Browsing by Subject "Approximation methods"
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Item Open Access KiMPA: A kinematics-based method for polygon approximation(Springer, Berlin, Heidelberg, 2002) Şaykol, Ediz; Gülesir, Gürcan; Güdükbay, Uğur; Ulusoy, ÖzgürIn different types of information systems, such as multimedia information systems and geographic information systems, object-based information is represented via polygons corresponding to the boundaries of object regions. In many applications, the polygons have large number of vertices and edges, thus a way of representing the polygons with less number of vertices and edges is developed. This approach, called polygon approximation, or polygon simplification, is basically motivated with the difficulties faced in processing polygons with large number of vertices. Besides, large memory usage and disk requirements, and the possibility of having relatively more noise can also be considered as the reasons for polygon simplification. In this paper, a kinematics-based method for polygon approximation is proposed. The vertices of polygons are simplified according to the velocities and accelerations of the vertices with respect to the centroid of the polygon. Another property of the proposed method is that the user may set the number of vertices to be in the approximated polygon, and may hierarchically simplify the output. The approximation method is demonstrated through the experiments based on a set of polygonal objects. © Springer-Verlag Berlin Heidelberg 2002.Item Open Access Polar code construction for non-binary source alphabets(IEEE, 2012) Çaycı, Semih; Arıkan, Orhan; Arıkan, ErdalIn this paper, approximation methods for binary polar code construction proposed by Tal and Vardy are extended to non-binary source alphabets. Additionally, a new approximation method that enables accurate polar code construction with less usage of computational resources is proposed. Efficiency and accuracy of proposed methods are supported analytically and numerically. © 2012 IEEE.Item Open Access Preconditioning large integral-equation problems involving complex targets(IEEE, 2008-07) Malas, Tahir; Gürel, LeventWhen the target problem is small in terms of the wavelength, simple preconditioners, such as BDP, may sufficiently accelerate the convergence. On the other hand, for large-scale problems, the matrix equations become much more difficult to solve, and therefore, the importance of preconditioning become more evident for both formulations. In this paper, we demonstrate the use of novel, strong, and efficient preconditioners for the solutions of large EFIE and CFIE problems.Item Open Access Stride-to-stride energy regulation for robust self-stability of a torque-actuated dissipative spring-mass hopper(A I P Publishing LLC, 2010) Ankarali, M. M.; Saranli, U.In this paper, we analyze the self-stability properties of planar running with a dissipative spring-mass model driven by torque actuation at the hip. We first show that a two-dimensional, approximate analytic return map for uncontrolled locomotion with this system under a fixed touchdown leg angle policy and an open-loop ramp torque profile exhibits only marginal self-stability that does not always persist for the exact system. We then propose a per-stride feedback strategy for the hip torque that explicitly compensates for damping losses, reducing the return map to a single dimension and substantially improving the robust stability of fixed points. Subsequent presentation of simulation evidence establishes that the predictions of this approximate model are consistent with the behavior of the exact plant model. We illustrate the relevance and utility of our model both through the qualitative correspondence of its predictions to biological data as well as its use in the design of a task-level running controller. © 2010 American Institute of Physics.