Papers by Rudolf Fleischer
ACM SIGCSE Bulletin
Visualization technology can be used to graphically illustrate various concepts in computer scien... more Visualization technology can be used to graphically illustrate various concepts in computer science. We argue that such technology, no matter how well it is designed, is of little educational value unless it engages learners in an active learning activity. Drawing on a review of experimental studies of visualization effectiveness, we motivate this position against the backdrop of current attitudes and best practices with respect to visualization use. We suggest a new taxonomy of learner engagement with visualization technology. Grounded in Bloom's wellrecognized taxonomy of understanding, we suggest metrics for assessing the learning outcomes to which such engagement may lead. Based on these taxonomies of engagement and effectiveness metrics, we present a framework for experimental studies of visualization effectiveness. Interested computer science educators are invited to collaborate with us by carrying out studies within this framework.
... also would like to thank the organizing committee, most notably Gerhard Trippen, for their tr... more ... also would like to thank the organizing committee, most notably Gerhard Trippen, for their tremendous work in making ISAAC 2004 a ... Organization IX Referees Pankaj Agarwal Heekap Ahn Amihood Amir Nikhil Bansal Marcin Bienkowski Johannes Blomer Carsten Boke Franz. ...
ACM SIGCSE Bulletin, 2003
The educational impact of visualization depends not only on how well students learn when they use... more The educational impact of visualization depends not only on how well students learn when they use it, but also on how widely it is used by instructors. Instructors believe that visualization helps students learn. The integration of visualization techniques in classroom instruction, however, has fallen far short of its potential. This paper considers this disconnect, identifying its cause in a failure to understand the needs of a key member in the hierarchy of stakeholders, namely the instructor. We describe these needs and offer guidelines for both the effective deployment of visualizations and the evaluation of instructor satisfaction. We then consider different forms of evaluation and the impact of student learning styles on learner outcomes.
ACM SIGCSE Bulletin, 2003
Visualization technology can be used to graphically illustrate various concepts in computer scien... more Visualization technology can be used to graphically illustrate various concepts in computer science. We argue that such technology, no matter how well it is designed, is of little educational value unless it engages learners in an active learning activity. Drawing on a review of experimental studies of visualization effectiveness, we motivate this position against the backdrop of current attitudes and best practices with respect to visualization use. We suggest a new taxonomy of learner engagement with visualization technology. Grounded in Bloom's wellrecognized taxonomy of understanding, we suggest metrics for assessing the learning outcomes to which such engagement may lead. Based on these taxonomies of engagement and effectiveness metrics, we present a framework for experimental studies of visualization effectiveness. Interested computer science educators are invited to collaborate with us by carrying out studies within this framework.
Lecture Notes in Computer Science, 2007
Given an acyclic directed graph and two distinct nodes s and t, we consider the problem of findin... more Given an acyclic directed graph and two distinct nodes s and t, we consider the problem of finding k disjoint paths from s to t satisfying some objective. We consider four objectives, MinMax, Balanced, MinSum-MinMin, and MinSum-MinMax. We use the algorithm by Perl-Shiloach and labelling and scaling techniques to devise an FPTAS for the first three objectives. For the forth one, we propose a general and efficient polynomial-time algorithm.
Lecture Notes in Computer Science, 2009
We evaluate the performance of FPT algorithms for the directed feedback vertex set problem (DFVS)... more We evaluate the performance of FPT algorithms for the directed feedback vertex set problem (DFVS). We propose several new data reduction rules for DFVS. which can significantly reduce the search space. We also propose various heuristics to accelerate the FPT search. Finally, we demonstrate that DFVS is not more helpful for deadlock recovery (with mutex locks) than simple cycle detection.
Theoretical Computer Science, 2006
Accurate network flow measurement is important for a variety of network applications, where the "... more Accurate network flow measurement is important for a variety of network applications, where the "flow" over an edge in the network is intuitively the rate of data traffic. The problem of efficiently monitoring the network flow can be regarded as finding the minimum weight weak vertex cover for a given graph. In this paper, we present a (2 − 2 (G) )-approximation algorithm solving for this problem, which improves previous results, where (G) is the cyclomatic number of G.
