A stopping rule while searching for optimal solution of facility-location

Solutions to combinatorial optimization, such as p-median problems of locating facilities, frequently rely on heuristics to minimize the objective function. The minimum is sought iteratively and a criterion is needed to decide when the procedure (almost) attains it. However, pre-setting the number of iterations dominates in OR applications, which implies that the quality of the solution cannot be ascertained. A small branch of the literature suggests using statistical principles to estimate the minimum and use the estimate for either stopping or evaluating the quality of the solution. In this paper we use test-problems taken from Baesley's OR-library and apply Simulated Annealing on these p-median problems. We do this for the purpose of comparing suggested methods of minimum estimation and, eventually, provide a recommendation for practioners. An illustration ends the paper being a problem of locating some 70 distribution centers of the Swedish Post in a region.

Jämförande analys mellan svenska och portugisiska reklambyråer. : Saker som är bra att veta om man ska arbeta som grafisk formgivare i Sverige eller i Portugal

If you move from Sweden to Portugal to work as an Art Director at an Ad agency, there are certain things you ought to know. Perhaps even before you decide to move. There are a lot of things that are quite different if you compare Portugal to Sweden, not only the language, but also the design, software, working hours and much more. You have for example two month with double salary, you work till six p.m. and when it comes to maternity leave, you have 100% compensation with no taxes the first four months of every pregnancy. The tasks you have to handle as an Art Director in Portugal may, as in Sweden, be various. The difference is more how you solve your task and what the design looks like. As a Swede in Portugal the solution will probably look like a mixture between the Portuguese “expressive” and the Swedish “clean” design. This degree project discusses questions that might turn up when a Swede gets employed as an Art Director in Portugal. What will the salary be? When, in the morning, is it time to show up at the office? How many weeks of vacations are entitled? There are a lot of distinctions, but also a lot of similarities. The report is mainly based upon the author’s own experiences of the Ad agency McCann-Erickson in Lisbon. The history of McCann-Erickson starts in New York, 1930 and grew rapidly into one of the leading corporation with agencies all over the world. It is still today one of the world’s largest Ad company with clients like Coca-Cola and General Motors, and the slogan “truth well told” still lights up all their agencies after almost a century, just like a leading star.

Load balancing solution and evaluation of F5 content switch equipment

The Thesis focused on hardware based Load balancing solution of web traffic through a load balancer F5 content switch. In this project, the implemented scenario for distributing HTTPtraffic load is based on different CPU usages (processing speed) of multiple member servers.Two widely used load balancing algorithms Round Robin (RR) and Ratio model (weighted Round Robin) are implemented through F5 load balancer. For evaluating the performance of F5 content switch, some experimental tests has been taken on implemented scenarios using RR and Ratio model load balancing algorithms. The performance is examined in terms of throughput (bits/sec) and Response time of member servers in a load balancing pool. From these experiments we have observed that Ratio Model load balancing algorithm is most suitable in the environment of load balancing servers with different CPU usages as it allows assigning the weight according to CPU usage both in static and dynamic load balancing of servers.

Applicatiion of Almost ideal demand system for a pharmaceutical

This thesis is an application of the Almost Ideal Demand System approach of Deaton and Muellbauer,1980, for a particular pharmaceutical, Citalopram, in which GORMAN´s (1971) multi-stage budgeting approach is applied basically since it is one of the most useful approach in estimating demand for differentiated products. Citalopram is an antidepressant drug that is used in the treatment of major depression. As for most other pharmaceuticals whose the patent has expired, there exist branded and generic versions of Citalopram. This paper is aimed to define its demand system with two stage models for the branded version and five generic versions, and to show whether generic versions are able to compete with the branded version. I calculated the own price elasticities, and it made me possible to compare and make a conclusion about the consumers’ choices over the brand and generic drugs. Even though the models need for being developed with some additional variables, estimation results of models and uncompensated price elasticities indicated that the branded version has still power in the market, and generics are able to compete with lower prices. One important point that has to be taken into consideration is that the Swedish pharmaceutical market faced a reform on October 1, 2002, that aims to make consumer better informed about the price and decrease the overall expenditures for pharmaceuticals. Since there were not significantly enough generic sales to take into calculation before the reform, my paper covers sales after the reform.

Heat losses and thermal performance of commercial combined solar and pellet heating systems

Various pellet heating systems are marketed in Sweden, some of them in combination with a solar heating system. Several types of pellet heating units are available and can be used for a combined system. This article compares four typical combined solar and pellet heating systems: System 1 and 2 two with a pellet stove, system 3 with a store integrated pellet burner and system 4 with a pellet boiler. The lower efficiency of pellet heaters compared to oil or gas heaters increases the primary energy demand. Consequently heat losses of the various systems have been studied. The systems have been modeled in TRNSYS and simulated with parameters identified from measurements. For almost all systems the flue gas losses are the main heat losses except for system 3 where store heat losses prevail. Relevant are also the heat losses of the burner and the boiler to the ambient. Significant leakage losses are noticed for system 3 and 4. For buildings with an open internal design system 1 is the most efficient solution. Other buildings should preferably apply system 3. The right choice of the system depends also on whether the heater is placed inside or outside of the heated are. A large potential for system optimization exist for all studied systems, which when applied could alter the relative merits of the different system types.

