Browsing by Author "Ehtamo, Harri"

Now showing 1 - 20 of 172
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    Accelerated Testing in Product Development
    (2000) Oksanen, Olli-Matti; Grayeff, Michael; Takala, Petri; Teknillisen fysiikan ja matematiikan osasto; Teknillinen korkeakoulu; Helsinki University of Technology; Ehtamo, Harri
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    An Accessibility-Based Simulation Model for Destination and Mode Choice of Trips
    (2011) Salomaa, Osmo; Moilanen, Paavo; Pesonen, Hannu; Matematiikan ja systeemianalyysin laitos; Perustieteiden korkeakoulu; School of Science; Ehtamo, Harri
    Transportation models are needed to assess the impact of planned transportation and land use projects and operations. Models currently in use are to a large extent outdated and theoretically problematic and are poorly applicable to many current problems. The goal of this work is to develop a new kind of transportation model, one that takes trip chains into account, includes a time-dimension and in which ordinary daily trips and related decision-making is handled by simulation. The model is implemented for the Helsinki commuting area using the spatial precision of a regular 250 meter grid. The main purpose of the model is to investigate how changes in land use and transportation system affect traveling. Results from the model are examined for the present day and for the forecasted year 2035 according to a draft of the 2011 Helsinki region transport system plan. According to the results, the model looks promising and its strengths and limitations have been identified for further development and use. The model is applicable in the short term especially for applications that require spatial precision or inclusion of pedestrian and bicycle trips in analysis and in the long term it can be considered a possible candidate to replace traditional aggregate models.
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    Adjustment of affine equations in equilibrium analysis
    (2005) Kitti, Mitri; Teknillisen fysiikan ja matematiikan osasto; Teknillinen korkeakoulu; Helsinki University of Technology; Ehtamo, Harri
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    Algorithms for Variational Learning of Mixture of Gaussians
    (2009) Kuusela, Mikael; Raiko, Tapani; Informaatio- ja luonnontieteiden tiedekunta; Ehtamo, Harri
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    Alueellisten erojen tutkiminen pienen pienten keskosten syntyvyydessä ja kustannuksissa
    (2015-07-25) Siitonen, Susanna; Ehtamo, Harri; Perustieteiden korkeakoulu; Ehtamo, Harri
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    Analysing optimal routing of single elevator
    (2011) Luukkonen, Teppo; Ruokokoski, Mirko; Perustieteiden korkeakoulu; Ehtamo, Harri
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    Analysis of a predator-prey system with a shared disease
    (2014) Lindqvist, Lasse Kristian; Kisdi, Eva; Perustieteiden korkeakoulu; Perustieteiden korkeakoulu; Ehtamo, Harri
    This thesis studies a predator-prey model with a shared disease. In addition to the prey the predator has an alternative food source which it consumes. Both species are vulnerable to a pathogen that spreads not only from prey to prey but also from predator to predator. Predators can get infected when consuming infected preys and preys can get infected from environmental transmission. Properties of the model and its behaviour are studied. This includes the basic reproduction, the nextgeneration matrix and the stability of equilibria. Factors affecting the properties of the equilibria are identified. Consumption rate, the rate at which the predator consumes prey with, is studied and critical consumption rate, where prey or predator population ceases to exist, is identified. Evolution of the consumpion rate is studied within the adaptive dynamics framework. Without the presence of the pathogen the consumption rate increases indefinitely, but introducing the pathogen to the system can change the course of evolution and make a decrease in the consumption rate possible. The evolution of the consumption rate is explored further with help of trade-offs. Taking into account that increase in consumption rate might be costly to the predator provides alternative outcomes. Two trade-offs that are studied are trade-off between consumption rate and the consumption of the alternative food source and trade-off between consumption and death rate. These trade-offs can exist concurrently or independently. Having both of the trade-offs in place we can identify situations where we have a branching point. In such a situation the consumption rate evolves first to this brancing point, where two different branches arise and disruptive evolution takes place. The result is two different types of predator, one using only the alternative food source and one using only the prey as its source of food.
