Number of found documents: 1656
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Application of the Infinitely Many Times Repeated BNS Update and Conjugate Directions to Limited-Memory Optimization Methods
Vlček, Jan; Lukšan, Ladislav
2019 - English
To improve the performance of the L-BFGS method for large scale unconstrained optimization, repeating of some BFGS updates was proposed. Since this can be time consuming, the extra updates need to be selected carefully. We show that groups of these updates can be repeated infinitely many times under some conditions, without a noticeable increase of the computational time. The limit update is a block BFGS update. It can be obtained by solving of some Lyapunov matrix equation whose order can be decreased by application of vector corrections for conjugacy. Global convergence of the proposed algorithm is established for convex and sufficiently smooth functions. Numerical results indicate the efficiency of the new method. Keywords: unconstrained minimization; limited-memory variable metric methods; the repeated Byrd-Nocedal-Schnabel update; the Lyapunov matrix equation; the conjugate directions; global convergence; numerical results Available at various institutes of the ASCR
Application of the Infinitely Many Times Repeated BNS Update and Conjugate Directions to Limited-Memory Optimization Methods

To improve the performance of the L-BFGS method for large scale unconstrained optimization, repeating of some BFGS updates was proposed. Since this can be time consuming, the extra updates need to be ...

Vlček, Jan; Lukšan, Ladislav
Ústav informatiky, 2019

Hybrid Methods for Nonlinear Least Squares Problems
Lukšan, Ladislav; Matonoha, Ctirad; Vlček, Jan
2019 - English
This contribution contains a description and analysis of effective methods for minimization of the nonlinear least squares function F(x) = (1=2)fT (x)f(x), where x ∈ Rn and f ∈ Rm, together with extensive computational tests and comparisons of the introduced methods. All hybrid methods are described in detail and their global convergence is proved in a unified way. Some proofs concerning trust region methods, which are difficult to find in the literature, are also added. In particular, the report contains an analysis of a new simple hybrid method with Jacobian corrections (Section 8) and an investigation of the simple hybrid method for sparse least squares problems proposed previously in [33] (Section 14). Keywords: numerical optimization; nonlinear least squares; trust region methods; hybrid methods; sparse problems; partially separable problems; numerical experiments Available in a digital repository NRGL
Hybrid Methods for Nonlinear Least Squares Problems

This contribution contains a description and analysis of effective methods for minimization of the nonlinear least squares function F(x) = (1=2)fT (x)f(x), where x ∈ Rn and f ∈ Rm, together with ...

Lukšan, Ladislav; Matonoha, Ctirad; Vlček, Jan
Ústav informatiky, 2019

Sort Program for Real Keys with Linear Time Complexity
Jiřina, Marcel
2019 - Czech
In this report we present a program for sorting data structures with sorting keys as real numbers, i.e. of type "real" or "float". The basis of the program is a modification of the countingsort algorithm for reals (instead of integers). It uses a comparision-type sorting for small part of data set given. The time complexity of this part of program can be bounded by linear function of n and thus, the total time complexity is also O(n) for n data items. Keywords: sorting; real sorting keys; counting sort Available in a digital repository NRGL
Sort Program for Real Keys with Linear Time Complexity

In this report we present a program for sorting data structures with sorting keys as real numbers, i.e. of type "real" or "float". The basis of the program is a modification of the countingsort ...

Jiřina, Marcel
Ústav informatiky, 2019

Does a Singular Symmetric Interval Matrix Contain a Symmetric Singular Matrix?
Rohn, Jiří
2019 - English
We consider the conjecture formulated in the title concerning existence of a symmetric singular matrix in a singular symmetric interval matrix. We show by means of a counterexample that it is generally not valid, and we prove that it becomes true under an additional assumption of positive semide niteness of the midpoint matrix. The proof is constructive. Keywords: symmetric interval matrix; singularity; positive semide niteness Available in a digital repository NRGL
Does a Singular Symmetric Interval Matrix Contain a Symmetric Singular Matrix?

