Browsing by Subject "Parallel Algorithms"
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Item Open Access Efficient fast hartley transform algorithms for hypercube-connected multicomputers(IEEE, 1995) Aykanat, Cevdet; Derviş, A.Although fast Hartley transform (FHT) provides efficient spectral analysis of real discrete signals, the literature that addresses the parallelization of FHT is extremely rare. FHT is a real transformation and does not necessitate any complex arithmetics. On the other hand, FHT algorithm has an irregular computational structure which makes efficient parallelization harder. In this paper, we propose a efficient restructuring for the sequential FHT algorithm which brings regularity and symmetry to the computational structure of the FHT. Then, we propose an efficient parallel FHT algorithm for medium-to-coarse grain hypercube multicomputers by introducing a dynamic mapping scheme for the restructured FHT. The proposed parallel algorithm achieves perfect load-balance, minimizes both the number and volume of concurrent communications, allows only nearest-neighbor communications and achieves in-place computation and communication. The proposed algorithm is implemented on a 32-node iPSC/21 hypercube multicomputer. High-efficiency values are obtained even for small size FHT problems. © 1995 IEEEItem Open Access A parallel progressive radiosity algorithm based on patch data circulation(Pergamon Press, 1996) Aykanat, Cevdet; Çapin, T. K.; Özgüç, B.Abstract - Current research on radiosity has concentrated on increasing the accuracy and the speed of the solution. Although algorithmic and meshing techniques decrease the execution time, still excessive computational power is required for complex scenes. Hence, parallelism can be exploited for speeding up the method further. This paper aims at providing a thorough examination of parallelism in the basic progressive refinement radiosity, and investigates its parallelization on distributed-memory parallel architectures. A synchronous scheme, based on static task assignment, is proposed to achieve better coherence for shooting patch selections. An efficient global circulation scheme is proposed for the parallel light distribution computations, which reduces the total volume of concurrent communication by an asymptotical factor. The proposed parallel algorithm is implemented on an Intel's iPSC/2 hypercube multicomputer. Load balance qualities of the proposed static assignment schemes are evaluated experimentally. The effect of coherence in the parallel light distribution computations on the shooting patch selection sequence is also investigated. Theoretical and experimental evaluation is also presented to verify that the proposed parallelization scheme yields equally good performance on multicomputers implementing the simplest (e.g. ring) as well as the richest (e.g. hypercube) interconnection topologies. This paper also proposes and presents a parallel load re-balancing scheme which enhances our basic parallel radiosity algorithm to be usable in the parallelization of radiosity methods adopting adaptive subdivision and meshing techniques. Copyright © 1996 Elsevier Science Ltd.Item Open Access A parallel scaled conjugate-gradient algorithm for the solution phase of gathering radiosity on hypercubes(Springer, 1997) Kurç, T. M.; Aykanat, Cevdet; Özgüç, B.Gathering radiosity is a popular method for investigating lighting effects in a closed environment. In lighting simulations, with fixed locations of objects and light sources, the intensity and color and/or reflectivity vary. After the form-factor values are computed, the linear system of equations is solved repeatedly to visualize these changes. The scaled conjugate-gradient method is a powerful technique for solving large sparse linear systems of equations with symmetric positive definite matrices. We investigate this method for the solution phase. The nonsymmetric form-factor matrix is transformed into a symmetric matrix. We propose an efficient data redistribution scheme to achieve almost perfect load balance. We also present several parallel algorithms for form-factor computation.