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IEEE International Symposium on Biomedical Imaging

作者： Jun Ma Department of Statistics Macquarie University NSW Australia

ISBN: (纸本)9781424420025

This paper introduces a multiplicative iterative (MI) algorithm for image reconstructions in tomography. This algorithm can accommodate objective functions deduced from different probability models for measurements. Poisson and Gaussian (for both emission and transmission scans), or shifted Poisson (for precorrected PET and X-ray CT), are examples of such measurement probability models. This MI algorithm is very easy to implement and respects the positivity constraint. Furthermore, an exact or approximate line search step can be easily incorporated into this algorithm so that the objective functions are guaranteed to increase during the iterations.

关键词： iterative algorithms Image reconstruction Probability Positron emission tomography Computed tomography Independent component analysis Statistics X-ray imaging Least squares approximation Entropy

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A rotating and squashing projector-backprojector pair for fan-beam and cone-beam iterative algorithms

A rotating and squashing projector-backprojector pair for fa...

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IEEE Symposium on Nuclear Science (NSS/MIC)

作者： G.L. Zeng Y.-L. Hsieh G.T. Gullberg Department of Radiology University of Utah Salt Lake UT USA

The authors propose and implement a rotating-and-squashing projector-backprojector pair for fan-beam and cone-beam iterative algorithms. The motivation of their investigation is to significantly reduce both computation time and reconstruction artifacts when implementing attenuation, geometric and scatter correction models. At each projection angle, the authors' projector/backprojector first rotates the image volume so that the front face of the volume is parallel to the detector, then squashes the image volume so that the fan-beam and cone-beam rays are converted into parallel rays. In the authors' implementation, these two steps are combined and they only interpolate the voxel values once. The projection operation is achieved by a simple summation, and the backprojection operation is achieved by copying the projection array to the image volume. Another advantage of this projector/backprojector is that the system point response function can be deconvolved via the fast Fourier transform using the shift-invariant property of the point response function when the voxel-to-detector distance is constant. At each projection angle, the authors rotate and squash the image volume using interpolations. This causes smoothing of the image. However, this smoothing can be modeled as a point spread function and be deconvolved. The fan-beam and cone-beam rotating-and-squashing projector/backprojector have been implemented on a SPECT system for the EM-ML algorithm.< >

关键词： Face detection Smoothing methods iterative algorithms Image reconstruction Attenuation Scattering Solid modeling Detectors Image converters Fast Fourier transforms

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CRAC: a Grid Environment to Solve Scientific Applications with Asynchronous iterative algorithms

CRAC: a Grid Environment to Solve Scientific Applications wi...

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International Symposium on Parallel and Distributed Processing (IPDPS)

作者： Raphael Couturier Stephane Domas IUT de Belfort-Montbéliard Laboratoire d'Informatique de l'Université de Franche-Comté (LIFC) Belfort France

This paper presents CRAC, an environment dedicated to design efficient asynchronous iterative algorithms for a grid architecture. Those algorithms are particularly suited for grid architecture since they naturally allow to overlap communications by computations. Each processor computes its iterations freely without any synchronization with its neighbors. All the characteristics of CRAC are described. A real application using four distant clusters, with a total of 120 processors, shows the interest of this environment and of asynchronous algorithms.

关键词： iterative algorithms Java Computer architecture Clustering algorithms Grid computing Message passing Context Algorithm design and analysis Application software Parallel machines

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Interference Cancelation in Non-Coherent CDMA Systems Using Parallel iterative algorithms

Interference Cancelation in Non-Coherent CDMA Systems Using ...

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IEEE Conference on Wireless Communications and Networking

作者： Kamal Shahtalebi Gholam Reza Bakhshi Hamidreza Saligheh Rad Department of Information Technology University of Isfahan Isfahan Iran Department of Electrical Engineering Yazd University Yazd Iran School of Engineering and Applied Sciences Harvard University Cambridge MA USA

Parallel least mean square-partial parallel interference cancellation (PLMS-PPIC) is a partial interference cancellation which employs adaptive multistage structure (Shahtalebi et al., 2007). In this algorithm the channel phases for all users are assumed to be known. Having only their quarters in (0, 2pi), a modified version of PLMS-PPIC is proposed in this paper to simultaneously estimate the channel phases and the cancellation weights. Simulation examples are given in the cases of balanced, unbalanced and time varying channels to show the performance of the modified PLMS-PPIC method.

