Wolfgang W. Bein

Wolfgang W. Bein
University of Nevada, Las Vegas | UNLV · Department of Computer Science

Dr. rer. nat. (Ph.D.)

About

110
Publications
9,950
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
756
Citations
Additional affiliations
June 1998 - present
University of Nevada, Las Vegas
Position
  • Professor (Full)
June 1994 - June 1998
University of Texas at Dallas
Position
  • Professor (Associate)
July 1992 - June 1994
American Airlines
Position
  • Operation Research Analyst

Publications

Publications (110)
Conference Paper
Full-text available
We consider the classical power management problem: There is a device which has two states ON and OFF and one has to develop a control algorithm for changing between these states as to minimize (energy) cost when given a sequence of service requests. Although an optimal 2-competitive algorithm exists, that algorithm does not have good performance i...
Article
Full-text available
Algorithms for series-parallel graphs can be extended to arbitrary two-terminal dags if node reductions are used along with series and parallel reductions. A node reduction contracts a vertex with unit in-degree (out-degree) into its sole incoming (outgoing) neighbor. This paper gives an O(n2"5) algorithm for minimizing node reductions, based on ve...
Conference Paper
Full-text available
Many open source software projects are not very open to third party developers. The point of open source is to enable anyone to fix bugs or add desired capabilities without holding them hostage to the original developers. This principle is important because an open source project's developers may be unresponsive or unable to meet third party needs,...
Article
Full-text available
We study the concept of series and parallel composition of linear programming problems and show that greedy properties are inherited by such compositions. Our results are inspired by earlier work on compositions of flow problems. We make use of certain Monge properties as well as convexity properties which support the greedy method in other context...
Article
Full-text available
We introduce the novel concept of knowledge states. The knowledge state approach can be used to construct competitive randomized online algorithms and study the trade-off between competitiveness and memory. Many well-known algorithms can be viewed as knowledge state algorithms. A knowledge state consists of a distribution of states for the algorith...
Conference Paper
Problems addressing the generation of random polygons have important applications for evaluating the performance of algorithms on polygonal domains. The standard Voronoi diagram can be applied effectively to determine the service regions of battery exchange stations when all service exchange stations have identical capacity. In real world situation...
Article
Full-text available
We consider a power-down system with two states—“on” and “off”—and a continuous set of power states. The system has to respond to requests for service in the “on” state and, after service, the system can power off or switch to any of the intermediate power-saving states. The choice of states determines the cost to power on for subsequent requests....
Article
Full-text available
We consider the classical power management problem: There is a system or “device” which has two states—ON and OFF—and one has to develop a control algorithm for changing between these states as to minimize cost (energy or some other hybrid cost) when given a sequence of service requests. We analyze this problem in terms of online competitive analys...
Chapter
Power-down mechanisms are well known and are widely used to save energy; these mechanisms are encountered on an everyday basis. We consider a device which has a set of states defined by a continuous function. The state of the device can be switched at any time. In any state the device consumes energy and a power up cost to switch the machine to ful...
Conference Paper
In this paper, we study the grid scheduling problem in a battery exchange station (BES) as a part of the battery consolidation system (BCS). We define the grid scheduling problem as the BES's service scheduling to exchange batteries of electric vehicles (EVs), the battery exchange price scheduling, and the electricity buying scheduling for a day ah...
Chapter
Passenger routing in railway systems has traditionally relied on fixed timetables, working under the assumption that actual performance always matches the planned schedules. The complex variable interplay found in railway networks, however, make it practically impossible for trains to systematically hold the designed timetables as delays are a comm...
Chapter
When people suffer from issues like workplace stress, financial stress, marital stress, family stress, bullying, domestic violence, peer pressure, anxiety, relationship issues, career issues, parenting, loneliness, depression and others, they try to avoid it, either by saying life is just like this or by comparing their problems with others. Distra...
Conference Paper
The concept of the battery exchange station (BES) as a part of the battery consolidation system (BCS) has certain criteria which makes it a significant player of bettery adaptation plan of electric vehicles (EVs) in the grid toward the smart grid (SG). In this paper, we focus on finding an efficient joint capacity and placement planning of BESs amo...
Chapter
Power-down mechanisms are well known and are widely used to save energy; these mechanisms are encountered on an everyday basis. We consider a device which has a set of states defined by a continuous function. The state of the device can be switched at any time. In any state the device consumes energy and a power up cost to switch the machine to ful...
Chapter
During the past decade, the smart grid (SG) concept has been advancing better global acceptance of the electric vehicle (EV) notion. Additionally, the incorporation of renewable energy (RE) resources in the SG is a promising solution to reduce carbon emissions in an intelligent manner. Due to technological barriers at this moment, battery charging...