Lecture Notes in Computer Science, 2010
Lecture Notes in Computer Science, 2006
We give logarithmic approximation algorithms for the nonmetric uncapacitated multicommodity and m... more We give logarithmic approximation algorithms for the nonmetric uncapacitated multicommodity and multilevel facility location problems. The former algorithms are optimal up to a constant factor, the latter algorithm is far away from the lower bound, but it is the first algorithm to solve the general multilevel problem. To solve the multicommodity problem, we also define a new problem, the friendly tour operator problem, which we approximate by a greedy algorithm.
Lecture Notes in Computer Science, 2010
We study the minimum diameter color-spanning set problem which has recently drawn some attention ... more We study the minimum diameter color-spanning set problem which has recently drawn some attention in the database community. We show that the problem can be solved in polynomial time for L1 and L∞ metrics, while it is NP-hard for all other Lp metrics even in two dimensions. However, we can efficiently compute a constant factor approximation.
Lecture Notes in Computer Science, 2009
... of images and the picture taking device, that can be exploited to guide the upscaling process... more ... of images and the picture taking device, that can be exploited to guide the upscaling process. ... space of original images mapped to the same target image is growing very fast with increasing ... rithm itself is probably not really new, some people might call it a vectorization technique ...
International Journal of Computational Geometry & Applications
Wuhan Daxue Xuebao/Journal of Wuhan University
Introduction As researchers in theoretical or practical computer science, we are used to publishi... more Introduction As researchers in theoretical or practical computer science, we are used to publishing our results in form of research papers that appear in conference proceedings or journals. Journals are normally considered more prestigious than conference proceedings because their more rigorous refereeing standards presumably guarantee a higher quality of the published research papers. This well-established practice of publishing research results puts real practical researchers whose main interest is to write software at a certain disadvantage. There is no established way to `publish' software (except for describing the software in a companion paper that may be considered publishable) unless you want to go the long way of commercializing your system. But this usually only makes sense for certain large systems. Therefore, all the e#ort that goes into the development of smaller programs is usually not rewarded by the academic community because there is no way to make these little ...
The standard dynamic programming solution to finding k- medians on a line with n nodes requires O... more The standard dynamic programming solution to finding k- medians on a line with n nodes requires O(kn ) time. Dynamic programming speed-up techniques, e.g., use of the quadrangle inequality or properties of totally monotone matrices, can reduce this to O(kn) time but these techniques are inherently static. The major result of this paper is to show that we can maintain the dynamic programming speedup in an online setting where points are added from left to right on a line.
We consider a problem coming from practical applications: finding a minimum spanning tree with bo... more We consider a problem coming from practical applications: finding a minimum spanning tree with both edge weights and inner node (non-leaf node) weights. This problem is NP-complete even in the metric space. We present two polynomial time algorithms which achieve approximation factors of 2.35 ln n and 2(Hn − 1), respectively, where n is the number of nodes in the graph and Hn is the n-th Harmonic number. This nearly matches the lower bound: no polynomial-time approximation algorithm can achieve an approximation factor of (1−)Hn, for any > 0. For metric case where the edge weights are symmetric and satisfy the triangle inequality, it also proves to be an NP-hard problem and we give a 3.52 approximation algorithm and an improved factor 3.106 one and also show that an approximation factor of 1.463 is impossible unless N P ⊆ DT IM E[n O(loglogn) ]. We also give an approximation algorithm with factor ∆ − 1, where ∆ is the maximum degree of the graph.
How e#ciently can we search an unknown environment for a goal in unknown position? How much would... more How e#ciently can we search an unknown environment for a goal in unknown position? How much would it help if the environment were known? We answer these questions for simple polygons and for general graphs, by providing online search strategies that are as good as the best o#ine search algorithms, up to a constant factor. For other settings we prove that no such online algorithms exist.
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Papers by Rudolf Fleischer