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Number of found documents:
1598
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Two limited-memory optimization methods with minimum violation of the previous quasi-Newton equations
Vlček, Jan; Lukšan, Ladislav
2020 - English
Limited-memory variable metric methods based on the well-known BFGS update are widely used for large scale optimization. The block version of the BFGS update, derived by Schnabel (1983), Hu and Storey (1991) and Vlček and Lukšan (2019), satisfies the quasi-Newton equations with all used difference vectors and for quadratic objective functions gives the best improvement of convergence in some sense, but the corresponding direction vectors are not descent directions generally. To guarantee the descent property of direction vectors and simultaneously violate the quasi-Newton equations as little as possible in some sense, two methods based on the block BFGS update are proposed. They can be advantageously combined with methods based on vector corrections for conjugacy (Vlček and Lukšan, 2015). Global convergence of the proposed algorithm is established for convex and sufficiently smooth functions. Numerical experiments demonstrate the efficiency of the new methods.
Keywords:
unconstrained minimization; variable metric methods; limited-memory methods; variationally derived methods; global convergence; numerical results
Available in a digital repository NRGL
Two limited-memory optimization methods with minimum violation of the previous quasi-Newton equations
Limited-memory variable metric methods based on the well-known BFGS update are widely used for large scale optimization. The block version of the BFGS update, derived by Schnabel (1983), Hu and Storey ...
Linear-time Algorithms for Largest Inscribed Quadrilateral
Keikha, Vahideh
2020 - English
Let P be a convex polygon of n vertices. We present a linear-time algorithm for the problem of computing the largest-area inscribed quadrilateral of P. We also design the parallel version of the algorithm with O(log n) time and O(n) work in CREW PRAM model, which is quite work optimal. Our parallel algorithm also computes all the antipodal pairs of a convex polygon with O(log n) time and O(log2n+s) work, where s is the number of antipodal pairs, that we hope is of independent interest. We also discuss several approximation algorithms (both constant factor and approximation scheme) for computing the largest-inscribed k-gons for constant values of k, in both area and perimeter measures.
Keywords:
Maximum-area quadrilateral; extreme area k-gon
Available in a digital repository NRGL
Linear-time Algorithms for Largest Inscribed Quadrilateral
Let P be a convex polygon of n vertices. We present a linear-time algorithm for the problem of computing the largest-area inscribed quadrilateral of P. We also design the parallel version of the ...
Potential Radioactive Hot Spots Induced by Radiation Accident Being Underway of Atypical Low Wind Meteorological Episodes
Pecha, Petr; Tichý, Ondřej; Pechová, E.
2020 - English
Hypothetical radioactivity release with potentially high variability of the source strength is examined. The interactions of the radioactive cloud with surface and atmospheric precipitation are studied and possible adverse consequences on the environment are estimated. The worst-case scenario is devised in two stages starting with a calm meteorological situation succeeded by wind. At the first stage, the discharges of radionuclides into the motionless ambient atmosphere are assumed. During several hours of this calm meteorological situation, a relatively significant level of radioactivity can be accumulated around the source. At the second stage, the calm is assumed to terminate and convective movement of the air immediately starts. The pack of accumulated radioactivity in the form of multiple Gaussian puffs is drifted by wind and pollution is disseminated over the terrain. The results demonstrate the significant transport of radioactivity even behind the protective zone of a nuclear facility (up to between 15 and 20 km). In the case of rain, the aerosols are heavily washed out and dangerous hot spots of the deposited radioactivity can surprisingly emerge even far from the original source of the pollution.
Keywords:
radioactivity; atmospheric dissemination; deposition hot-spots
Fulltext is available at external website.
Potential Radioactive Hot Spots Induced by Radiation Accident Being Underway of Atypical Low Wind Meteorological Episodes
Hypothetical radioactivity release with potentially high variability of the source strength is examined. The interactions of the radioactive cloud with surface and atmospheric precipitation are ...
DEnFi: Deep Ensemble Filter for Active Learning
Ulrych, Lukáš; Šmídl, Václav
2020 - English
Deep Ensembles proved to be a one of the most accurate representation of uncertainty for deep neural networks. Their accuracy is beneficial in the task of active learning where unknown samples are selected for labeling based on the uncertainty of their prediction. Underestimation of the predictive uncertainty leads to poor exploration of the method. The main issue of deep ensembles is their computational cost since multiple complex networks have to be computed in parallel. In this paper, we propose to address this issue by taking advantage of the recursive nature of active learning. Specifically, we propose several methods how to generate initial values of an ensemble based of the previous ensemble. We provide comparison of the proposed strategies with existing methods on benchmark problems from Bayesian optimization and active classification. Practical benefits of the approach is demonstrated on example of learning ID of an IoT device from structured data using deep-set based networks.
Keywords:
Deep Ensembles; uncertainty; neural networks
Fulltext is available at external website.
DEnFi: Deep Ensemble Filter for Active Learning
Deep Ensembles proved to be a one of the most accurate representation of uncertainty for deep neural networks. Their accuracy is beneficial in the task of active learning where unknown samples are ...