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    Analyzing vibration sources based on their responses in a large cruise ship
    (2005) Tenovuo, Karno; Rautaheimo, Patrik; Matusiak, Jerzy; Automaatio- ja systeemitekniikan osasto; Teknillinen korkeakoulu; Helsinki University of Technology; Ehtamo, Harri
    Tutkimuksen tavoitteena on etsiä herätteiden ja vasteiden väliset riippuvuussuhteet isojen risteilylaivojen runkovärähtelyissä. Erityisesti tutkitaan ympäristötekijöiden aiheuttamien herätteiden ja niiden aiheuttamien vasteiden välisiä riippuvuussuhteita rungon ensimmäisille ominaistaajuuksille. Diplomityössä kehitetään erilaisia analysointitapoja värähtelyjen selvittämiseksi ja menetelmä, jolla voidaan arvioida vasteiden avulla herätteen paikka ja tyyppi. Laivojen koko kasvaa vuosi vuodelta ja samalla kasvavat niiltä vaaditut ominaisuudet. Koon kasvaminen saattaa johtaa tiettyjen rakenteiden ja alueiden altistumiseen matalataajuiselle värähtelylle, joka taas puolestaan lisää rungon rasitusta ja vähentää matkustajien mukavuutta. Värähtelyherätteestä tulisi tietää tulevaisuudessa enemmän, jotta runko voitaisiin suunnitella optimaalisesti pienentämään värähtelytasoja. Tavoitteiden saavuttamiseksi tutkittiin useita erilaisia tapoja analysoida herätettä ja vastetta. Nämä tavat perustuvat mm. korrelaatiolaskentaan perustuvaan herätteen paikan selvittämiseen, spektraalianalyysiin, regressiolaskentaan sekä Simulinksimulointimallin käyttöön. Työssä kehitetyt menetelmät vasteen analysointiin sisältävät jonkin verran epävarmuutta, mutta antavat kuitenkin selkeän kuvan herätteen tyypistä, paikasta ja voima4uudesta. Simulointimallilla pystyttiin muodostamaan selkeä käsitys herätteiden ja vasteiden välisistä yhteyksistä. Työssä kehitettiin monta pidemmän aikavälin värähtelytietojen esitystekniikkaa, jotka paljastavat värähtelyn luonteesta erilaisia asioita, kuten värähtelyn hallitsevat taajuudet ja ihmisten tuntemat värähtelytasot.
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    Anatomical connectivity networks of the human brain
    (2015-10-05) Asikainen, Milja; Saramäki, Jari; Systeemitieteet; Perustieteiden korkeakoulu; Ehtamo, Harri
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    Asiakaspalautteen monikanavainen keräys ja analyysi
    (2014-03-26) Räty, Petteri; Ehtamo, Harri; Perustieteiden korkeakoulu; Ehtamo, Harri
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    Assessing the effects of entrepreneurial orientation in Finnish software industry
    (2009) Ylitalo, Jukka; Rönkkö, Mikko; Informaatio- ja luonnontieteiden tiedekunta; Ehtamo, Harri
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    Bayesian Games for Analysis of Asymmetric Warfare Tactics
    (2011) Eskola, Olli; Rosqvist, Tony; Matematiikan ja systeemianalyysin laitos; Perustieteiden korkeakoulu; School of Science; Ehtamo, Harri
    Roadside bombs have caused more than half of the casualties of the U.S. troops in Afghan war. The aim of this work is to examine the threats of the modern asymmetric warfare and to develop operations research based methods for advanced threat preparation. The main emphasis is on the roadside bombs. In this work, we are investigating the conflict between two forces. We define an influence diagram that contains the events relevant after the initialization of the bomb. The social support of the local people is included in the model because it is a key factor in asymmetric warfare. Following Bayesian game theory, both forces have two types and the types define the tactics of the forces. The types are given either as a joint common probability distribution or as subjective conditional probabilities. For the conditional probabilities, a theorem is formulated to define when they are mutually consistent. When the conditional probabilities are consistent, the common joint distribution can be calculated using the Bayes rule. When the subjective probabilities are mutually inconsistent, the Kullback-Leibner divergence measure is used for calculating the common joint probability distribution that is closest in terms of this measure, given the subjective probabilities. An algorithm solving the Bayesian Nash Equilibrium of the normal form game is programmed. The equilibrium shows the best response, i.e. the tactics adopted by players maximizing expected utility. By assumption, the utilities sum up to constant. The influence diagram combined with carefully elicited expert judgments provides a systematic approach for modeling the existing uncertainties related to the outcomes of the applied tactics. Several computational cases are examined. Based on these, the social support, for example, is more significant than the type probabilities of the forces.