We consider the conjecture formulated in the title concerning existence of a symmetric singular matrix in a singular symmetric interval matrix. We show by means of a counterexample that it is ...

Rohn, Jiří
Ústav informatiky, 2019

Transforming hierarchical images to program expressions using deep networks
Křen, Tomáš
2018 - English
We present a technique describing how to effectively train a neural network given an image to produce a formal description of the given image. The basic motivation of the proposed technique is an intention to design a new tool for automatic program synthesis capable of transforming sensory data (in our case static image, but generally a phenotype) to a formal code expression (i.e. syntactic tree of a program), such that the code (from evolutionary perspective a genotype) evaluates to a value that is similar to the input data, ideally identical. Our approach is partially based on our technique for generating program expressions in the context of typed functional genetic programming. We present promising results evaluating a simple image description language achieved with a deep network combining convolution encoder of images and recurrent decoder for generating program expressions in the sequential prefix notation and propose possible future applications. Keywords: deep networks; automatic program synthesis; image processing Available in a digital repository NRGL
Transforming hierarchical images to program expressions using deep networks

We present a technique describing how to effectively train a neural network given an image to produce a formal description of the given image. The basic motivation of the proposed technique is an ...

Křen, Tomáš
Ústav informatiky, 2018

Nonparametric Bootstrap Techniques for Implicitly Weighted Robust Estimators
Kalina, Jan
2018 - English
The paper is devoted to highly robust statistical estimators based on implicit weighting, which have a potential to find econometric applications. Two particular methods include a robust correlation coefficient based on the least weighted squares regression and the minimum weighted covariance determinant estimator, where the latter allows to estimate the mean and covariance matrix of multivariate data. New tools are proposed allowing to test hypotheses about these robust estimators or to estimate their variance. The techniques considered in the paper include resampling approaches with or without replacement, i.e. permutation tests, bootstrap variance estimation, and bootstrap confidence intervals. The performance of the newly described tools is illustrated on numerical examples. They reveal the suitability of the robust procedures also for non-contaminated data, as their confidence intervals are not much wider compared to those for standard maximum likelihood estimators. While resampling without replacement turns out to be more suitable for hypothesis testing, bootstrapping with replacement yields reliable confidence intervals but not corresponding hypothesis tests. Keywords: robust statistics; econometrics; correlation coefficient; multivariate data Fulltext is available at external website.
Nonparametric Bootstrap Techniques for Implicitly Weighted Robust Estimators

The paper is devoted to highly robust statistical estimators based on implicit weighting, which have a potential to find econometric applications. Two particular methods include a robust correlation ...

Kalina, Jan
Ústav informatiky, 2018

How to down-weight observations in robust regression: A metalearning study
Kalina, Jan; Pitra, Zbyněk
2018 - English
Metalearning is becoming an increasingly important methodology for extracting knowledge from a data base of available training data sets to a new (independent) data set. The concept of metalearning is becoming popular in statistical learning and there is an increasing number of metalearning applications also in the analysis of economic data sets. Still, not much attention has been paid to its limitations and disadvantages. For this purpose, we use various linear regression estimators (including highly robust ones) over a set of 30 data sets with economic background and perform a metalearning study over them as well as over the same data sets after an artificial contamination. We focus on comparing the prediction performance of the least weighted squares estimator with various weighting schemes. A broader spectrum of classification methods is applied and a support vector machine turns out to yield the best results. While results of a leave-1-out cross validation are very different from results of autovalidation, we realize that metalearning is highly unstable and its results should be interpreted with care. We also focus on discussing all possible limitations of the metalearning methodology in general. Keywords: metalearning; robust statistics; linear regression; outliers Available on request at various institutes of the ASCR
How to down-weight observations in robust regression: A metalearning study

Metalearning is becoming an increasingly important methodology for extracting knowledge from a data base of available training data sets to a new (independent) data set. The concept of metalearning is ...