Article
Full-text available
A power-down system has an on-state, an off-state, and a finite or infinite number of intermediate states. In the off-state, the system uses no energy and in the on-state energy it is used fully. Intermediate states consume only some fraction of energy but switching back to the on-state comes at a cost. Previous work has mainly focused on asymptoti...
Chapter
Power-down mechanisms are well known and are widely used to save energy. We consider a device which has states OFF, ON, and a fixed number of intermediate states. The state of the device can be switched at any time. In the OFF state the device consumes zero energy and in ON state it works at its full power consumption. The intermediate states consu...
Chapter
Today’s recruitment applications are designed not only reduce paperwork but can make a significant contribution to a company’s marketing and sales activity. Recruitment websites and software make possible for managers to access information crucial to managing their staff, which they can use for promotion decisions, payroll considerations and hiring...
Conference Paper
The mini-track “Decision Support for Complex Networks” invited contributions in the area of complex decision support under multiple criteria and where a multitude of variables have to be considered under great uncertainty. Typically, such systems are used for crisis and risk management in diverse contexts, such as health care, homeland security, av...
Technical Report
Full-text available
Theme The International Conference on Information Technology-New Generations (ITNG) is an annual event focusing on state of the art technologies pertaining to digital information and communications. The applications of advanced information technology to such domains as astronomy, biology, education, geosciences, health care and security are among t...
Conference Paper
In this paper, the frequency of trains in the Munich subway network is analyzed. Using influence diagrams the stations and edges in the network that are most vulnerable to catastrophic attacks are determined. Upon obtaining the number of trains in each station at a certain moment in time, the most vulnerable stations will be automatically identifie...
Chapter
We explore options for integrating sustainable and renewable energy into the existing power grid, or even create a new power grid model. We present various theoretical concepts necessary to meet the challenges of a smart grid. We first present a supply and demand model of the smart grid to compute the average number of conventional power generator...
Chapter
The black and white bin packing problem is a variant of the classical bin packing problem, where in addition to a size, each item also has a color (black or white), and in each bin the colors of items must alternate. The problem has been studied extensively, but the best competitive online algorithm has competitiveness of 3. The competitiveness of...
Article
Power-down mechanisms are well known and are widely used to save energy, these mechanisms are encountered on an everyday basis. We consider a device which has states OFF, ON, and a fixed number of intermediate states. The state of the device can be switched at any time. In the OFF state the device consumes zero energy and in ON state it works at it...
Article
The most common approach for border patrol operations is the use of human personnel and manned ground vehicles, which is expensive, at times inefficient and sometimes even hazardous to people involved. A better approach would be using Unmanned Aerial Vehicles (UAVs) in combination with such ground sensors. This would help improve the overall effect...
Article
Full-text available
This paper introduces the use of conditional-value-at-risk (CVaR) as a criterion for stochastic scheduling problems. This criterion has the tendency of simultaneously reducing both the expectation and variance of a performance measure, while retaining ...
Chapter
This is an overview over dynamic programming with an emphasis on advanced methods. Problems discussed include path problems, construction of search trees, scheduling problems, applications of dynamic programming for sorting problems, server problems, as well as others. This chapter contains an extensive discussion of dynamic programming speedup. Th...
Conference Paper
A randomized on-line algorithm is given for the 2-server problem on the line, with competitiveness less than 1.901 against the oblivious adversary. This improves the previously best known competitiveness of 15578 ≈ 1.987 for the problem. The algorithm uses a new approach and defines a potential in terms of isolation indices from T-theory.
Article
Full-text available
The minitrack on Open Movements is introduced.
Article
Full-text available
Block sorting is used in connection with Optical Character Recognition (OCR). Recent work has focused on finding good strategies which work in practice. In this paper, we show that optimizing block sorting is -hard. Along with this result, we give new non-trivial lower bounds. These bound can be computed efficiently. We define the concept of "Local...
Article
It has been a long-standing open problem to determine the exact randomized competitiveness of the 2-server problem, that is, the minimum competitiveness of any randomized online algorithm for the 2-server problem. For deterministic algorithms the best competitive ratio that can be obtained is 2 and no randomized algorithm is known that improves thi...
Conference Paper
Full-text available
We study the problem of allocating memory of servers in a data center based on online requests for storage. Given an online sequence of storage requests and a cost associated with serving the request by allocating space on a certain server one seeks to select the minimum number of servers as to minimize total cost. We use two different algorithms a...
