Log-convexity of combinatorial sequences from their convexity
نویسندگان
چکیده
منابع مشابه
Log–convexity of Combinatorial Sequences from Their Convexity
A sequence (xn)n 0 of positive real numbers is log-convex if the inequality xn xn−1xn+1 is valid for all n 1 . We show here how the problem of establishing the log-convexity of a given combinatorial sequence can be reduced to examining the ordinary convexity of related sequences. The new method is then used to prove that the sequence of Motzkin numbers is log-convex.
متن کاملOn the log-convexity of combinatorial sequences
Here presented is a survey for the log-convexity of some famous combinatorial sequences. We develop techniques for dealing with the log-convexity of sequences satisfying a three-term recurrence. We also introduce the concept of q-log-convexity and establish the link with linear transformations preserving the log-convexity. MSC: 05A20; 11B73; 11B83; 11B37
متن کاملA Criterion for the Log-Convexity of Combinatorial Sequences
Recently, Došlić, and Liu and Wang developed techniques for dealing with the log-convexity of sequences. In this paper, we present a criterion for the log-convexity of some combinatorial sequences. In order to prove the log-convexity of a sequence satisfying a three-term recurrence, by our method, it suffices to compute a constant number of terms at the beginning of the sequence. For example, i...
متن کاملConvexity and Log Convexity for the Spectral Radius
The starting point of this paper is a theorem by J. F. C. Kingman which asserts that if the entries of a nonnegative matrix are log convex functions of a variable then so is the spectral radius of the matrix. A related result of J. Cohen asserts that the spectral radius of a nonnegative matrix is a convex function of the diagonal elements. The first section of this paper gives a new, unified pr...
متن کاملBell Numbers, Log-concavity, and Log-convexity
Let fb k (n)g 1 n=0 be the Bell numbers of order k. It is proved that the sequence fb k (n)=n!g 1 n=0 is log-concave and the sequence fb k (n)g 1 n=0 is log-convex, or equivalently, the following inequalities hold for all n 0, 1 b k (n + 2)b k (n) b k (n + 1) 2 n + 2 n + 1 : Let f(n)g 1 n=0 be a sequence of positive numbers with (0) = 1. We show that if f(n)g 1 n=0 is log-convex, then (n)(m) (n...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
ژورنال
عنوان ژورنال: Journal of Mathematical Inequalities
سال: 2009
ISSN: 1846-579X
DOI: 10.7153/jmi-03-43