A multiprojection algorithm using Bregman projections in a product space

Generalized distances give rise to generalized projections into convex sets. An important question is whether or not one can use within the same projection algorithm different types of such generalized projections. This question has practical consequences in the area of signal detection and image recovery in situations that can be formulated mathematically as a convex feasibility problem. Using an extension of Pierra's product space formalism, we show here that a multiprojection algorithm converges. Our algorithm is fully simultaneous, i.e., it uses in each iterative stepall sets of the convex feasibility problem. Different multiprojection algorithms can be derived from our algorithmic scheme by a judicious choice of the Bregman functions which govern the process. As a by-product of our investigation we also obtain blockiterative schemes for certain kinds of linearly constraned optimization problems.     

On some methods for entropy maximization and matrix scaling

We describe and survey in this paper iterative algorithms for solving the discrete maximum entropy problem with linear equality constraints. This problem has applications e.g. in image reconstruction from projections, transportation planning, and matrix scaling. In particular we study local convergence and asymptotic rate of convergence as a function of the iteration parameter. For the trip distribution problem in transportation planning and the equivalent problem of scaling a positive matrix to achieve a priori given row and column sums, it is shown how the iteration parameters can be chosen in an optimal way. We also consider the related problem of finding a matrix X, diagonally similar to a given matrix, such that corresponding row and column norms in X are all equal. Reports of some numerical tests are given.     

The determinant of the scattering matrix and its relation to the number of eigenvalues

For a large class of scattering systems we study the behavior of the determinant of the scattering matrix as a function on the spectrum of the unperturbed operator. The variation of this determinant is related to the number of eigenvalues due to the perturbation. This relation generalizes results of Levinson and others. The range of physical systems to which these results apply is thus considerably extended.     

Algorithms for confluent Vandermonde systems

Two compact algorithms are developed for solving systems of linear equationsV x=b andV ^T a=f, whereV=V( ₀, ₁, ..., _n ) is a confluent Vandermonde matrix of Hermite type. The solution is obtained by one forward and one backward vector recursion, starting with the right hand side. The total amount of storage is only 2n. The number of arithmetic operations needed isO(n ²) and compares favourably with other proposed methods.     

Stability of suspensions, emulsions, and foams studied by a novel automated analyzer

The stability of dilute and concentrated dispersions (suspensions, emulsions, and foams) has been studied by a newly developed automated dispersion stability analyzer, DiStA 24. The analyzer operates by taking consecutive images of the samples studied and analyzing them by a personal computer (PC). As a result, the vertical profile of light scattered from each sample is obtained, recorded, and analyzed at time intervals preset by the computer software. In this way, the destructive processes in dispersions (sedimentation, creaming, and coalescence) can be detected well before it is possible by the naked eye and monitored automatically in the temperature range 0-50 degrees C. The new analyzer differs from the existing instruments by its simplicity and high productivity, allowing 24 samples to be measured simultaneously.     

New upper limit on the total neutrino mass from the 2 degree field galaxy redshift survey

We constrain f(nu) identical with Omega(nu)/Omega(m), the fractional contribution of neutrinos to the total mass density in the Universe, by comparing the power spectrum of fluctuations derived from the 2 Degree Field Galaxy Redshift Survey with power spectra for models with four components: baryons, cold dark matter, massive neutrinos, and a cosmological constant. Adding constraints from independent cosmological probes we find f(nu)<0.13 (at 95% confidence) for a prior of 0.1相似文献