimensions of these spaces of newforms follows from the combination of these two results, but it would be desirable to have a formula in closed form for these dimensions. In this paper we establish such a closed-form formula, not only for these dimensions, but also for the corresponding dimensions of spaces of newforms on $Γ_1(N)$ of weight $k$ ($k\ge2$). This formula is much more amenable to analysis and to computation. For example, we derive asymptotically sharp upper and lower bounds for these dimensions, and we compute their average orders; even for the dimensions of spaces of cusp forms, these results are new. We also establish sharp inequalities for the special case of weight-2 newforms on $Γ_0(N)$, and we report on extensive computations of these dimensions: we find the complete list of all $N$ such that the dimension of the space of weight-2 newforms on $Γ_0(N)$ is less than or equal to 100 (previous such results had only gone up to dimension 3).

math.NT↗

arXiv2002

Continuous Ramsey Theory and Sidon Sets

A symmetric subset of the reals is one that remains invariant under some reflection x --> c-x. Given 0 < x < 1, there exists a real number D(x) with the following property: if 0 < d < D(x), then every subset of [0,1] with measure x contains a symmetric subset with measure d, while if d > D(x), then there exists a subset of [0,1] with measure x that does not contain a symmetric subset with measure d. In this paper we establish upper and lower bounds for D(x) of the same order of magnitude: for example, we prove that D(x) = 2x - 1 for 11/16 < x < 1 and that 0.59 x^2 < D(x) < 0.8 x^2 for 0 < x < 11/16. This continuous problem is intimately connected with a corresponding discrete problem. A set S of integers is called a B*[g] set if for any given m there are at most g ordered pairs (s_1,s_2) \in S \times S with s_1+s_2=m; in the case g=2, these are better known as Sidon sets. We also establish upper and lower bounds of the same order of magnitude for the maximal possible size of a B*[g] set contained in {1,...,n}, which we denote by R(g,n). For example, we prove that R(g,n) < 1.31 \sqrt{gn} for all n > g > 1, while R(g,n) > 0.79 \sqrt{gn} for sufficiently large integers g and n. These two problems are so interconnected that both continuous and discrete tools can be applied to each problem with surprising effectiveness. The harmonic analysis methods and inequalities among various L^p norms we use to derive lower bounds for D(x) also provide uniform upper bounds for R(g,n), while the techniques from combinatorial and probabilistic number theory that we employ to obtain constructions of large B*[g] sets yield strong upper bounds for D(x).

math.NT↗

arXiv2002

Lower Bounds for the Number of Smooth Values of a Polynomial

We investigate the problem of showing that the values of a given polynomial are smooth (i.e., have no large prime factors) a positive proportion of the time. Although some results exist that bound the number of smooth values of a polynomial from above, a corresponding lower bound of the correct order of magnitude has hitherto been established only in a few special cases. The purpose of this paper is to provide such a lower bound for an arbitrary polynomial. Various generalizations to subsets of the set of values taken by a polynomial are also obtained.

math.NT↗

arXiv2002

The Unreasonable Effectualness of Continued Function Expansions

Many generalizations of continued fractions, where the reciprocal function has been replaced by a more general function, have been studied, and it is often asked whether such generalized expansions can have nice properties. For instance, we might ask that algebraic numbers of a given degree have periodic expansions, just as quadratic irrationals have periodic continued fractions; or we might ask that familiar transcendental constants such as $e$ or $π$ have periodic or terminating expansions. In this paper, we show that there exist such generalized continued function expansions with essentially any desired behavior.

math.NT↗

arXiv2002

The Limiting Curve of Jarnik's Polygons

In 1925, Jarnik defined a sequence of convex polygons for use in constructing curves containing many lattice points relative to their curvatures. Properly scaled, these polygons converge to a certain limiting curve. In this paper we identify this limiting curve precisely, showing that it consists piecewise of arcs of parabolas, and we discuss the analogous problem for sequences of polygons arising from generalizations of Jarnik's construction.

math.NT↗

arXiv2000

Absolutely Abnormal Numbers

Despite the fact that almost all real numbers are absolutely normal---that is, the digits in their expansions to any base occur in all possible configurations with the expected frequency---not one specific example of an absolutely normal number is known. In this note we investigate the opposite extreme, numbers that are normal to no base whatsoever, and we succeed in writing down explicitly such a number.

math.NT↗

arXiv2000

Asymmetries in the Shanks-Renyi Prime Number Race

It has been well-observed that an inequality of the type $π(x;q,a) > π(x;q,b)$ is more likely to hold if $a$ is a non-square modulo $q$ and $b$ is a square modulo $q$ (the so-called ``Chebyshev Bias''). For instance, each of $π(x;8,3)$, $π(x;8,5)$, and $π(x;8,7)$ tends to be somewhat larger than $π(x;8,1)$. However, it has come to light that the tendencies of these three $π(x;8,a)$ to dominate $π(x;8,1)$ have different strengths. A related phenomenon is that the six possible inequalities of the form $π(x;8,a_1) > π(x;8,a_2) > π(x;8,a_3)$ with $\{a_1,a_2,a_3\}=\{3,5,7\}$ are not all equally likely---some orderings are preferred over others. In this paper we discuss these phenomena, focusing on the moduli $q=8$ and $q=12$, and we explain why the observed asymmetries (as opposed to other possible asymmetries) occur.

