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Algorithms for a Partially Regularized Least Squares ProblemSkoglund, Ingegerd January 2007 (has links)
<p>Vid analys av vattenprover tagna från t.ex. ett vattendrag betäms halten av olika ämnen. Dessa halter är ofta beroende av vattenföringen. Det är av intresse att ta reda på om observerade förändringar i halterna beror på naturliga variationer eller är orsakade av andra faktorer. För att undersöka detta har föreslagits en statistisk tidsseriemodell som innehåller okända parametrar. Modellen anpassas till uppmätta data vilket leder till ett underbestämt ekvationssystem. I avhandlingen studeras bl.a. olika sätt att säkerställa en unik och rimlig lösning. Grundidén är att införa vissa tilläggsvillkor på de sökta parametrarna. I den studerade modellen kan man t.ex. kräva att vissa parametrar inte varierar kraftigt med tiden men tillåter årstidsvariationer. Det görs genom att dessa parametrar i modellen regulariseras.</p><p>Detta ger upphov till ett minsta kvadratproblem med en eller två regulariseringsparametrar. I och med att inte alla ingående parametrar regulariseras får vi dessutom ett partiellt regulariserat minsta kvadratproblem. I allmänhet känner man inte värden på regulariseringsparametrarna utan problemet kan behöva lösas med flera olika värden på dessa för att få en rimlig lösning. I avhandlingen studeras hur detta problem kan lösas numeriskt med i huvudsak två olika metoder, en iterativ och en direkt metod. Dessutom studeras några sätt att bestämma lämpliga värden på regulariseringsparametrarna.</p><p>I en iterativ lösningsmetod förbättras stegvis en given begynnelseapproximation tills ett lämpligt valt stoppkriterium blir uppfyllt. Vi använder här konjugerade gradientmetoden med speciellt konstruerade prekonditionerare. Antalet iterationer som krävs för att lösa problemet utan prekonditionering och med prekonditionering jämförs både teoretiskt och praktiskt. Metoden undersöks här endast med samma värde på de två regulariseringsparametrarna.</p><p>I den direkta metoden används QR-faktorisering för att lösa minsta kvadratproblemet. Idén är att först utföra de beräkningar som kan göras oberoende av regulariseringsparametrarna samtidigt som hänsyn tas till problemets speciella struktur.</p><p>För att bestämma värden på regulariseringsparametrarna generaliseras Reinsch’s etod till fallet med två parametrar. Även generaliserad korsvalidering och en mindre beräkningstung Monte Carlo-metod undersöks.</p> / <p>Statistical analysis of data from rivers deals with time series which are dependent, e.g., on climatic and seasonal factors. For example, it is a well-known fact that the load of substances in rivers can be strongly dependent on the runoff. It is of interest to find out whether observed changes in riverine loads are due only to natural variation or caused by other factors. Semi-parametric models have been proposed for estimation of time-varying linear relationships between runoff and riverine loads of substances. The aim of this work is to study some numerical methods for solving the linear least squares problem which arises.</p><p>The model gives a linear system of the form <em>A</em><em>1x1</em><em> + A</em><em>2x2</em><em> + n = b</em><em>1</em>. The vector <em>n</em> consists of identically distributed random variables all with mean zero. The unknowns, <em>x,</em> are split into two groups, <em>x</em><em>1</em><em> </em>and <em>x</em><em>2</em><em>.</em> In this model, usually there are more unknowns than observations and the resulting linear system is most often consistent having an infinite number of solutions. Hence some constraint on the parameter vector x is needed. One possibility is to avoid rapid variation in, e.g., the parameters<em> x</em><em>2</em><em>.</em> This can be accomplished by regularizing using a matrix <em>A</em><em>3</em>, which is a discretization of some norm. The problem is formulated</p><p>as a partially regularized least squares problem with one or two regularization parameters. The parameter <em>x</em><em>2</em> has here a two-dimensional structure. By using two different regularization parameters it is possible to regularize separately in each dimension.</p><p>We first study (for the case of one parameter only) the conjugate gradient method for solution of the problem. To improve rate of convergence blockpreconditioners of Schur complement type are suggested, analyzed and tested. Also a direct solution method based on QR decomposition is studied. The idea is to first perform operations independent of the values of the regularization parameters. Here we utilize the special block-structure of the problem. We further discuss the choice of regularization parameters and generalize in particular Reinsch’s method to the case with two parameters. Finally the cross-validation technique is treated. Here also a Monte Carlo method is used by which an approximation to the generalized cross-validation function can be computed efficiently.</p>
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Institutionella förutsättningar för långsiktig ekonomisk välfärd : en empirisk undersökning av institutionernas roll i tillväxttteorinLarsson, Johan January 2006 (has links)