关键词： Interference cancellation Multiaccess communication iterative algorithms Phase estimation Multiple access interference Detectors Peer to peer computing Communications Society Information technology USA Councils

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Safety Verification of iterative algorithms over Polynomial Vector Fields

Safety Verification of Iterative Algorithms over Polynomial ...

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IEEE Conference on Decision and Control

作者： Mardavij Roozbehani Alexandre Megretski Eric Feron Department of Aeronautics and Astronautics Massachusetts Institute of Technology Cambridge MA USA Electrical engineering MIT USA AeroSpace engineering Georgia Institute of Technology Atlanta GA USA

ISBN: (纸本)1424401704;9781424401703

iterative algorithms such as the Newton method or the steepest gradient method appear in real-time software to solve online optimization problems as part of autonomous decision making algorithms. Proving safety and in particular convergence properties of such methods in their generic form is hopeless. However, for a special class of problems over a limited range of inputs and uncertain parameters, such task may become possible. In this paper, we consider applications of the Newton method to polynomial root finding and suggest new methods, based on Lyapunov invariance analysis and sum of squares programming to prove convergence and other performance properties of such algorithms. Generic forms for such Lyapunov invariants are presented and it is shown how the search for the certificates of performance can be formulated as a sum of squares program. The proof methods can be automated and thus integrated within a verification and validation workspace for software verification

关键词： Safety iterative algorithms Polynomials Newton method Convergence Gradient methods Optimization methods Decision making Software algorithms Performance analysis

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Near-optimal data detection for two-dimensional ISI/AWGN channels using concatenated modeling and iterative algorithms

Near-optimal data detection for two-dimensional ISI/AWGN cha...

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IEEE International Conference on Communications (ICC)

作者： Xiaopeng Chen K.M. Chugg Communication Sciences Institute Electrical Engineering-Systems Department University of Southern California Los Angeles CA USA

The general problem of performing digital data detection for a two-dimensional (2D) systems is considered with the specific application of page-access optical memory systems in mind. A simple 2D intersymbol interference (ISI) channel with additive white Gaussian noise (AWGN) is assumed. An equivalent signal model consisting of two one-dimensional systems separated by a block interleaver is developed and used to motivate the application of previously developed algorithms for data detection in concatenated systems. The resulting iterative detection algorithms, which are based on soft-output algorithms, are demonstrated to achieve near-optimal performance even for very severe 2D ISI channels.

关键词： Intersymbol interference AWGN channels Concatenated codes Optical noise Additive white noise Gaussian noise iterative algorithms Detection algorithms Error probability Data storage systems

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PAVE: parallel algorithms visually explored, a prototype tool for the investigation of data structures in parallel numerical iterative algorithms

PAVE: parallel algorithms visually explored, a prototype too...

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Euromicro Workshop on Parallel and Distributed Processing

作者： E.J. Stuart J.S. Weston Department of Computing Science University of Ulster Coleraine UK

It is commonly acknowledged that since the advent of supercomputing, the ability of computer scientists to efficiently interpret the large masses of data produced has been significantly reduced. By transforming the masses of numbers produced into intuitive and instructive pictures visualization offers the scientist a way of seeing the unseen. In this paper a prototype algorithm investigation tool is introduced and two specific representations of the tool are discussed in detail. Subsequently, an iterative algorithm is investigated using the tool and data extracted from the algorithm is analysed using visual representations. The hypothesis proposed as a direct consequence of the visualization of the data is implemented on an array processor and experimental results are presented for a variety of test cases.< >

关键词： Parallel algorithms Prototypes Data visualization iterative algorithms Data structures Algorithm design and analysis Parallel processing Biological system modeling Performance analysis Concurrent computing

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iterative AND SEQUENTIAL algorithms FOR MULTISENSOR SIGNAL ENHANCEMENT

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IEEE TRANSACTIONS ON SIGNAL PROCESSING 1994年第4期42卷 846-859页

作者： WEINSTEIN, E OPPENHEIM, AV FEDER, M BUCK, JR WOODS HOLE OCEANOG INST DEPT APPL OCEAN PHYS & ENGNWOODS HOLEMA 02543 MIT DEPT ELECT ENGN & COMP SCICAMBRIDGEMA 02139 MIT ELECTR RES LABCAMBRIDGEMA 02139 MIT WHOIJOINT PROGRAM APPL OCEAN SCI & ENGNCAMBRIDGEMA 02139

