arXiv subjects

David Dekker

Publications and source records attributed to David Dekker.

5 recordsLinked to original sources

arXiv2025

Dynamic Structures of Knowledge Production: Citation Rates in Hydrogen Technologies

We explore a dynamic patent citation network model to explain the established link between network structure and technological improvement rate. This model, a type of survival model, posits that the *dynamic* network structure determines the *constant* improvement rate, requiring consistent structural reproduction over time. The model's hazard rate, the probability of a patent being cited, represents "knowledge production," reflecting the output of new patents given existing ones. Analyzing hydrogen technology patents, we find distinct subdomain knowledge production rates, but consistent development across subdomains. "Distribution" patents show the lowest production rate, suggesting dominant "distribution" costs in $H_2$ pricing. Further modeling shows Katz-centrality predicts knowledge production, outperforming subdomain classification. Lower Katz centrality in "distribution" suggests inherent organizational differences in invention. Exploitative learning (within-subdomain citations) correlates with higher patenting opportunity costs, potentially explaining slower "distribution" development, as high investment needs may incentivize monopolization over knowledge sharing.

econ.GN↗

arXiv2024

A New Method for Inserting Train Paths into a Timetable

A seemingly simple, yet widely applicable subroutine in automated train scheduling is the insertion of a new train path to a timetable in a railway network. We believe it to be the first step towards a new train-rerouting framework in case of large disturbances or maintenance works. Other applications include handling ad-hoc requests and modifying train paths upon request from railway undertakings. We propose a fast and scalable path-insertion algorithm based on dynamic programming that is able to output multiple suitable paths. Our algorithm uses macroscopic data and can run on railway networks with any number of tracks. We apply the algorithm on the line from G\"oteborg S\"aven\"as to the Norwegian border at Kornsj\"o. For a time window of seven hours, we obtain eight suitable paths for a freight train within 0.3 seconds after preprocessing.

cs.DS↗

arXiv2023

Balance Correlations, Agentic Zeros, and Networks: The Structure of 192 Years of War and Peace

Social network extensions of Heider's balance theory have not always been consistent. Structural balance theory primarily focuses on graph partitioning, thereby assuming, homogeneity in balance-driven behavior of nodes. We present a general model and formal notation that permit testing such behavioral assumptions. Specifically, we formulate statements as a comparison of two conditional probabilities of a tie, $Ego\stackrel{q}{\text{-}}Alter$, first conditional on 2-paths $Ego\, \stackrel{r}{\text{-}}\,X\,\stackrel{s}{\text{-}}\,Alter$, and second conditional on all others, $\neg (Ego\,\stackrel{r}{\text{-}}\,X\,\stackrel{s}{\text{-}}\,Alter)$. The key here is that $q$, $r$ and $s$ represent indices of relations in a set of mutually exclusive and exhaustive relations (their sum produces a complete graph). This relaxes the assumption of a signed graph dichotomy. Here we identify neutral as distinct from negative and positive ties. Descriptive statistics measuring the difference in conditional probabilities, or the prevalence for any stipulated balance configuration, are given by the point bi-serial correlations of relation $q$ with the count of $2$-paths (through relations $r$ and $s$). Two major advantages are: direct comparison, even if network sizes and densities differ, and evaluation of specific (un)balance behaviors. We apply this approach on a data set with friendly vs hostile relations between countries from 1816 to 2007. We find strong evidence for one of the four classic Heiderian balance theory predictions, and virtually no evidence in support of the unbalanced predictions. However, we do find stable and surprising evidence that the neutral ties are important in balancing the relations among nations. Results further suggest that prevalence of balance driven behavior varies over time, and that other triadic motivated behaviors prevail among countries in certain eras.

physics.soc-ph↗

arXiv2022

Kernelization for Feedback Vertex Set via Elimination Distance to a Forest

We study efficient preprocessing for the undirected Feedback Vertex Set problem, a fundamental problem in graph theory which asks for a minimum-sized vertex set whose removal yields an acyclic graph. More precisely, we aim to determine for which parameterizations this problem admits a polynomial kernel. While a characterization is known for the related Vertex Cover problem based on the recently introduced notion of bridge-depth, it remained an open problem whether this could be generalized to Feedback Vertex Set. The answer turns out to be negative; the existence of polynomial kernels for structural parameterizations for Feedback Vertex Set is governed by the elimination distance to a forest. Under the standard assumption that NP is not a subset of coNP/poly, we prove that for any minor-closed graph class $\mathcal G$, Feedback Vertex Set parameterized by the size of a modulator to $\mathcal G$ has a polynomial kernel if and only if $\mathcal G$ has bounded elimination distance to a forest. This captures and generalizes all existing kernels for structural parameterizations of the Feedback Vertex Set problem.

cs.DS↗

arXiv2017

Transitivity Correlation: Measuring Network Transitivity as Comparative Quantity

This paper proposes that common measures for network transitivity, based on the enumeration of transitive triples, do not reflect the theoretical statements about transitivity they aim to describe. These statements are often formulated as comparative conditional probabilities, but these are not directly reflected by simple functions of enumerations. We think that a better approach is obtained by considering the linear regression coefficient of ties $i\,\rightarrow\,j$ on the number of two-paths $i\,\rightarrow\,k\rightarrow\,j$ for the $(n-2)$ possible intermediate nodes $k$. Two measures of transitivity based on correlation coefficients between the existence of a tie and the existence, or the number, of two-paths are developed, and called "Transitivity Phi" and "Transitivity Correlation". Some desirable properties for these measures are studied and compared to existing clustering coefficients, in both random (Erdös-Renyi) and in stylized networks (windmills). Furthermore, it is shown that under the condition of zero Transitivity Correlation, the total number of transitive triples is determined by four underlying features of any directed graph: size, density, reciprocity, and the covariance between indegrees and outdegrees. Also, it is demonstrated that plotting conditional probability of ties, given the number of two-paths, provides valuable insights into empirical regularities and irregularities of transitivity patterns.

stat.AP↗