<p>Jag använder ett från Världsbanken nyligen utkommet datamaterial över institutionell kvalitet i världens länder för att i en replikeringsstudie undersöka sambandet mellan institutionell utveckling och ekonomisk tillväxt. Modellen har med framgång redan tidigare använts, men i detta arbete är tidsperioden en senare och datamaterialet enligt min bedömning av högre kvalitet. För att kunna göra det senare uttalandet och analysera resultaten på ett uttömmande sätt, innefattar arbetet en översiktlig presentation av institutionella teorier. Eftersom undersökt samband i utgångsläget antas uppvisa dubbelriktad kausalitet, använder jag ett ekonometriskt tillvägagångssätt innehållande instrumentering för att trygga validiteten. Sammantaget visar resultaten en enkelriktad, positiv kausaleffekt från institutionell kvalitet till ekonomisk tillväxt. Det är en bit kvar till en verkligt fruktbar modellkonstruktion, samtidigt som arbetet pekar på att institutioner hör hemma i en sådan.</p>
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Planktivorous Auklets (Aethia pusilla and A. cristatella) nesting on St. Lawrence Island, Alaska as indicators of marine conditions in the northern Bering SeaGall, Adrian 22 March 2004 (has links)
Monitoring reproductive success, prey species composition, and colony size of
marine birds has been proposed as a method of assessing changes in marine
systems that are otherwise difficult to sample (Cairns 1987). I measured inter-annual
and intra-seasonal variability in reproductive parameters, taxonomic
composition of the diet, and adult body condition of Crested Auklets (Aethia
cristatella) and Least Auklets (A. pusilla) at 2 colonies near the village of Savoonga,
St. Lawrence Island, Alaska during the 2000-2002 breeding seasons to evaluate how
reproductive success of planktivorous seabirds is related to diet. I also assessed the
utility of two methods of population monitoring (surface counts and mark-resighting)
for detecting annual changes in breeding populations of Crested and Least auklets
during the 2001 and 2002 breeding seasons on the Kitnik colony.
Average reproductive success was generally high (>60% of nests) for both
auklet species during the 3 years of the study, but differed among years. Median
hatching dates for both species were 2 weeks earlier in the year of highest
reproductive success (2002), compared to the previous 2 years. In all 3 years, the
diet of Crested Auklets was predominantly euphausiids, while the diet of Least
Auklets consisted primarily of calanoid copepods, but species composition of the diet
differed among years for both species. Crested and Least auklets consumed more of
the large, lipid-rich copepod Neocalanus cristatus in 2002 than in the other 2 years
of the study. The year of lowest reproductive success (2001) was associated with
low prevalence of euphausiids in Crested Auklet diets late in the chick-rearing period
and high prevalence of the small, low-lipid copepod Calanus marshallae in Least
Auklet diets.
I observed an increase in total body mass of Crested Auklets during the 2002
breeding season, whereas total body mass declined through the breeding season in
the other 2 years. Seasonal changes in adult body mass of Crested Auklets may,
therefore, be a useful indicator of food availability. Average body mass of Least
Auklets declined in all 3 years, but was lowest in 2001, suggesting that low adult
body mass of Least Auklets may reflect poor foraging conditions. Fat reserves of
breeding auklets during egg-laying were not highly variable among or within breeding
seasons and therefore were not a sensitive predictor of subsequent breeding
success.
Counts of Crested Auklets in plots on the colony surface were highest in areas
of large average boulder size; Least Auklet surface counts were not as variable
among plots. Maximum counts of both species of auklets in plots did not differ
between years. Patterns of colony surface attendance during the breeding season,
however, did differ between years. The colony surface attendance of both auklet
species after hatching was higher in the year of high reproductive success.
Preventing nest initiation by covering plots with tarps did not reduce subsequent
colony surface attendance during chick-rearing (after the tarps were removed) for
either species, suggesting that reproductive success, independent of differences in
food availability, did not cause a difference in colony surface attendance. I estimated
abundance of Least Auklets nesting in two 100-m�� plots using mark-resight methods.
I concluded that surface counts may provide an indication of among-year differences
in colony attendance, but underestimate the number of breeding individuals by a
factor of 10. Mark-resighting techniques show more promise for detecting changes
in the number of breeding pairs. Reproductive success, adult body mass, and post-hatch
colony attendance of Crested and Least auklets appear positively associated
with zooplankton availability, particularly the prevalence of N. cristatus in the diet.
