The mol-ecular structure of the title compound, C4H12N2O4S2, has crystallographic inversion symmetry. The central N-C-C-N moiety was refined as disordered over two sets of sites with an approximate occupancy ratio of 3:1 [0.742 (15):0.258 (15). In the crystal, N-H⋯O hydrogen bonds link adjacent mol-ecules into a thick sheet structure parallel to the b-axis direction.

We have recently developed a preconditioning scheme that can be viewed as a hybrid of incomplete factorization and sparse approximate inversion methods. This hybrid scheme attempts to deliver the strengths of both types of preconditioning schemes to accelerate the convergence of Conjugate Gradients (CG) on multiprocessors. We provide an overview of our algorithm and report on initial results fo...

We present some experiences with the problem of multiple genome comparison , analogous to multiple sequence alignment in sequence comparison, under the inversion and transposition distance metrics, given a xed phylogeny. We rst describe a heuristic for the case in which phylogeny is a star on three vertices and then use this to approximate the multiple genome comparison problem via local search.

In the title compound, C22H16Br2O2, which has approximate non-crystallographic inversion symmetry, the dihedral angles between the central ring and the pendant rings are 89.1 (4) and 82.4 (3)°; the dihedral angle between the pendant rings is 12.1 (4)°. In the crystal, the packing is influenced by van der Waals forces and no aromatic π-π stacking is observed.

A fast approximate inversion algorithm is proposed for two-level Toeplitz matrices (block Toeplitz matrices with Toeplitz blocks). It applies to matrices that can be sufficiently accurately approximated by matrices of low Kronecker rank and involves a new class of tensor-displacement-rank structured (TDS) matrices. The complexity depends on the prescribed accuracy and typically is o(n) for matr...

Characterizing the set of all parameter vectors such that their image by a vector function belongs to a given set is a set-inversion problem. The algorithm SIVIA (Set Inversion Via Interval Analysis) makes it possible to perform this task in an approximate but guaranteed way. In the examples treated so far, the function to be inverted was given either explicitly or by a sequential algorithm. In...

We discuss methods to compute error bounds for extremely ill-conditioned problems. As a model problem we treat matrix inversion. We demonstrate that additive corrections to improve an approximate inverse are useful for ill-conditioned problems, but hardly usable for extremely ill-conditioned problems. Here multiplicative corrections can be used, including the possibility to compute guaranteed e...

This version is made available in accordance with publisher policies. Please cite only the published version using the reference above. Abstract: In a variety of fields, system inversion is often required in order to determine inputs from measured or for desired outputs. However, inverse systems are often non-proper in the sense that they require differentiators in their realisation. This leads...

This paper introduces a perturbative inversion algorithm for determining sea floor acoustic properties, which uses modal amplitudes as input data. Perturbative inverse methods have been used in the past to estimate bottom acoustic properties in sediments, but up to this point these methods have used only the modal eigenvalues as input data. As with previous perturbative inversion methods, the o...

This paper provides a detailed theoretical analysis of methods to approximate the solutions of high-dimensional (> 10) linear Bayesian problems. An optimal low-rank projection that maximizes the information content of the Bayesian inversion is proposed and efficiently constructed using a scalable randomized SVD algorithm. Useful optimality results are established for the associated posterior er...