Conference Paper
Full-text available
Large corporations such as Amazon, Google, Microsoft, and Yahoo, use data centers to keep up with the growing demand for communication-hungry Internet services like image and video sharing, social networking, and searching. We study the problem of actually allocating the memory of servers in a data center based on online requests for storage. Given...
Article
Batching has been studied extensively in the offline case, but applications such as manufacturing or TCP acknowledgment often require online solutions.We consider online batching problems, where the order of jobs to be batched is fixed and where we seek to minimize the sum of the completion times of the jobs. We present optimally competitive online...
Article
Full-text available
We consider the online list s-batch problem, where all the jobs have processing time 1 and we seek to minimize the sum of the completion times of the jobs. We give a Java program which is used to verify that the competitiveness of this problem is 619/583.
Article
The block sorting problem is the problem of minimizing the number of steps to sort a list of distinct items, where a sublist of items which are already in sorted order, called a block, can be moved in one step. We give an approximation algorithm for the block sorting problem with an approximation ratio of and run time . The approximation algorithm...
Article
Full-text available
Multiprocessor systems with a global shared memory provide logically uniform data access. To hide latencies when accessing global memory each processor makes use of a private cache. Several copies of a data item may exist concurrently in the system. To guarantee consistency when updating an item a processor must invalidate copies of the item in oth...
Article
Full-text available
We study the coverage problem for sensor networks from the fault tolerance and reliability point of view. Fault tolerance is a critical issue for sensors deployed in places where they are not easily replaceable, repairable and rechargeable. Failure of one node should not incapacitate the entire network. We propose three 1-fault tolerant topologies,...
Conference Paper
Full-text available
Suppose there are n applications and n processors. A pair cover is a set S of one-to-one mappings (assignments) of the applications to the processors such that, for every pair (Ai,Aj) of applications and every pair (p,q) of processors, there is an assignment f in S that maps (Ai,Aj) to (p,q). More generally, we consider, for all k/spl ges/1, minimu...
Article
Full-text available
A technique for clustering data by common attribute values involves grouping rows and columns of a binary matrix to make the minimum number of submatrices all 1's. As binary matrices can be viewed as adjacency matrices of bipartite graphs, the problem is equivalent to partitioning a bipartite graph into the smallest number of complete bipartite sub...
Conference Paper
Full-text available
We prove that there exists a randomized online algorithm for the 2-server 3-point problem whose expected competitive ratio is at most 1.5897. This is the first nontrivial upper bound for randomized k-server algorithms in a general metric space whose competitive ratio is well below the corresponding deterministic lower bound (= 2 in the 2-server cas...
Conference Paper
Full-text available
In scheduling, the two machine flow shop problem F2parSigma C<sub>i</sub> is to find a schedule that minimizes the sum of finishing times of an arbitrary number of jobs that need to be executed on two machines, such that each job must complete processing on machine 1 before starting on machine 2. Finding such a schedule is NP-hard [6]. We propose a...
Article
Full-text available
The bin packing with rejection problem is the following: Given a list of items with associated sizes and rejection costs, find a packing into unit bins of a subset of the list, such that the number of bins used plus the sum of rejection costs of unpacked items is minimized. In this paper, we first show that bin packing with rejection can be reduced...
Article
In ubiquitous computing the user is surrounded by many computational devices and systems Ordinary actions and different parameter values of the environment being sensed by these devices trigger actions of which the user may not necessarily be aware Privacy protection as part of network security refers to the protection of sensitive, personal inform...
Article
We give a randomized algorithm (the “Wedge Algorithm”) of competitiveness 32Hk−12k for any metrical task system on a uniform space of k points, for any k⩾2, where Hk=∑i=1k1i, the kth harmonic number. This algorithm has better competitiveness than the Irani–Seiden algorithm if k is smaller than 108. The algorithm is better by a factor of 2 if k47.
Conference Paper
Full-text available
It has been a long-standing open problem to determine the exact randomized competitiveness of the 2-server problem, that is, the minimum competitiveness of any randomized online algorithm for the 2-server problem. For deterministic algorithms the best competitive ratio that can be obtained is 2 and no randomized algorithm is known that improves thi...
Conference Paper
Full-text available
The randomized k-paging algorithm Equitable given by Achlioptas et al. is H k -competitive and uses O(k 2 logk) memory. This competitive ratio is best possible. The randomized algorithm RMark given by Fiat et al. is (2H k − 1)-competitive, but only uses O(k) memory. Borodin and El Yaniv [6] list as an open question whether there exists an H k -comp...