Annual monitoring of these 3 parameters, together with diet composition, are
important for understanding how both natural and anthropogenic climate change
may affect trophic structure of the northern Bering Sea ecosystem. / Graduation date: 2004
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Multiobject tracking by adaptive hypothesis testingJanuary 1979 (has links)
by Kenneth M. Keverian, Nils R. Sandell, Jr. / Office of Naval Research Contract ONR/N00014-77-C-0532 (85552). / Originally presented as the first author's thesis, (B.S.) in the M.I.T. Dept. of Electrical Engineering and Computer Science, 1979. / Bibliography: p. 114-115.
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Event compression using recursive least squares signal processingJanuary 1980 (has links)
Webster Pope Dove. / Originally published as thesis (Dept. of Electrical Engineering and Computer Science, M.S., 1980). / Bibliography: leaf 150. / National Science Foundation Grant ENG76-24117 National Science Foundation Grant ECS79-15226
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Least-squares variational principles and the finite element method: theory, formulations, and models for solid and fluid mechanicsPontaza, Juan Pablo 30 September 2004 (has links)
We consider the application of least-squares variational principles and the finite element method to the numerical solution of boundary value problems arising in the fields of solidand fluidmechanics.For manyof these problems least-squares principles offer many theoretical and computational advantages in the implementation of the corresponding finite element model that are not present in the traditional weak form Galerkin finite element model.Most notably, the use of least-squares principles leads to a variational unconstrained minimization problem where stability conditions such as inf-sup conditions (typically arising in mixed methods using weak form Galerkin finite element formulations) never arise. In addition, the least-squares based finite elementmodelalways yields a discrete system ofequations witha symmetric positive definite coeffcientmatrix.These attributes, amongst manyothers highlightedand detailed in this work, allow the developmentofrobust andeffcient finite elementmodels for problems of practical importance. The research documented herein encompasses least-squares based formulations for incompressible and compressible viscous fluid flow, the bending of thin and thick plates, and for the analysis of shear-deformable shell structures.
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A study of factors leading to growth in small firms. An examination of factors that impact on growth of small manufacturing in Least Developed Countries: The case of Ghana.Owusu, Kwame January 2007 (has links)
The focus of this study is to examine the factors that lead to growth in
small firms in a Least Developed Country (LDC). The research is
based on the manufacturing sector in Ghana. The main objectives of
the research are to identify the key variables that lead to small firms'
growth and to ascertain the critical barriers that impede growth.
A research model which is developed out of an initial exploratory
research and existing literature focuses on how the characteristics of
the owner/manager, the characteristics of the firm and the business
strategy variables interact to affect growth in employment. In addition
factors that are perceived to have constrained the growth of the small
firms during the study period are ascertained and discussed.
To properly test the hypotheses developed a face to face interview
survey involving 122 owner/managers of small manufacturing firms is
conducted. This resulted in a range of variables that allowed for the
construction of a comprehensive multivariate model of small firm
growth.
A resulting regression model provides about 68 percent of the
explanation for the growth of the small firms sampled. It also indicates
that the owner/manager characteristics variables offer the most
powerful explanation to small firm growth. We find that the
owner/manager's growth aspiration is the most influential factor in
achieving growth. The other owner/manager characteristics variables
that have positive influence on growth are level of education, prior
industry experience and entrepreneurial family background.
Owner/managers with local experience and/or with other business
interests are less likely to achieve faster growth. Foreign
owned/managed firms grow faster.
Younger and smaller firms appear to grow faster. While firms with
multiple ownerships tend to grow at a slower rate than firms owned and
managed by one person.
Business planning, marketing and export have positive and significant
impacts on growth. Other business strategies such as innovations and
staff training also have direct relationships with growth but not
significant.
Some of the main constraining factors to growth are cost of borrowing,
lack of access to credit, high cost of inputs, lack of trust within the
business community, high bureaucracy, late payments and lack of
efficient support system. While the external environment plays
important role in small firm growth and development, the behaviours,
response and strategies pursued by individual owner/manager are
significant factors that determine the rate at which a firm will grow. / Ghana Leasing Company Limited
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Estimation in partly parametric additive Cox modelsLäuter, Henning January 2003 (has links)
The dependence between survival times and covariates is described e.g. by proportional hazard models. We consider partly parametric Cox models and discuss here the estimation of interesting parameters. We represent the ma- ximum likelihood approach and extend the results of Huang (1999) from linear to nonlinear parameters. Then we investigate the least squares esti- mation and formulate conditions for the a.s. boundedness and consistency of these estimators.
