Browsing by Author "Gürel, Levent"
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Accelerating the multilevel fast multipole algorithm with the sparseapproximateinverse (SAI) preconditioning
Malas, T.; Gürel, Levent (Society for Industrial and Applied Mathematics, 2009)With the help of the multilevel fast multipole algorithm, integralequation methods can be used to solve reallife electromagnetics problems both accurately and efficiently. Increasing problem dimensions, on the other hand, ... 
Accuracy and efficiency considerations in the solution of extremely large electromagnetics problems
Gürel, Levent; Ergül, Özgür (IEEE, 2011)This study considers fast and accurate solutions of extremely large electromagnetics problems. Surface formulations of largescale objects lead to dense matrix equations involving millions of unknowns. Thanks to recent ... 
Accuracy considerations for the integralequation solutions of some canonical problems
Gürel, Levent (2012) 
Accuracy: The Frequently Overlooked Parameter in the Solution of Extremely Large Problems
Ergul, O.; Gürel, Levent (IEEE, 2011)We investigate error sources and their effects on the accuracy of solutions of extremely large electromagnetics problems with parallel implementations of the multilevel fast multipole algorithm (MLFMA). Accuracy parameters ... 
Accurate modeling of metamaterials with MLFMA
Ergül, Özgür; Ünal, Alper; Gürel, Levent (ESA Publications, 2006)Electromagnetic modelling of large metamaterial (MM) structures employing multilevel fast multipole algorithm (MLFMA) is reported. MMs are usually constructed by periodically embedding unit cells, such as splitring ... 
Accurate planewave excitation in the FDTD method
Gürel, Levent; Oğuz, Uğur; Arıkan, Orhan (IEEE, 1997)Different techniques are developed to implement planewave excitation on the finitedifference timedomain (FDTD) method, such as the initialcondition, the hardsource, and the connectingcondition techniques, for the ... 
Accurate solutions of extremely large integralequation problems in computational electromagnetics
Ergül, Ö; Gürel, Levent (IEEE, 201302)Accurate simulations of reallife electromagnetics problems with integral equations require the solution of dense matrix equations involving millions of unknowns. Solutions of these extremely large problems cannot be ... 
Accurate solutions of scattering problems involving lowcontrast dielectric objects with surface integral equations
Ergül, Özgür; Gürel, Levent (Institution of Engineering and Technology, 2007)We present the stabilization of the surface integral equations for accurate solutions of scattering problems involving lowcontrast dielectric objects. Unlike volume formulations, conventional surface formulations fail to ... 
Advanced numerical techniques for the scattering of waves by dielectric scatterers
Gürel, Levent (2012) 
Advanced partitioning and communication strategies for the efficient parallelization of the multilevel fast multipole algorithm
Ergül O.; Gürel, Levent (IEEE, 2010)Largescale electromagnetics problems can be solved efficiently with the multilevel fast multipole algorithm (MLFMA) [1], which reduces the complexity of matrixvector multiplications required by iterative solvers from O(N ... 
Algebraic acceleration and regularization of the source reconstruction method with the recompressed adaptive cross approximation
Kazempour, Mahdi; Gürel, Levent (IEEE, 2014)We present a compression algorithm to accelerate the solution of source reconstruction problems that are formulated with integral equations and defined on arbitrary threedimensional surfaces. This compression technique ... 
Analysis of composite objects involving multiple dielectric and metallic partswith the parallel multilevel fast multipole algorithm
Ergül, Özgür; Gürel, Levent (Applied Computational Electromagnetics Society, 201204) 
Analysis of dielectric photoniccrystal problems with MLFMA and Schurcomplement preconditioners
Ergül, Özgür; Malas, T.; Gürel, Levent (IEEE, 20110113)We present rigorous solutions of electromagnetics problems involving 3D dielectric photonic crystals (PhCs). Problems are formulated with recently developed surface integral equations and solved iteratively using the ... 
Analysis of doublenegative materials with surface integral equations and the multilevel fast multipole algorithm
Ergül O.; Gürel, Levent (IEEE, 2011)We present a fast and accurate analysis of doublenegative materials (DNMs) with surface integral equations and the multilevel fast multipole algorithm (MLFMA). DNMs are commonly used as simplified models of metamaterials ... 
Analysis of photoniccrystal problems with MLFMA and approximate Schur preconditioners
Ergül, Özgür; Malas, Tahir; Kılınç, Seçil; Sarıtaş, Serkan; Gürel, Levent (IEEE, 200907)We consider fast and accurate solutions of electromagnetics problems involving threedimensional photonic crystals (PhCs). Problems are formulated with the combined tangential formulation (CTF) and the electric and magnetic ... 
Application of signalprocessing techniques to dipole excitations in the finitedifference timedomain method
Oğuz, U.; Gürel, Levent (Taylor & Francis, 2002)The applications of discretetime signalprocessing techniques, such as windowing and filtering for the purpose of implementing accurate excitation schemes in the finitedifference timedomain (FDTD) method are demonstrated. ... 
Application of signalprocessing techniques to reduce the errors related to the FDTD excitations
Gürel, Levent; Oğuz, Uğur (IEEE, 2001)A study on the reduction of the errors related to the finitedifference timedomain (FDTD) excitations was performed by employing signalprocessing techniques. Planewave scattering problems were simulated. The improvements ... 
Approximate MLFMA as an efficient preconditioner
Malas, Tahir; Ergül, Özgür; Gürel, Levent (IEEE, 2007)In this work, we propose a preconditioner that approximates the dense system operator. For this purpose, we develop an approximate multilevel fast multipole algorithm (AMLFMA), which performs a much faster matrixvector ... 
Approximate Schur preconditioners for efficient solutions of dielectric problems formulated with surface integral equations
Malas, Tahir; Gürel, Levent (IEEE, 200907)We propose direct and iterative versions of approximate Schur preconditioners to increase robustness and efficiency of iterative solutions of dielectric problems formulated with surface integral equations. The performance ... 
Benchmark Solutions of Large Problems for Evaluating Accuracy and Efficiency of Electromagnetics Solvers
Ergul, O.; Gürel, Levent (IEEE, 2011)We present a set of benchmark problems involving conducting spheres and their solutions using a parallel implementation of the multilevel fast multipole algorithm (MLFMA). Accuracy of the implementation is tested by comparing ...