<p class="MsoNormal" style="text-align: left; margin: 0cm 0cm 0pt; layout-grid-mode: char;" align="left"><span class="text"><span style="font-family: ";Arial";,";sans-serif";; font-size: 9pt;">In this paper we propose a distributed algorithm for solving the positioning problem in ad-hoc wireless networks. The method is based on the capability of the nodes to measure the angle of arrival (AOA) of the signals they produce. The main features of the distributed algorithm are simplicity, asynchronous operations (i.e. no global coordination among nodes is required), ability to operate in disconnected networks. Moreover each node can join the computation at any time. Numerical results, obtained by simulating several scenarios, show that the algorithm can reach a good level of convergence even when the number of communications is limited.</span></span><span style="font-family: ";Arial";,";sans-serif";; font-size: 9pt;"></span></p>

<p class="MsoNormal" style="text-align: left; margin: 0cm 0cm 0pt; layout-grid-mode: char;" align="left"><span class="text"><span style="font-family: ";Arial";,";sans-serif";; font-size: 9pt;">In this paper, we study the dynamic version of the distributed all-pairs shortest paths problem. Most of the solutions given in the literature for this problem, either (i) work under the assumption that before dealing with an edge operation, the algorithm for the previous operation has to be terminated, that is, they are not able to update shortest paths concurrently, or (ii) concurrently update shortest paths, but their convergence can be very slow (possibly infinite). In this paper we propose a partially dynamic algorithm that overcomes most of these limitations. In particular, it is able to concurrently update shortest paths and in many cases its convergence is quite fast. These properties are highlighted by an experimental study whose aim is to show the effectiveness of the proposed algorithms also in the practical case.</span></span><span style="font-family: ";Arial";,";sans-serif";; font-size: 9pt;"></span></p>

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The experience described in this paper relates to the implementation on the parallel computer APEmille of a model for large-scale atmosphere motion, originally developed in Fortran for a conventional architecture. The most critical aspects of this work are described: the mapping of a bidimensional problem on the tridimensional thoroidal architecture of the parallel machine, the choice of a data distribution strategy that minimizes the internode communication needs, the definition of an algorithm for internode communication that minimizes communication costs by performing only first neighbour communications, and the implementation of machine dependant optimizations that allowed to exploit the pipelined architecture of the APEmille processing node and the large register file. An analysis of the performances is reported, compared to both the APEmille peak performance and to the performance on other conventional sequential architectures. Finally, a comparison with the original physical results is presented.