3,320 research outputs found
Graph Interpolation Grammars as Context-Free Automata
A derivation step in a Graph Interpolation Grammar has the effect of scanning
an input token. This feature, which aims at emulating the incrementality of the
natural parser, restricts the formal power of GIGs. This contrasts with the
fact that the derivation mechanism involves a context-sensitive device similar
to tree adjunction in TAGs. The combined effect of input-driven derivation and
restricted context-sensitiveness would be conceivably unfortunate if it turned
out that Graph Interpolation Languages did not subsume Context Free Languages
while being partially context-sensitive. This report sets about examining
relations between CFGs and GIGs, and shows that GILs are a proper superclass of
CFLs. It also brings out a strong equivalence between CFGs and GIGs for the
class of CFLs. Thus, it lays the basis for meaningfully investigating the
amount of context-sensitiveness supported by GIGs, but leaves this
investigation for further research
Building a Truly Distributed Constraint Solver with JADE
Real life problems such as scheduling meeting between people at different
locations can be modelled as distributed Constraint Satisfaction Problems
(CSPs). Suitable and satisfactory solutions can then be found using constraint
satisfaction algorithms which can be exhaustive (backtracking) or otherwise
(local search). However, most research in this area tested their algorithms by
simulation on a single PC with a single program entry point. The main
contribution of our work is the design and implementation of a truly
distributed constraint solver based on a local search algorithm using Java
Agent DEvelopment framework (JADE) to enable communication between agents on
different machines. Particularly, we discuss design and implementation issues
related to truly distributed constraint solver which might not be critical when
simulated on a single machine. Evaluation results indicate that our truly
distributed constraint solver works well within the observed limitations when
tested with various distributed CSPs. Our application can also incorporate any
constraint solving algorithm with little modifications.Comment: 7 page
Dynamic Dominators and Low-High Orders in DAGs
We consider practical algorithms for maintaining the dominator tree and a low-high order in directed acyclic graphs (DAGs) subject to dynamic operations. Let G be a directed graph with a distinguished start vertex s. The dominator tree D of G is a tree rooted at s, such that a vertex v is an ancestor of a vertex w if and only if all paths from s to w in G include v. The dominator tree is a central tool in program optimization and code generation, and has many applications in other diverse areas including constraint programming, circuit testing, biology, and in algorithms for graph connectivity problems. A low-high order of G is a preorder of D that certifies the correctness of D, and has further applications in connectivity and path-determination problems.
We first provide a practical and carefully engineered version of a recent algorithm [ICALP 2017] for maintaining the dominator tree of a DAG through a sequence of edge deletions. The algorithm runs in O(mn) total time and O(m) space, where n is the number of vertices and m is the number of edges before any deletion. In addition, we present a new algorithm that maintains a low-high order of a DAG under edge deletions within the same bounds. Both results extend to the case of reducible graphs (a class that includes DAGs). Furthermore, we present a fully dynamic algorithm for maintaining the dominator tree of a DAG under an intermixed sequence of edge insertions and deletions. Although it does not maintain the O(mn) worst-case bound of the decremental algorithm, our experiments highlight that the fully dynamic algorithm performs very well in practice. Finally, we study the practical efficiency of all our algorithms by conducting an extensive experimental study on real-world and synthetic graphs
Board of Directors Meeting Minutes (November 7, 1989)
This file contains the minutes from the Des Moines Area Community College Board meeting held on November 7, 1989
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