In problems of enhancing a desired signal in the presence of noise, multiple sensor measurements will typically have components from both the signal and the noise sources. When the systems that couple the signal and the noise to the sensors are unknown, the problem becomes one of joint signal estimation and system identification. In this paper, we specifically consider the two-sensor signal enhancement problem in which the desired signal is modeled as a Gaussian autoregressive (AR) process, the noise is modeled as a white Gaussian process, and the coupling systems are modeled as linear time-invariant finite impulse response (FIR) filters. Our primary approach consists of modeling the observed signals as outputs of a stochastic dynamic linear system, and we apply the Estimate-Maximize (EM) algorithm for jointly estimating the desired signal, the coupling systems, and the unknown signal and noise spectral parameters. The resulting algorithm can be viewed as the time-domain version of our previously suggested frequency-domain approach [4], where instead of the noncausal frequency-domain Wiener filter, we use the Kalman smoother. This time-domain approach leads naturally to a sequential/adaptive algorithm by replacing the Kalman smoother with the Kalman filter, and in place of successive iterations on each data block, the algorithm proceeds sequentially through the data with exponential weighting applied to allow adaption to nonstationary changes in the structure of the data. A computationally efficient implementation of the algorithm is developed by exploiting the structure of the Kalman filtering equations. An expression for the log-likelihood gradient based on the Kalman smoother/filter output is also developed and used to incorporate efficient gradient-based algorithms in the estimation process.

关键词： iterative algorithms Signal processing Finite impulse response filter Kalman filters Noise measurement Sensor systems Estimation System identification Gaussian noise Gaussian processes

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Mapping iterative algorithms onto processor arrays by the use of Petri Net models

Mapping iterative algorithms onto processor arrays by the us...

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International Conference on Massively Parallel Computing Systems

作者： K.E. Karagianni E.D. Kyriakis-Bitzaros T. Stouraitis Department of Electrical Engineering University of Patras Patras Greece

In this paper, Petri Nets (PNs) are used for deriving efficient mapping transformations of a wide class of algorithms to processor arrays. In the proposed methodology, given an algorithm and the interconnections of the processor array, two PNs are constructed: one that is related to the algorithm and one that is related to the processor array. The former PN models the execution of the algorithm and differs drastically from the common data-flow methods. Based on properties of PNs and on the reachability tree analysis technique, a theorem is given, through which the two PN model suggest all possible ways of implementing the algorithm by the processor array.< >

关键词： iterative algorithms Power system modeling Algorithm design and analysis Concurrent computing Timing Tree graphs Computer aided manufacturing Petri nets Parallel architectures Optimization methods

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Optimal iterative algorithms in Gabor analysis

Optimal iterative algorithms in Gabor analysis

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IEEE-SP International Symposium on Time-Frequency and Time-Scale Analysis

作者： H.G. Feichtinger Department of Mathematics NUHAG-Numerical Harmonic Analysis Group University of Vienna Vienna Austria

Gabor expansions of discrete signals and images have a wide range of applications in signal analysis and pattern recognition. It is well known that the difficulty in expanding a 1-D or a 2-D signal into a Gabor series is the non-orthogonality of the building blocks, which are time-frequency shifted versions (along some lattice in the TF-plane) of a, given Gabor atom. The theory of frames (Gabor or Weyl-Heisenberg frames) has reached fame as the appropriate tool for resolving the problem. In particular, the dual frame turns out to be again a Gabor frame with respect to the same lattice, and its generating function is called the dual Gabor atom g/spl tilde/. It is obtained by applying the inverse of the frame operator S to the original frame (or just the Gabor atom), i.e. g/spl tilde/= S/sup -1/g. There is also another important use for the dual Gabor window. Given the sampled STFT (short time or sliding window Fourier transform) of some signal x with respect to the window g over the same lattice it is possible to recover the signal x using a simple Shannon-type reconstruction formula. We present some basic ideas behind a new family of iterative algorithms for determining the dual Gabor atom in the finite (discrete and periodic) case. They are mainly based on the conjugate gradient methods in combination with structural properties of the Gabor frame operator.< >

关键词： iterative algorithms Algorithm design and analysis Lattices Signal analysis Pattern recognition Time frequency analysis Signal resolution Fourier transforms Image reconstruction Gradient methods

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