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Helmut Prodinger

Publications and source records attributed to Helmut Prodinger.

At least 55 records · Page 3Linked to original sources
arXiv2021

Weighted unary-binary trees, Hex-trees, marked ordered trees, and related structures

Hex-trees are identified as a particular instance of weighted unary-binary trees. The Horton-Strahler numbers of these objects are revisited, and, thanks to a substitution that is not immediately intuitive, explicit results are possible. They are augmented by asymptotic evaluations as well. Furthermore, marked ordered trees (in bijection to skew Dyck paths) are investigated, followed 3-Motzkin paths and multi-edge trees. The underlying theme is sequence A002212 in the Encyclopedia of integer sequences.

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arXiv2021

A matrix with sums of Catalan numbers -- LU-decomposition and determinant

Following Benjamin et al., a matrix with entries being sums of two neighbouring Catalan numbers is considered. Its LU-decomposition is given, by guessing the results and later prove it by computer algebra, with lots of human help. Specializing a parameter, the determinant turns out to be a Fibonacci number with odd index, confirming earlier results, obtained back then by combinatorial methods.

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arXiv2021

Enumeration of Deutsch paths by adding the adding-a-new-slice method and applications

A variation of Dyck paths allows for down-steps of arbitrary length, not just one. This is motivated by ideas due to Emeric Deutsch. We use the adding-a-new-slice technique and the kernel method to compute the number of maximal runs of up-step runs of length 1 and a subclass of Deutsch paths satisfying a condition that was stipulated by R. Stanley for Dyck paths.

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arXiv2021

The amplitude of Motzkin paths

The amplitude of Motzkin paths was recently introduced, which is basically twice the height. We analyze this parameter using generating functions.

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arXiv2021

Philippe Flajolet's early work in combinatorics

Some of Philippe Flajolet's combinatorial contributions that he wrote between 1976 and 1995, say, are described. In most of Flajolet's papers, asymptotic/analytic considerations play a major role. To be true to the spirit of the journal ECA, the emphasis is on the \emph{combinatorial} part. Covered are Register function of binary trees, approximate counting, digital search trees and the Rice formula, probabilistic counting, adding a new slice, Ramanujan's influence, finite differences and harmonic numbers, Digits and the Mellin-Perron formula.

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arXiv2020

Summing a family of generalized Pell numbers

A new family of generalized Pell numbers was recently introduced and studied by Bród \cite{Dorota}. These number possess, as Fibonacci numbers, a Binet formula. Using this, partial sums of arbitrary powers of generalized Pell numbers can be summed explicitly. For this, as a first step, a power $P_n^l$ is expressed as a linear combination of $P_{mn}$. The summation of such expressions is then manageable using generating functions. Since the new family contains a parameter $R=2^r$, the relevant manipulations are quite involved, and computer algebra produced huge expressions that where not trivial to handle at times.

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arXiv2020

On the enumeration of Hoppy's walks

The enumeration of k-Dyck paths ending at level j after m up-steps, where the last step is an up-step, is given as a sum, improving on a previous formula given by Deng and Mansour.

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arXiv2020

Combinatorics arising from lax colimits of posets

In this paper we study maximal chains in certain lattices constructed from powers of chains by iterated lax colimits in the $2$-category of posets. Such a study is motivated by the fact that in lower dimensions, we get some familiar combinatorial objects such as Dyck paths and Kreweras walks.

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arXiv2020

On some problems about ternary paths -- a linear algebra approach

Ternary paths consist of an up-step of one unit, a down-step of two units, never go below the $x$-axis, and return to the $x$-axis. This paper addresses the enumeration of partial ternary paths, ending at a given level $i$, reading the path either from left to right or from right to left. Since the paths are not symmetric w.r.t.\ left vs.\ right, as classical Dyck paths, this leads to different results. The right to left enumeration is quite challenging, but leads at the end to very satisfying results. The methods are elementary (solving systems of linear equations). In this way, several conjectures left open in Naiomi Cameron's Ph.D. thesis could be successfully settled.

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arXiv2020

Retakh's Motzkin paths and some combinatorial comments

Dyck paths where peaks are only allowed on level 1 and on even-indexed levels, were introduced by Retakh and analysed by Zeilberger, with assistance from Ekhad. We add some combinatorial comments to the enumeration, which involves Motzkin numbers, in particular, about the average height of such objects.

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arXiv2020

On k-Dyck paths with a negative boundary

Paths that consist of up-steps of one unit and down-steps of $k$ units, being bounded below by a horizontal line $-t$, behave like $t+1$ ordered tuples of $k$-Dyck paths, provided that $t\le k$. We describe the general case, allowing $t$ also to be larger. Arguments are bijective and/or analytic.

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arXiv2020

How to sum powers of balancing numbers efficiently

Balancing numbers possess, as Fibonacci numbers, a Binet formula. Using this, partial sums of arbitrary powers of balancing numbers can be summed explicitly. For this, as a first step, a power $B_n^l$ is expressed as a linear combination of $B_{mn}$. The summation of such expressions is then easy using generating functions.

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arXiv2020

A bijection between two subfamilies of Motzkin paths

Two subfamilies of Motzkin paths, with the same numbers of up, down, horizontal steps were known to be equinumerous with ternary trees and related objects. We construct a bijection between these two families that does not use any auxiliary objects, like ternary trees.

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