Article
Full-text available
We introduce the concept of knowledge states; many well-known algorithms can be viewed as knowledge state algorithms. The knowledge state approach can be used to to construct competitive randomized online algorithms and study the tradeoff between competitiveness and memory. A knowledge state simply states conditional obligations of an adversary, by...
Conference Paper
“Bin packing with rejection” is the following problem: Given a list of items with associated sizes and rejection costs, find a packing into unit bins of a subset of the list such that the number of bins used plus the sum of rejection costs of unpacked items is minimized. We show that bin packing with rejection can be reduced to n multiple knapsack...
Article
Full-text available
When employed by a company, in almost all the cases a new employee has to sign an agreement giving the company exclusive rights to any intellectual property developed as part of their work assignments. This agreement could extend beyond a change of jobs and cause conflict of interests in new employment situations. A patent is a government-granted m...
Article
Full-text available
A copyright provides protection for original artistic or literary work and is valid for the life of the owner plus 70 years. There is a growing tension between creative practices that require access to content that is often copyrighted, and increasingly restrictive intellectual property laws and policies governing access to copyrighted content. Ver...
Article
Full-text available
We consider here the one-machine serial batching problem under weighted average completion. This problem is known to be $cal Ncal P$-hard and no good approximation algorithms are known. Batching has wide application in manufacturing, decision management, and scheduling in information technology.We give an approximation algorithm with approximation...
Conference Paper
Full-text available
There exist several general techniques in the literature for speeding up naive implementations of dynamic programming. Two of the best known are the Knuth-Yao quadrangle inequality speedup and the SMAWK algorithm for finding the row-minima of totally monotone matrices. Although both of these techniques use a quadrangle inequality and seem similar,...
Conference Paper
Full-text available
We introduce a new version of the server problem: the delayed server problem. In this problem, once a server moves to serve a request, it must wait for one round to move again, but could serve a repeated request to the same point. We show that the delayed k-server problem is equivalent to the (k–1)-server problem in the uniform case, but not in gen...
Conference Paper
Full-text available
Block sorting is used in connection with optical character recognition (OCR). Recent work has focused on finding good strategies which perform well in practice. Block sorting is \(\mathcal{NP}\)-hard and all of the previously known heuristics lack proof of any approximation ratio. We present here an approximation algorithm for the block sorting pro...
Conference Paper
Full-text available
We study the coverage problem from the fault tolerance point of view for sensor networks. Fault tolerance is a critical issue for sensors deployed in places where are not easily replaceable, repairable and rechargeable. The failure of one node should not incapacitate the entire network. We propose three 1 fault tolerant models, and we compare them...
Article
We give algorithmic results for combinatorial problems with cost arrays possessing certain algebraic Monge properties. We extend Monge-array results for two shortest path problems to a general algebraic setting, with values in an ordered commutative semigroup, if the semigroup operator is strictly compatible with the order relation.We show how our...
Conference Paper
Full-text available
We give a randomized algorithm (the "Wedge Algorithm") of competitiveness for any metrical task system on a uniform space of k points. This algorithm has better competitiveness than the Irani-Seiden algorithm if k is smaller than 10<sup>8</sup>. The algorithm is better by a factor of 2 if k < 47.
Conference Paper
We introduce the novel concept of knowledge states. A knowledge state simply states conditional obligations of an adversary, by fixing a work function, and gives a distribution for the algorithm. When a knowledge state algorithm receives a request, it then calculates one or more “subsequent” knowledge states, together with a probability of transiti...
Article
Full-text available
We present an optimal embedding of a honeycomb network (honeycomb mesh and honeycomb torus) of size n into a hypercube with expansion ratio of 4/3 ≈ 1.33 when n is a power of two. When n is not a power of two, the expansion is 16/3 ≈ 5.33, which we conjecture to be near optimal. For a honeycomb mesh, the dilation of the embedding is 1. For a honeyc...
Conference Paper
Full-text available
Batching has been studied extensively in the offline case, but many applications such as manufacturing or TCP acknowledgement require online solutions. We consider online batching problems, where the order of jobs to be batched is fixed and where we seek to minimize average flow time. We present optimally competitive algorithms for s-batch (compet...
Article
Full-text available
We describe total congestion 1 embeddings of complete binary trees into three dimensional grids with low expansion ratio r. That is, we give a one-to-one embedding of any complete binary tree into a hexahedron shaped grid such that (a) the number of nodes in the grid is at most r times the number of nodes in the tree, and (b) no tree nodes or edges...
Conference Paper
Full-text available
Multiprocessor systems with a global shared memory provide logically uniform data access. To hide latencies when accessing global memory each processor makes use of a private cache. Several copies of a data item may exist concurrently in the system. To guarantee consistency when updating an item a processor must invalidate copies of the item in oth...