On statistical bounds of heuristic solutions to location problems

Solutions to combinatorial optimization problems, such as problems of locating facilities, frequently rely on heuristics to minimize the objective function. The optimum is sought iteratively and a criterion is needed to decide when the procedure (almost) attains it. Pre-setting the number of iterations dominates in OR applications, which implies that the quality of the solution cannot be ascertained. A small, almost dormant, branch of the literature suggests using statistical principles to estimate the minimum and its bounds as a tool to decide upon stopping and evaluating the quality of the solution. In this paper we examine the functioning of statistical bounds obtained from four different estimators by using simulated annealing on p-median test problems taken from Beasley’s OR-library. We find the Weibull estimator and the 2nd order Jackknife estimator preferable and the requirement of sample size to be about 10 being much less than the current recommendation. However, reliable statistical bounds are found to depend critically on a sample of heuristic solutions of high quality and we give a simple statistic useful for checking the quality. We end the paper with an illustration on using statistical bounds in a problem of locating some 70 distribution centers of the Swedish Post in one Swedish region. 

Confidence in heuristic solutions?

Solutions to combinatorial optimization problems frequently rely on heuristics to minimize an objective function. The optimum is sought iteratively and pre-setting the number of iterations dominates in operations research applications, which implies that the quality of the solution cannot be ascertained. Deterministic bounds offer a mean of ascertaining the quality, but such bounds are available for only a limited number of heuristics and the length of the interval may be difficult to control in an application. A small, almost dormant, branch of the literature suggests using statistical principles to derive statistical bounds for the optimum. We discuss alternative approaches to derive statistical bounds. We also assess their performance by testing them on 40 test p-median problems on facility location, taken from Beasley’s OR-library, for which the optimum is known. We consider three popular heuristics for solving such location problems; simulated annealing, vertex substitution, and Lagrangian relaxation where only the last offers deterministic bounds. Moreover, we illustrate statistical bounds in the location of 71 regional delivery points of the Swedish Post. We find statistical bounds reliable and much more efficient than deterministic bounds provided that the heuristic solutions are sampled close to the optimum. Statistical bounds are also found computationally affordable.

Natthärbärget som vandrande lösning

The shelter as a recurrent solution to homelessness During most of the 20th century shelters for the homeless has been criticized as being of too low standard and an unworthy way of living in a welfare society. During the 1960s and 1970s most shelters in Sweden were shut down and replaced with other forms of housing for the homeless. Since the late 1980s and early 1990s the issue of homelessness has returned to the political agenda as an existing social problem in Sweden. In this period we have also experienced a return of the shelters. These newly opened shelters are in many ways based on the same ideas like the old shelters described in stories of poverty and deprivation from the 19th century. In our article we raise the question how a system that has been rejected and condemned from both ethical and ideological standpoints as an unworthy way of living can be “remodernized” and considered again as a (temporary) solution to homelessness. We examine how shelters are justified in the 21st century and what functions they fill. We also discuss the fact that the shelters are almost exclusively run by (religious) voluntary organizations.

Network density and the p-median solution

The p-medianmodel is commonly used to find optimal locations of facilities for geographically distributed demands. So far, there are few studies that have considered the importance of the road network in the model. However, Han, Håkansson, and Rebreyend (2013) examined the solutions of the p-median model with densities of the road network varying from 500 to 70,000 nodes. They found as the density went beyond some 10,000 nodes, solutions have no further improvements but gradually worsen. The aim of this study is to check their findings by using an alternative heuristic being vertex substitution, as a complement to their using simulated annealing. We reject the findings in Han et al (2013). The solutions do not further improve as the nodes exceed 10,000, but neither do the solutions deteriorate.

Portals for microenterprises in rural area : two cases

Research has shown that microenterprises have ability to survive and grow with the support of portals that include eCcommerce. However, almost no research has demonstrated how it’s done and what support microenterprises want. Results of our study shows that the portals have to be improved to support the use of advanced ICT applications, make it usable to use, and give more time for core business for the participating microenterprises. We have seen that portals have to solve problem with the technical solution and the process of payment. The network building activities in the portals do not happen in such extent that we have expected based on previous research. If portals will get businesses to grow in microenterprises, we propose that in addition to providing access to advanced ICT applications need to climbs one step higher in the DTI ladder and create more of eCommerce to increase sales in a greater market. We also propose that portals which support cooperation between microenterprises in rural areas from different branches have the best chances to succeed in the future.