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    Best-Response-ovenvalinta-algoritmin toiminnan tutkiminen kokeellisen aineiston avulla
    (2010) Punakallio, Perttu; Heliövaara, Simo; Informaatio- ja luonnontieteiden tiedekunta; Ehtamo, Harri
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    Blocking in Third Generation Radio Access Networks
    (2000) Pöysti, Aku; Teknillisen fysiikan ja matematiikan osasto; Teknillinen korkeakoulu; Helsinki University of Technology; Ehtamo, Harri
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    Cellular Automaton Evacuation Model Coupled with a Spatial Game
    (2014) von Schantz, Anton; Ehtamo, Harri; Department of Mathematics and Systems Analysis; Slezak, Dominik; Schaefer, Gerald; Vuong, Son T.; Kim, Yoo-Sung
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    Classifying Individual-Level Migration Behavior Using Multivariate Methods
    (2010) Mangs, Karl Johan; Röytiö, Petri; Matematiikan ja systeemianalyysin laitos; Perustieteiden korkeakoulu; School of Science; Ehtamo, Harri
    The decision to migrate tends to be coupled with significant changes in the migrant's personal life. Consequently, the ability to forecast which individuals are about to migrate would offer companies an excellent opportunity to benefit from this fact in their prospecting and marketing. Targeting imminent migrants with well-timed and suitable offers would yield higher readership levels due to the more interested prospects. The aim of this thesis was to develop a method for classifying the adult Finnish population into one of the following categories: those who will migrate within the following six months, and those who will migrate at a later date. Utilizing the k-nearest neighbour algorithm, generalized linear models, support vector machines, optimally-pruned extreme learning machines, and their ensembles this thesis sought to analyze which approach offers the best classification result and whether there are significant differences regarding the practical implementations of these methods. Provided access to the full extent of the Population Information System database, this thesis was offered a premium opportunity to model the Finnish migration phenomenon through a large sample size and an extensive set of features. On the other hand, this created a demand for feature selection, which in this thesis was conducted based on a literature review. Moreover, the Delta Test was implemented as a method for pruning the selected shortlist from additional redundant features. The results revealed that there exists a subset of features that have a substantial impact on the classification accuracy. In addition, it was concluded that all of the implemented methods were capable of producing satisfactory results and that their performances were rather similar. However, considering that this thesis was able to highlight some very distinct practical differences regarding the methods, these findings provide valuable insights concerning future implementations.