Kalina, Jan; Pitra, Zbyněk
Ústav informatiky, 2018

Detailní simulace proudění, teplot a znečištění vzduchu pro oblast Praha-Dejvice
Resler, Jaroslav; Geletič, Jan; Krč, Pavel; Eben, Kryštof
2018 - Czech
Simulations of Prague quarter Dejvice were performed with newly developed urban climate model PALM-4U based on LES model PALM. The modelling domain has extent 1000 x 800 m and the resolution of the model was 2 m. Two 24 hours episodes were simulated. The summer episode was intended to assess mainly the UHI effects and the winter episode to assess mainly the air quality issues. Two variants were simulated - the current real situation and the scenario with considered new buildings in the area of Victory Square (Vítězné náměstí). Some comments of the ressults are appended at the end of the report. Keywords: PALM; LES; Urban Heat Island; Urban Air Quality; scenarios assessment Available in digital repository of the ASCR
Detailní simulace proudění, teplot a znečištění vzduchu pro oblast Praha-Dejvice

Simulations of Prague quarter Dejvice were performed with newly developed urban climate model PALM-4U based on LES model PALM. The modelling domain has extent 1000 x 800 m and the resolution of the ...

Resler, Jaroslav; Geletič, Jan; Krč, Pavel; Eben, Kryštof
Ústav informatiky, 2018

Datová sada pro detekci dezinformačního obsahu – případová studie Novičok v Česku
Řimnáč, Martin
2018 - Czech
Publikování dezinformací na webu hraje stále větší roli, proto vyvstává otázka, jak takovému obsahu čelit, a nebo na jeho potenciální závadnost alespoň upozornit. Propaganda využívá dezinformací k relativizaci skutečností, jejichž popis se snaží většinou nepřímo zpochybnit. Příspěvek formou případové studie v konkrétní kauze formálně popisuje výroky prezentované v článcích publikovaných na webu a to včetně účelu jejich publikování, všímá si některých zajímavých aspektů prezentovaných dezinformací a hledá model pro jejich popis. Cílem příspěvku je informovat o vznikající datové sadě a ilustrovat základní použité dezinformační techniky včetně důsledků jejich použití. The paper presents a case study of the propaganda usage on a real cause of double agent Sergei Skripal. The formal model describing statements published in web articles is announced and particular interesting aspects of used disinformation are provided together with the reasons, why the disinformation is published. The paper is aimed at the presentation of the data collection to have been created and provides a brief discussion on the used propaganda techniques. Keywords: Dezinformace; Web; Entropie; Pravděpodobnost Fulltext is available at external website.
Datová sada pro detekci dezinformačního obsahu – případová studie Novičok v Česku

Publikování dezinformací na webu hraje stále větší roli, proto vyvstává otázka, jak takovému obsahu čelit, a nebo na jeho potenciální závadnost alespoň upozornit. Propaganda využívá dezinformací k ...

Řimnáč, Martin
Ústav informatiky, 2018

Stav předaných dat a úprava rozdělení vybraných měření 2018
Novák, Jakub; Jiřina, M.; Benešová, Michaela
2018 - Czech
Zpráva se týká stavu předávaných dat a úpravy rozdělení vybraných měření pro rok 2018 v rámci projektu TDD-ČR. Cílem je informovat o aktuálním stavu dat a navrhnout opatření pro zachování reprezentativity celého vzorku. Jsou uvedena kritéria filtrace dat a navrženy postupy pro přerozdělení vybraných měření. Keywords: typový diagram dodávky; TDD; spotřeba plynu; měřicí místa; kritéria; filtrace; náhrady Available at various institutes of the ASCR
Stav předaných dat a úprava rozdělení vybraných měření 2018

Zpráva se týká stavu předávaných dat a úpravy rozdělení vybraných měření pro rok 2018 v rámci projektu TDD-ČR. Cílem je informovat o aktuálním stavu dat a navrhnout opatření pro zachování ...

Novák, Jakub; Jiřina, M.; Benešová, Michaela
Ústav informatiky, 2018

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