Article
In the k-server problem we wish to minimize, in an online fashion, the movement cost of k servers in response to a sequence of requests (we assume that k greater than or equal to 2). The request issued at each step is specified by a point r in a given metric space M. To serve this request, one of the k servers must move to r. It is known that if M...
Conference Paper
Full-text available
We present an efficient algorithm called the Quadtree Heuristic for identifying a list of similar terms for each unique term in a large document collection. Term similarity is defined using the expected mutual information measure (EMIM). Since our aim for defining the similarity lists is to improve information retrieval (IR), we present the outcome...
Conference Paper
Full-text available
When restricted to cost arrays possessing the sum Monge property, many combinatorial optimization problems with sum objec- tive functions become significantly easier to solve. The more general algebraic assignment and transportation problems are similarly easier to solve given cost arrays possessing the corresponding algebraic Monge property. We sh...
Conference Paper
We describe total congestion 1 embeddings of complete binary trees into three dimensional grids with a fixed number of layers. More specifically, we give a one-to-one embedding of any complete binary tree into a hexahedron shaped grid such that no tree nodes or edges occupy the same grid positions. With 7 layers, the number of nodes in the grid is...
Conference Paper
Block sorting is used in connection with optical character recognition (OCR). Recent work has focused on finding good strategies which work in practice. We show that optimizing block sorting is NP-hard. Along with this result, we give new non-trivial lower bounds. These bounds can be computed efficiently. We define the concept of local property alg...
Article
An efficient randomized online algorithm for the paging problem for cache size 2 is given, which is -competitive against an oblivious adversary. The algorithm keeps track of at most one page in slow memory at any time. A lower bound of is given for the competitiveness of any trackless online algorithm for the same problem, i.e., an algorithm that k...
Article
A class of "simple" online algorithms for the k-server problem is identified. This class, for which the term trackless is introduced, includes many known server algorithms. The k-server conjecture fails for trackless algorithms. A lower bound of 23/11 on the competitiveness of any deterministic trackless 2-server algorithm and a lower bound of 1 +...
Conference Paper
Full-text available
We describe total congestion 1 embeddings of complete binary trees into three dimensional grids with expansion ratios 1.172 and 1.25. That is, we give a one-to-one embedding of any complete binary tree into a hexahedron shaped grid such that: the number of nodes in the grid is at most 1.172 (1.25) times the number of nodes in the tree; and no tree...
Conference Paper
In the k-Server Problem we wish to minimize, in an online fashion, the movement cost of k servers in response to a sequence of requests. The request issued at each step is specified by a point r in a given metric space M. To serve this request, one of the k servers must move to r. (We assume that k ≥ 2.) It is known that if M has at least k + 1 poi...
Article
Full-text available
In the k-Server Problem we wish to minimize, in an online fashion, the movement cost of k servers in response to a sequence of requests. The request issued at each step is speciied by a point r in the given metric space, and one of the k servers must be moved to r. An online algorithm for this problem is called C-competitive if its cost on any requ...
Article
Full-text available
The concept of tracklessness , an information flow restriction for online algorithms, similar in some sense to memorylessness, is introduced. A number of well-known algorithms are trackless, for example, BALANCE and HARMONIC. New lower bounds are obtained for the competitiveness of trackless algorithms for the 2-server problem. An open question by...
Article
Full-text available
When restricted to cost arrays possessing the sum Monge property, many combinatorial optimization problems with sum objective functions become significantly easier to solve. (An array A = fa[i; j]g possesses the sum Monge property if for all i ! k and j ! `, a[i; j] + a[k; `] a[i; `] + a[k; j].) Examples include the usual sum-objective-function ver...
Article
Full-text available
. Algorithms for series-parallel graphs can be extended to arbitrary two-terminal dags if node reductions are used along with series and parallel reductions. A node reduction contracts a vertex with unit in-degree (out-degree) into its sole incoming (outgoing) neighbor. We give an O(n 2:5 ) algorithm for minimizing node reductions, based on vertex...
Article
In 1963, Hoffman gave necessary and sufficient conditions under which a family of O(mn)-time greedy algorithms solves the classical two-dimensional transportation problem with m sources and n sinks. One member of this family, an algorithm based on the “northwest corner rule”, is of particular interest, as its running time is easily reduced to O(m +...
Article
The support of Boolean set operations in free-form solid modeling systems requires the repeated intersection of parametric surfaces. Present approaches to this problem are sequential and must make trade-offs between accuracy, robustness and efficiency. In this paper, we investigate a parallel approach to the surface intersection problem that shows,...