Towards a stable static pivoting strategy for the sequential and parallel solution of sparse symmetric indefinite systems

Towards a stable static pivoting strategy for the sequential and parallel solution of sparse symmetric indefinite system

Strategies for scaling and pivoting for sparse symmetric indefinite problems

indefinite problem

Unsymmetric ordering using a constrained Markowitz scheme

We present a family of ordering algorithms that can be used as a preprocessing step prior to performing sparse LU factorization. The ordering algorithms simultaneously achieve the objectives of selecting numerically good pivots and preserving the sparsity. We describe the algorithmic properties and challenges in their implementation. By mixing the two objectives we show that we can reduce the amount of fill-in in the factors and reduce the number of numerical problems during factorization. On a set of large unsymmetric real problems, we obtained the median reductions of 12% in the factorization time, of 13% in the size of the LU factors, of 20% in the number of operations performed during the factorization phase, and of 11% in the memory needed by the multifrontal solver MA41-UNS. A byproduct of this ordering strategy is an incomplete LU-factored matrix that can be used as a preconditioner in an iterative solver

Planning Acquisitions for an Ocean Global Surveillance Mission.

In this paper, we present the problem of planning the acquisitions performed by a constellation of radar satellites in order to fulfil as well as possible an ocean global surveillance mission. Then, we describe the local search algorithm, inspired by large neighborhood search techniques and knapsack heuristics, that has been specifically designed and implemented to solve daily planning problem instances. We conclude with experiment reports and directions for further improvements

Adapting a parallel sparse direct solver to SMP architectures

We consider the direct solution of general sparse linear systems based on a multifrontal method. The approach combines partial static scheduling of the task dependency graph during the symbolic factorization and distributed dynamic scheduling during the numerical factorization to equilibrate work among the processes of a distributed memory computer. We show that to address SMP architectures, and more generally non-uniform memory access multiprocessors, our algorithms for both the static and the dynamic scheduling need to be revisited in order to take account of the non-uniform cost of communication. The performance analysis on an IBM SP with 16 processors per SMP node and up to 128 processors shows that we can signi cantly reduce both the amount of inter-node communication and the solution time

Allocation of Downlink Windows for a Constellation of Satellites

This paper considers the problem of allocation of downlink windows for a constellation of satellites whose mission is to perform a regular surveillance of ship movements over all the oceans. This surveillance is realized using both radar acquisitions of specific areas and acquisition flows continuously collected over the whole orbits. These acquisitions must be downloaded as quickly as possible, to reduce the so-called age of information and improve situation awareness on ground. The paper presents a mathematical modeling of the downlink windows allocation problem in this context, problem decomposition techniques that reduce complexity, and some first experiments on practical instances

[¹¹¹In-DTPA-D-Phe¹]-octreotide, a potential radiopharmaceutical for imaging of somatostatin receptor-positive tumors:synthesis, radiolabeling and in vitro validation

Somatostatin receptor-positive human tumors can be detected using radioiodinated analogues of somatostatin, both in vitro and in vivo. [123I-Tyr3]-octreotide has been successfully used in the visualization of somatostatin receptor-positive tumors by gamma camera scintigraphy, but this radiopharmaceutical has some major drawbacks, which can be overcome with other radionuclides such as 111In. As starting material for a potentially convenient radiopharmaceutical, a diethylenetriaminopentaacetic acid (DTPA) conjugated derivative of octreotide (SMS 201-995) was prepared. This peptide, [DTPA-D-Phe1]-octreotide (SDZ 215-811) binds more than 95 % of added 111In in an easy, single-step labeling procedure without necessity of further purification. The specific somatostatin-like biologic effect of these analogues was proven by the inhibition of growth hormone secretion by cultured rat pituitary cells in a dose-dependent fashion by octreotide, [DTPA-D-Phe1]-octreotide and non-radioactive [115In-DTPA-D-Phe1]-octreotide. The binding of [111In-DTPA-D-Phe1]-octreotide to rat brain cortex membranes proved to be displaced similarly by natural somatostatin as well as by octreotide, suggesting specific binding of [111In-DTPA-D-Phe1]-octreotide to somatostatin receptors. The binding of the indium-labeled compound showed a somewhat lower affinity when compared with the iodinated [Tyr3]-octreotide, but indium-labeled [DTPA-D-Phe1]-octreotide still binds with nanomolar affinity. In conjunction with in vivo studies, these results suggest that [111In-DTPA-D-Phe1]-octreotide is a promising radiopharmaceutical for scintigraphic imaging of somatostatin receptor-positive tumors.</p