Search results for "Fitting"

Bayesian regularization for flexible baseline hazard functions in Cox survival models.

2019

Fully Bayesian methods for Cox models specify a model for the baseline hazard function. Parametric approaches generally provide monotone estimations. Semi-parametric choices allow for more flexible patterns but they can suffer from overfitting and instability. Regularization methods through prior distributions with correlated structures usually give reasonable answers to these types of situations. We discuss Bayesian regularization for Cox survival models defined via flexible baseline hazards specified by a mixture of piecewise constant functions and by a cubic B-spline function. For those "semi-parametric" proposals, different prior scenarios ranging from prior independence to particular c…

A Software Tool for the Exponential Power Distribution: The normalp Package

2005

In this paper we present the normalp package, a package for the statistical environment R that has a set of tools for dealing with the exponential power distribution. In this package there are functions to compute the density function, the distribution function and the quantiles from an exponential power distribution and to generate pseudo-random numbers from the same distribution. Moreover, methods concerning the estimation of the distribution parameters are described and implemented. It is also possible to estimate linear regression models when we assume the random errors distributed according to an exponential power distribution. A set of functions is designed to perform simulation studi…

Updating input–output matrices: assessing alternatives through simulation

2009

A problem that frequently arises in economics, demography, statistics, transportation planning and stochastic modelling is how to adjust the entries of a matrix to fulfil row and column aggregation constraints. Biproportional methods in general and the so-called RAS algorithm in particular, have been used for decades to find solutions to this type of problem. Although alternatives exist, the RAS algorithm and its extensions are still the most popular. Apart from some interesting empirical and theoretical properties, tradition, simplicity and very low computational costs are among the reasons behind the great success of RAS. Nowadays computer hardware and software have made alternative proce…

2015

Abstract. In X-ray computed microtomography (μXCT) image processing is the most important operation prior to image analysis. Such processing mainly involves artefact reduction and image segmentation. We propose a new two-stage post-reconstruction procedure of an image of a geological rock core obtained by polychromatic cone-beam μXCT technology. In the first stage, the beam-hardening (BH) is removed applying a best-fit quadratic surface algorithm to a given image data set (reconstructed slice), which minimizes the BH offsets of the attenuation data points from that surface. The final BH-corrected image is extracted from the residual data, or the difference between the surface elevation valu…

Boolean operations with implicit and parametric representation of primitives using R-functions

2005

We present a new and efficient algorithm to accurately polygonize an implicit surface generated by multiple Boolean operations with globally deformed primitives. Our algorithm is special in the sense that it can be applied to objects with both an implicit and a parametric representation, such as superquadrics, supershapes, and Dupin cyclides. The input is a constructive solid geometry tree (CSG tree) that contains the Boolean operations, the parameters of the primitives, and the global deformations. At each node of the CSG tree, the implicit formulations of the subtrees are used to quickly determine the parts to be transmitted to the parent node, while the primitives' parametric definition …

A multi-methodology and sustainability-supporting framework for implementation and assessment of a holistic building renovation

La ristrutturazione degli edifici in futuro dovrà essere condotta secondo una prospettiva più olistica legata alla sostenibilità vista in una più ampia gamma di obiettivi/criteri e facilitata dagli scenari di ristrutturazione possibili. La ristrutturazione degli edifici dovrebbe servire a migliorarne le performance al fine di soddisfare le esigenze degli utenti, rendendo questi ultimi meno vulnerabili in relazione ai futuri costi energetici. Vi è un grande potenziale per ridurre il consumo di energia negli edifici esistenti. Tuttavia, ciò non deve comprometterè i valori architettonici e di qualità che rendono particolari. Pertanto, non possono essere semplicemente rinnovati, ma devono subir…

Characterization of the bulk flow properties of industrial powders from shear tests

2020

Bulk flow properties from shear analysis of compacted powders can be evaluated following different approaches. Experimental values of shear stresses obtained by conventional shear cells are traditionally used to build yield loci, from which the most relevant flow properties could be found. Such flow properties play an important role in determining their performance under fluidization conditions. In this work, a useful app, named cYield, was developed by using the new Matlab&rsquo

Increasing the Inference and Learning Speed of Tsetlin Machines with Clause Indexing

2020

The Tsetlin Machine (TM) is a machine learning algorithm founded on the classical Tsetlin Automaton (TA) and game theory. It further leverages frequent pattern mining and resource allocation principles to extract common patterns in the data, rather than relying on minimizing output error, which is prone to overfitting. Unlike the intertwined nature of pattern representation in neural networks, a TM decomposes problems into self-contained patterns, represented as conjunctive clauses. The clause outputs, in turn, are combined into a classification decision through summation and thresholding, akin to a logistic regression function, however, with binary weights and a unit step output function. …

Energy efficiency and CO2 emissions of port container terminal equipment: Evidence from the Port of Valencia

2019

Abstract Energy efficiency has emerged as a key point in port industry because of different factors such as the adoption of stronger environmental regulations and the increasing pressure of the local community on the surrounding ports. As gathering operational data from port terminals can be difficult due to privacy, studies on emissions and energy efficiency of these terminals are scarce. The following research provides key information about the real energy consumption and CO2 emissions of one of the most relevant container terminals in the Mediterranean area, located in Valencia, Spain. The results show that yard terminal tractors and rubber tyred gantry cranes (RTGs) are the main emissio…

The dynamic interactive pattern of assimilation and contrast: Accounting for standard extremity in comparative evaluations

2021

Abstract Social judgments are often influenced by comparison to some standard in the environment, either moving the judgment closer (assimilating) to or away (contrasting) from this standard. Which direction this effect will take depends heavily on the relative standing of these standards on the judgment dimension compared to the target of the judgment. In previous research, items and comparison standards were often selected arbitrarily, ignoring or simplifying their influence substantially. The current work takes a fine-grained holistic curve fitting approach to measure response patterns across a wide range of standard extremities, showing that a narrower approach can pose limits to the ge…