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    Competition-Based Dynamic Pricing in E-Commerce
    (2019-12-17) Aalto, Henrik; Saarinen, Erkka; Perustieteiden korkeakoulu; Ehtamo, Harri
    E-commerce is a fascinating field of retail. It offers numerous advantages for retailers starting from widely reachable customers, easily changeable assortments, and reduced fixed costs. On the other hand, e-commerce accelerates competition. For a consumer it is merely a matter of some clicks to switch from one online store to another offering the same item with faster shipping or lower price. The goal of this study is to find and evaluate a method to dynamically reprice durable goods over an infinite horizon in an online store based on competitor prices for the same products. To provide support for the method, we first model the daily sales quantities with a zero-inflated binomial regression. Then, we build a myopically optimal pricing method on top of the demand model. The performance of the model is assessed by simulations with two different scenarios, one assuming competitors would not react and another assuming one of them starts a price war. In both the scenarios, our pricing method is able to perform well with up to 20 percent increase in gross margin compared to current pricing. Last, we conduct a case study by repricing a group of products in an online store for a month with our method. Due to large variances in sales and a small test group, no statistically sound conclusions can be made. However, the performance of our method is roughly equal to the current pricing policies. Thus, one could conduct a larger and longer test to gain more information. The key findings in our study are as follows. First, even rather simple pricing methods should outperform any static pricing rules. Second, having competitor price information available in e-commerce is crucial as the difference to competitors matters more than the price point itself. Third, detecting changes from the sales of slowly moving goods would require huge sample sizes and thus performances of pricing methods should be assessed with products with higher demands.
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    Computation of Incentive Stackelberg Solution
    (2000) Kitti, Mitri; Ehtamo, Harri; Tuotantotalouden osasto; Teknillinen korkeakoulu; Helsinki University of Technology; Ehtamo, Harri
    Tässä työssä esitetään uusi menetelmä Stackelbergin pelin kannusteratkaisun laskemiseksi. Stackelbergin pelit ovat peliteoreettisia malleja päätöksentekotilanteille, joissa osapuolet, pelaajat, toimivat tietyssä järjestyksessä. Ensimmäisenä toimiva pelaaja on johtaja ja muut ovat seuraajia. Kannustepelissä johtaja voi sitoutua ratkaisuun, joka riippuu seuraajien päätöksistä. Tällaista strategiaa kutsutaan kannusteeksi. Johtajan pyrkimyksenä on ilmoittaa kannuste, joka saa seuraajat toimimaan hänen kannaltaan parhaalla tavalla. Työssä esitetään lineaarisen kannusteratkaisun laskemiseksi uusi menetelmä, joka perustuu epälineaarisen yhtälöryhmän numeeriseen ratkaisemiseen. Yksinkertaisin menetelmä yhtälöryhmän ratkaisemiseksi on kiintopisteiteraatio. Työssä osoitetaan, että kiintopisteiteraatio suppenee, kun yhtälöryhmä toteuttaa ehdot, jotka muistuttavat kansantaloustieteessä syntyvien hintakoordinointiyhtälöiden ominaisuuksia. Työssä tarkastellaan kahta numeerista esimerkkiä. Ensimmäinen Esimerkki on kahden pelaajan kannustepeli, jossa seuraajalla on neliöllinen kustannusfunktio. Toisessa esimerkissä on duopolimalli, jossa hallitus toimii johtajana ja seuraajina on kaksi kilpailevaa yritystä, jotka pelaavat keskenään Nash-tasapainostrategioita käyttäen. Numeeriset laskut ovat yksinkertaisten oppimisprosessien simulointeja. Toinen menetelmä, jota työssä on käytetty kannusteratkaisun laskemiseksi, on biologista evoluutiota jäljittelevä geneettinen algoritmi. Esimerkkilaskut osoittavat, että geneettisellä algoritmilla kannusteratkaisu löytyy nopeasti, mutta tarkan ratkaisun löytäminen vaatii enemmän laskentatyötä kuin kiintopisteiteraatio.
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    Computation of mixed-strategy equilibria in the repeated prisoner's dilemma
    (2015-12-16) Timonen, Juho; Berg, Kimmo; Perustieteiden korkeakoulu; Ehtamo, Harri
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    Computation under limited information in nonlinear pricing
    (2008) Berg, Kimmo; Ehtamo, Harri; Informaatio- ja luonnontieteiden tiedekunta; Teknillinen korkeakoulu; Helsinki University of Technology; Ehtamo, Harri