Community detection in networks: Structural communities versus ground truth

Algorithms to find communities in networks rely just on structural information and search for cohesive subsets of nodes. On the other hand, most scholars implicitly or explicitly assume that structural communities represent groups of nodes with similar (non-topological) properties or functions. This hypothesis could not be verified, so far, because of the lack of network datasets with information on the classification of the nodes. We show that traditional community detection methods fail to find the metadata groups in many large networks. Our results show that there is a marked separation between structural communities and metadata groups, in line with recent findings. That means that either our current modeling of community structure has to be substantially modified, or that metadata groups may not be recoverable from topology alone.Comment: 21 pages, 19 figure

Individual Professional Practice in the Company

Import 05/08/2014Tato práce popisuje mé působení ve společnosti netdevelo s.r.o., která se primárně věnuje vývoji internetových obchodů přizpůsobených na míru. Praxi jsem vykonával na pozici programátora na oddělení realizace projektů. V rámci odborné praxe jsem pracoval na interních aplikacích firmy. U dvou aplikací, kterým jsem se věnoval téměř celé období praxe, jsem měl provést analýzu požadavků, návrh a následnou implementaci. První aplikace „Pošťák“ je určena pro evidenci příchozí a odchozí papírové pošty. Druhá aplikace „Pohledávky“ slouží k snadnému vymáhání pohledávek od klientů.This bachelor thesis describes my career in the company netdevelo Ltd. which is primarily specialized in development of customer-tailored e-shops. I worked as programmer in the department Implementation of projects. Within this professional practice I worked on the internal applications of the company. I spent almost all the time of my practice to analyze the requirements, to make a design and subsequent implementation of two applications. The first application named “Pošťák” is designed for recording incoming and outgoing paper mail. The second application named “Pohledávky” is made for easy debt recoveries from clients.460 - Katedra informatikyvelmi dobř

Topological sequence entropy for maps of the circle

summary:A continuous map $f$ of the interval is chaotic iff there is an increasing sequence of nonnegative integers $T$ such that the topological sequence entropy of $f$ relative to $T$, $h_T(f)$, is positive ([FS]). On the other hand, for any increasing sequence of nonnegative integers $T$ there is a chaotic map $f$ of the interval such that $h_T(f)=0$ ([H]). We prove that the same results hold for maps of the circle. We also prove some preliminary results concerning topological sequence entropy for maps of general compact metric spaces

Recent photometry of symbiotic stars - XII

We present new photometric observations of 15 symbiotic stars (EG And, Z And, AE Ara, BF Cyg, CH Cyg, CI Cyg, V1329 Cyg, TX CVn, AG Dra, Draco C-1, RW Hya, SY Mus, AR Pav, AG Peg, AX Per) covering their last orbital cycle(s) from 2003.9 to 2007.2. We obtained our data by both classical photoelectric and CCD photometry. Main results are: EG And brightened by about 0.3 mag in U from 2003. A 0.5 mag deep primary minimum developed in the U light curve (LC) at the end of 2006. Z And continues its recent activity that began during the 2000 autumn. A new small outburst started in summer of 2004 with the peak U-magnitude of about 9.2. During the spring of 2006 the star entered a massive outburst. It reached its historical maximum at U = 8.0 in 2006 July. AE Ara erupted in 2006 February with Dm(vis) approx. 1.2 mag. BF Cyg entered a new active stage in 2006 August. A brightness maximum (U approx. 9.4) was measured during 2006 September. CH Cyg persists in a quiescent phase. During 2006 June - December about 2 mag decline in all colours was measured. CI Cyg started a new active phase during 2006 May - June. After 31 years it erupted by about 2 mag in U. TX CVn maintains a bright stage with U approx. 10.5 from 2003. AG Dra entered a new major outburst in 2006 June. It reached its maximum at U = 8.0 in 2006 September. AR Pav persists at a low level of the activity. AG Peg's LC profile varies markedly during different orbital cycles. AX Per continues its quiescent phase.Comment: 4 pages text, 12 figures, 18 tables, accepted for publication in Astron. Nachrichte