Macroeconomic Responses of Emerging Market Economies to Oil Price Shocks: Analysis by Region and Resource Profile
Togonidze, S.; Kočenda, Evžen
2020 - English
This study employs a vector autoregressive (VAR) model to analyse how oil price shocks affect macroeconomic fundamentals in emerging economies. Findings from existing literature remain inconclusive how macroeconomic variables fare towards shocks, especially in emerging economies. The objective of our study is to uncover if analysis by region (Latin America and the Caribbean, East Asia and the Pacific, Europe, and Central Asia) and resource intensity of economies (oil exporters, oil importers, minerals exporters, and less resource intensive). Our unique approach forms part of our contribution to the literature. We find that Latin America and the Caribbean are least affected by oil price shocks, while in East Asia and the Pacific the response of inflation and interest rate to oil price shocks is positive, and output growth is negative. Our analysis by resource endowment fails to show oil price shocks’ ability to explain huge variations in macroeconomic variables in oil importing economies. Further sensitivity analysis using US interest rates as an alternative source of external shocks to emerging economies establishes a significant response of interest rate responses to US interest rate in Europe and Central Asia, and in inflation in Latin America and the Caribbean. We also find that regardless of resource endowment, the response of output growth and capital to a positive US interest rate shock is negative and significant in EMs. Our results are persuasive that resource intensity and regional factors impact the responsiveness of emerging economies to oil price shocks, thus laying a basis for policy debate.\n
Keywords:
Emerging market economies; Oil price shocks; Output growth; Panel VAR
Fulltext is available at external website.
Macroeconomic Responses of Emerging Market Economies to Oil Price Shocks: Analysis by Region and Resource Profile
This study employs a vector autoregressive (VAR) model to analyse how oil price shocks affect macroeconomic fundamentals in emerging economies. Findings from existing literature remain inconclusive ...
Measurements on TR-U-9 Cascade
Luxa, Martin; Šimurda, David; Hála, Jindřich
2020 - English
The report contains results and evaluation of conducted optical (interferometry and schlieren technique), pneumatic and CTA (hot films) measurements on the second variant of the tip section, intended for long rotor blade.
Keywords:
transonic flow; experimental aerodynamic; steam turbine
Available at various institutes of the ASCR
Measurements on TR-U-9 Cascade
The report contains results and evaluation of conducted optical (interferometry and schlieren technique), pneumatic and CTA (hot films) measurements on the second variant of the tip section, intended ...
The Equation |x| - |Ax| = b
Rohn, Jiří
2020 - English
We formulate conditions on A and b under which the double absolute value equation |x| - |Ax| = b possesses in each orthant a unique solution which, moreover, belongs to the interior of that orthant.
Keywords:
absolute value equation; double absolute value equation; orthantwise solvability; theorem of the alternatives
Available in a digital repository NRGL
The Equation |x| - |Ax| = b
We formulate conditions on A and b under which the double absolute value equation |x| - |Ax| = b possesses in each orthant a unique solution which, moreover, belongs to the interior of that orthant.
Measurements on KR-D-2 Blade Cascade
Šimurda, David; Luxa, Martin; Radnic, Tomáš; Hála, Jindřich
2019 - English
This report contains results and evaluation of aerodynamic measurements conducted on second variant of transonic compressor blade cascade.
Keywords:
transonic compressor blade; aerodynamic measurements; axial compressor
Available at various institutes of the ASCR
Measurements on KR-D-2 Blade Cascade
This report contains results and evaluation of aerodynamic measurements conducted on second variant of transonic compressor blade cascade.
Distribution of the external wind pressure coefficients on the surface of the façade of the high‐rise building "KINEUM" determined from the wind tunnel measurements
Hračov, Stanislav; Macháček, Michael
2019 - English
The report describes the procedure and results of the measurements of aerodynamic model of the planned high-rise building in Gothenburg in Sweden. The determined wind pressure distribution on individual surfaces of the building for several wind directions are presented in the form of external pressure coefficients. The obtained pressure coefficients are subsequently used by the client for the design of façade elements loaded by the wind.
Keywords:
external pressure coefficient; wind load; high-rise building
Available at various institutes of the ASCR
Distribution of the external wind pressure coefficients on the surface of the façade of the high‐rise building "KINEUM" determined from the wind tunnel measurements
The report describes the procedure and results of the measurements of aerodynamic model of the planned high-rise building in Gothenburg in Sweden. The determined wind pressure distribution on ...
On Yield Surface Detection, Experiments by Finite Element Method
Klepač, Vilém; Liu, Li-Wei
2019 - English
In the submitted report it is described, how experiments by FEM are designed for\nmore precise detection of yield point. Content of report can be devided to these\nareas:\n- Intership travel report\n- Idea of research topic\n- Develop software tools
Keywords:
FEM; yield surface; plasticity
Available at various institutes of the ASCR
On Yield Surface Detection, Experiments by Finite Element Method
In the submitted report it is described, how experiments by FEM are designed for\nmore precise detection of yield point. Content of report can be devided to these\nareas:\n- Intership travel ...
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