math.NT↗

arXiv2000

An Asymptotic Formula for the Number of Smooth Values of a Polynomial

Although we expect to find many smooth numbers (i.e., numbers with no large prime factors) among the values taken by a polynomial with integer coefficients, it is unclear what the asymptotic number of such smooth values should be; this is in contrast to the related problem of counting the number of prime values of a polynomial, for which Bateman and Horn published a conjectured asymptotic formula that is widely believed to be true. We discuss how to employ the Bateman-Horn conjecture to derive an asymptotic formula for the number of smooth values of a polynomial, with the smoothness parameter in a non-trivial range. This conditional result provides a believable heuristic for the number of smooth integers among all values {F(n)}, and also among the values {F(p)} on prime arguments only.

math.NT↗

arXiv2000

Restoring Fairness to Dukego

In this paper we correct an analysis of the two-player perfect-information game Dukego given in Berlekamp, Conway, and Guy's Winning Ways for your Mathematical Plays (Chapter 19). In particular, we characterize the board dimensions that are fair, i.e., those for which the first player to move has a winning strategy.

math.CO↗

arXiv2000

Compactness Theorems for Geometric Packings

Moser asked whether the collection of rectangles of dimensions 1 x 1/2, 1/2 x 1/3, 1/3 x 1/4, ..., whose total area equals 1, can be packed into the unit square without overlap, and whether the collection of squares of side lengths 1/2, 1/3, 1/4, ... can be packed without overlap into a rectangle of area pi^2/6-1. Computational investigations have been made into packing these collections into squares of side length 1+epsilon and rectangles of area pi^2/6-1+epsilon, respectively, and one can consider the apparently weaker question whether such packings are possible for every positive number epsilon. In this paper we establish a general theorem on sequences of geometrical packings that implies in particular that the ``for every epsilon'' versions of these two problems are actually equivalent to the original tiling problems.

math.MG↗

arXiv1999

Biases in the Shanks-Renyi Prime Number Race

Rubinstein and Sarnak investigated systems of inequalities of the form pi(x;q,a_1) > ... > pi(x;q,a_r), where pi(x;q,a) denotes the number of primes up to x that are congruent to a mod q. They showed, under standard hypotheses on the zeros of Dirichlet L-functions mod q, that the set of positive real numbers x for which these inequalities hold has positive (logarithmic) density delta_{q;a_1,dots,a_r} > 0. They also discovered the surprising fact that a certain distribution associated with these densities is not symmetric under permutations of the residue classes a_j in general, even if the a_j are all squares or all nonsquares mod q (a condition necessary to avoid obvious biases of the type first observed by Chebyshev). This asymmetry suggests, contrary to prior expectations, that the densities delta_{q;a_1,dots,a_r} themselves vary under permutations of the a_j. In this paper, we derive (under the hypotheses used by Rubinstein and Sarnak) a general formula for the densities delta_{q;a_1,dots,a_r}, and we use this formula to calculate many of these densities when q <= 12 and r <= 4. For the special moduli q = 8 and q = 12, and for {a_1,a_2,a_3} a permutation of the nonsquares {3,5,7} mod 8 and {5,7,11} mod 12, respectively, we rigorously bound the error in our calculations, thus verifying that these densities are indeed asymmetric under permutation of the a_j. We also determine several situations in which the densities delta_{q;a_1,dots,a_r} remain unchanged under certain permutations of the a_j, and some situations in which they are provably different.

math.NT↗

arXiv1999

Farmer Ted Goes Natural

A traditional "Farmer Ted" calculus problem is to minimize the perimeter of a rectangular chicken coop given the area N, so that as little as possible will be spent on the fencing. But what if N is an integer, and we are only allowed to consider rectangles with integer side lengths? Often it will be more cost-effective to build a coop with area smaller than N, where the measure of cost-effectiveness is the ratio of the area to the perimeter. Those numbers N that are the areas of rectangles that are more cost-effective than any smaller rectangle are dubbed "almost-squares", in deference to our intuition that such numbers ought to be the product of two nearly equal factors. This paper investigates the characterization and distribution of the almost-squares. It is shown that almost-squares can be equivalently described in a surprisingly elegant way, and that computing whether a number is an almost-square and computing the least almost-square not exceeding N can be done surprisingly efficiently (much faster than factoring integers, for instance). Several bad jokes are included.

math.NT↗