61640852
Saturation NOW
We present a distributed version of the saturation algorithm for symbolic state-space generation of discrete-state models. The execution is strictly sequential but utilizes the overall available memory. A level-based allocation of the decision diagram nodes onto the workstations is created. No additional node or work is created. A dynamic memory load balancing heuristic helps coping with the uneven growth of the decision diagram levels allocated to each workstation. Experiments on a conventional network of workstations show that the runtime of our distributed implementation is close to the sequential one even when balancing is triggered, while it is of course much better when the sequential implementation is forced to rely on virtual memory.
6519527
A dynamic firing speculation to speedup distributed symbolic state-space generation
The saturation strategy for symbolic state-space generation is very effective for globally-asynchronous locally-synchronous discrete-state systems. Its inherently sequential nature, however, makes it difficult to parallelize on a NOW. An initial attempt that utilizes idle workstations to recognize event firing patterns and then speculatively compute firings conforming to these patterns is at times effective but can introduce large memory overheads. We suggest an implicit method to encode the firing history of decision diagram nodes, where patterns can be shared by nodes. By preserving the actual firing history efficiently and effectively, the speculation is more informed. Experiments show that our implicit encoding method not only reduces the memory requirements but also enables dynamic speculation schemes that further improve runtime
229363
A Pattern Recognition Approach for Speculative Firing Prediction in Distributed Saturation State-Space Generation
The saturation strategy for symbolic state-space generation is particularly effective for globally-asynchronous locally-synchronous systems. A distributed version of saturation, SaturationNOW, uses the overall memory available on a network of workstations to effectively spread the memory load, but its execution is essentially sequential. To achieve true parallelism, we explore a speculative firing prediction, where idle workstations work on predicted future event firing requests. A naive approach where all possible firings may be explored a priori, given enough idle time, can result in excessive memory requirements. Thus, we introduce a history-based approach for firing prediction that recognizes firing patterns and explores only firings conforming to these patterns. Experiments show that our heuristic improves the runtime and has a small memory overhead.
206929044
Comparison of structural formalisms for modeling large Markov models
Summary form only given. Stochastic automata networks and generalized stochastic Petri nets are the main formalisms used to model complex Markov systems in a structured "Kronecker" approach. We compare them on a suite of examples using two tools, PEPS and SMART.
6697965
A Fine-Grained Fullness-Guided Chaining Heuristic for Symbolic Reachability Analysis
Chaining can reduce the number of iterations required for symbolic state-space generation and model-checking, especially in Petri nets and similar asynchronous systems, but requires considerable insight and is limited to a static ordering of the events in the high-level model. We introduce a two-step approach that is instead fine-grained and dynamically applied to the decision diagrams nodes. The first step, based on a precedence relation, is guaranteed to improve convergence, while the second one, based on a notion of node fullness, is heuristic. We apply our approach to traditional breadth-first and saturation state-space generation, and show that it is effective in both cases.
850145
Multiple sequence alignment using simulated annealing
Multiple sequence alignment is a useful technique for studying molecular evolution and analyzing structure-sequence relationships. Dynamic programming of multiple sequence alignment has been widely used to find an optimal alignment. However, dynamic programming does not allow for certain types of gap costs, and it limits the number of sequences that can be aligned due to its high computational complexity. The focus of this paper is to use simulated annealing as the basis for developing an efficient multiple sequence alignment algorithm. An algorithm called Multiple Sequence Alignment using Simulated Annealing (MSASA) has been developed. The computational complexity of MSASA is significantly reduced by replacing the high-temperature phase of the annealing process by a fast heuristic algorithm. This heuristic algorithm facilitates in minimizing the solution set of the low-temperature phase of the annealing process. Compared to the dynamic programming approach, MSASA can (i) use natural gap costs which can generate better solution, (ii) align more sequences and (iii) take less computation time.
92691
A Formal Approach to Managing Design Processes
To capture market opportunities, competition within the microelectronics industry demands ever-faster product development, which means ever-shorter design cycles. Shorter design cycles can be achieved by carefully managing the design process during rapid prototyping. Careful management is important because the design process must be (1) adjusted to accommodate constraints such as product performance and design time, and (2) frequently updated to take advantage of new design tools and methodologies. Traditionally, designers have used whatever tools seemed convenient to them at the time, which has made it virtually impossible to determine what methodology was used to produce a given design. These problems can be avoided through design methodology management, which ensures that appropriate tools are selected and executed in the appropriate sequence. Effective design management requires an environment equipped with a formal representation of supported design processes and tools, and an execution environment that helps designers select and execute an appropriate design process. We propose a methodology management system that provides this functionality. >
17772071
Large 2P3-free graphs with bounded degree
Abstract Let ex ∗ ( D ; H ) be the maximum number of edges in a connected graph with maximum degree D and no induced subgraph H ; this is finite if and only if H is a disjoint union of paths. If the largest component of such an H has order m , then ex ∗ (D; H) = O (D 2 ex ∗ (D; P m )) . Constructively, ex ∗ (D;qP m ) = Θ( g D 2 ex ∗ (D;P m )) if q >1 and m > 2( Θ ( gD 2 ) if m = 2). For H = 2 P 3 (and D ⩾ 8), the maximum number of edges is 1 8 [D 4 + D 3 + D 2 + 6D] if D is even and 1 8 [D 4 + D 3 + 2D 2 + 3D + 1 ] if D is odd, achieved by a unique extremal graph.