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Algorithms for a Partially Regularized Least Squares ProblemSkoglund, Ingegerd January 2007 (has links)
Vid analys av vattenprover tagna från t.ex. ett vattendrag betäms halten av olika ämnen. Dessa halter är ofta beroende av vattenföringen. Det är av intresse att ta reda på om observerade förändringar i halterna beror på naturliga variationer eller är orsakade av andra faktorer. För att undersöka detta har föreslagits en statistisk tidsseriemodell som innehåller okända parametrar. Modellen anpassas till uppmätta data vilket leder till ett underbestämt ekvationssystem. I avhandlingen studeras bl.a. olika sätt att säkerställa en unik och rimlig lösning. Grundidén är att införa vissa tilläggsvillkor på de sökta parametrarna. I den studerade modellen kan man t.ex. kräva att vissa parametrar inte varierar kraftigt med tiden men tillåter årstidsvariationer. Det görs genom att dessa parametrar i modellen regulariseras. Detta ger upphov till ett minsta kvadratproblem med en eller två regulariseringsparametrar. I och med att inte alla ingående parametrar regulariseras får vi dessutom ett partiellt regulariserat minsta kvadratproblem. I allmänhet känner man inte värden på regulariseringsparametrarna utan problemet kan behöva lösas med flera olika värden på dessa för att få en rimlig lösning. I avhandlingen studeras hur detta problem kan lösas numeriskt med i huvudsak två olika metoder, en iterativ och en direkt metod. Dessutom studeras några sätt att bestämma lämpliga värden på regulariseringsparametrarna. I en iterativ lösningsmetod förbättras stegvis en given begynnelseapproximation tills ett lämpligt valt stoppkriterium blir uppfyllt. Vi använder här konjugerade gradientmetoden med speciellt konstruerade prekonditionerare. Antalet iterationer som krävs för att lösa problemet utan prekonditionering och med prekonditionering jämförs både teoretiskt och praktiskt. Metoden undersöks här endast med samma värde på de två regulariseringsparametrarna. I den direkta metoden används QR-faktorisering för att lösa minsta kvadratproblemet. Idén är att först utföra de beräkningar som kan göras oberoende av regulariseringsparametrarna samtidigt som hänsyn tas till problemets speciella struktur. För att bestämma värden på regulariseringsparametrarna generaliseras Reinsch’s etod till fallet med två parametrar. Även generaliserad korsvalidering och en mindre beräkningstung Monte Carlo-metod undersöks. / Statistical analysis of data from rivers deals with time series which are dependent, e.g., on climatic and seasonal factors. For example, it is a well-known fact that the load of substances in rivers can be strongly dependent on the runoff. It is of interest to find out whether observed changes in riverine loads are due only to natural variation or caused by other factors. Semi-parametric models have been proposed for estimation of time-varying linear relationships between runoff and riverine loads of substances. The aim of this work is to study some numerical methods for solving the linear least squares problem which arises. The model gives a linear system of the form A1x1 + A2x2 + n = b1. The vector n consists of identically distributed random variables all with mean zero. The unknowns, x, are split into two groups, x1 and x2. In this model, usually there are more unknowns than observations and the resulting linear system is most often consistent having an infinite number of solutions. Hence some constraint on the parameter vector x is needed. One possibility is to avoid rapid variation in, e.g., the parameters x2. This can be accomplished by regularizing using a matrix A3, which is a discretization of some norm. The problem is formulated as a partially regularized least squares problem with one or two regularization parameters. The parameter x2 has here a two-dimensional structure. By using two different regularization parameters it is possible to regularize separately in each dimension. We first study (for the case of one parameter only) the conjugate gradient method for solution of the problem. To improve rate of convergence blockpreconditioners of Schur complement type are suggested, analyzed and tested. Also a direct solution method based on QR decomposition is studied. The idea is to first perform operations independent of the values of the regularization parameters. Here we utilize the special block-structure of the problem. We further discuss the choice of regularization parameters and generalize in particular Reinsch’s method to the case with two parameters. Finally the cross-validation technique is treated. Here also a Monte Carlo method is used by which an approximation to the generalized cross-validation function can be computed efficiently.
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Acoustic Emission in Composite Laminates - Numerical Simulations and Experimental CharacterizationJohnson, Mikael January 2002 (has links)
No description available.
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