A generalized cyclic iterative method for solving variational inequalities over the solution set of a split common fixed point problem

For solving the large-scale linear least-squares problem, we propose a block version of the randomized extended Kaczmarz method, called the two-subspace randomized extended Kaczmarz method, which does not require any row or column paving. Theoretical analysis and numerical results show that the two-subspace randomized extended Kaczmarz method is much more efficient than the randomized extended Kaczmarz method. When the coefficient matrix is of full column rank, the two-subspace randomized extended Kaczmarz method can also outperform the randomized coordinate descent method. If the linear system is consistent, we remove one of the iteration sequences in the two-subspace randomized extended Kaczmarz method, which approximates the projection of the right-hand side vector onto the orthogonal complement space of the range space of the coefficient matrix, and obtain the generalized two-subspace randomized Kaczmarz method, which is actually a generalization of the two-subspace randomized Kaczmarz method without the assumptions of unit row norms and full column rank on the coefficient matrix. We give the upper bound for the convergence rate of the generalized two-subspace randomized Kaczmarz method which also leads to a better upper bound for the convergence rate of the two-subspace randomized Kaczmarz method.

     

Diode laser spectrum of the ν6 band of CH3I using a novel étalon as a calibration scale

The ΔK = Δl = +1 transitions of the ν₆ band of the CH₃I molecule were measured by a tunable diode laser spectrometer. A newly designed Fabry-Perot étalon with a free spectral range of 0.00945 cm^?1 was used to calibrate the line position very precisely. The present data were analyzed together with the previously reported transition wavenumbers, and precise molecular constants have been obtained.     

Conservation Properties of Smoothed Particle Hydrodynamics Applied to the Shallow Water Equation

Kelvin's circulation theorem and its implications for potential vorticity (PV) conservation are among the most fundamental concepts in ideal fluid dynamics. In this note, we discuss the numerical treatment of these concepts with the Smoothed Particle Hydrodynamics (SPH) and related methods. We show that SPH satisfies an exact circulation theorem in an interpolated velocity field, and that, when appropriately interpreted, this leads to statements of conservation of PV and generalized enstrophies. We also indicate some limitations where the analogy with ideal fluid dynamics breaks down.     

Finding the projection of a point onto the intersection of convex sets via projections onto half-spaces

We present a modification of Dykstra's algorithm which allows us to avoid projections onto general convex sets. Instead, we calculate projections onto either a half-space or onto the intersection of two half-spaces. Convergence of the algorithm is established and special choices of the half-spaces are proposed.The option to project onto half-spaces instead of general convex sets makes the algorithm more practical. The fact that the half-spaces are quite general enables us to apply the algorithm in a variety of cases and to generalize a number of known projection algorithms.The problem of projecting a point onto the intersection of closed convex sets receives considerable attention in many areas of mathematics and physics as well as in other fields of science and engineering such as image reconstruction from projections.In this work we propose a new class of algorithms which allow projection onto certain super half-spaces, i.e., half-spaces which contain the convex sets. Each one of the algorithms that we present gives the user freedom to choose the specific super half-space from a family of such half-spaces. Since projecting a point onto a half-space is an easy task to perform, the new algorithms may be more useful in practical situations in which the construction of the super half-spaces themselves is not too difficult.