= Ruby Graph Library (RGL) RGL is a framework for graph data structures and algorithms. The design of the library is much influenced by the Boost Graph Library (BGL) which is written in C++ heavily using its template mechanism. Refer to http://www.boost.org/libs/graph/doc for further links and documentation on graph data structures and algorithms and the design rationales of BGL. A comprehensive summary of graph terminology can be found in the the graph section of the Dictionary of Algorithms and Data Structures at http://www.nist.gov/dads/HTML/graph.html. == Design principles This document concentrates on the special issues of the implementation in Ruby. The main design goals directly taken from the BGL design are: * An interface for how the structure of a graph can be accessed using a generic interface that hides the details of the graph data structure implementation. This interface is defined by the module Graph, which should be included in concrete classes. * A standardized generic interface for traversing graphs (RGL::GraphIterator) RGL provides some general purpose graph classes that conform to this interface, but they are not meant to be the *only* graph classes. As in BGL I believe that the main contribution of the RGL is the formulation of this interface. The BGL graph interface and graph components are generic in the sense of the C++ Standard Template Library (STL). In Ruby other techniques are available to express the generic character of the algorithms and data structures mainly using mixins and iterators. The BGL documentation mentions three means to achieve genericity: * Algorithm/Data-Structure Interoperability * Extension through Function Objects and Visitors * Element Type Parameterization * Vertex and Edge Property Multi-Parameterization The first is easily achieved in RGL using mixins, which of course is not as efficient than C++ templates (but much more readable :-). The second one is even more easily implemented using standard iterators with blocks or using the Stream module. The third one is no issue since Ruby is dynamically typed: Each object can be a graph vertex. There is no need for a vertex (or even edge type). In the current version of RGL properties of vertices are simply attached using hashes. At first there seems to be not much need for the graph property machinery. === Algorithms The first version of RGL only contains a core set of algorithm patterns: * Breadth First Search (RGL::BFSIterator) * Depth First Search (RGL::DFSIterator) The algorithm patterns by themselves do not compute any meaningful quantities over graphs, they are merely building blocks for constructing graph algorithms. The graph algorithms in RGL currently include: * Topological Sort (RGL::TopsortIterator) * Connected Components (RGL::Graph#each_connected_component) * Strongly Connected Components (RGL::Graph#strongly_connected_components) * Transitive Closure (RGL::Graph#transitive_closure) === Data Structures RGL currently provides two graph classes that implement a generalized adjacency list and an edge list adaptor. * RGL::AdjacencyGraph * RGL::ImplicitGraph The AdjacencyGraph class is the general purpose *swiss army knife* of graph classes. It is highly parameterized so that it can be optimized for different situations: the graph is directed or undirected, allow or disallow parallel edges, efficient access to just the out-edges, fast vertex insertion and removal at the cost of extra space overhead, etc. === Differences to BGL The concepts of IncidenceGraph, AdjacencyGraph and VertexListGraph (see http://www.boost.org/libs/graph/doc/IncidenceGraph.html) are here bundled in the base graph module. Most methods of IncidenceGraph should be standard in the base module Graph. The complexity guarantees can not necessarily provided. See http://www.boost.org/libs/graph/doc/graph_concepts.html == Installation RGL is depended on the _stream_ library which can also be downloaded from http://rubyforge.org/frs/?group_id=110. === GEM Installation Download the GEM file and install it with .. gem install rgl-VERSION.gem or directly with gem install rgl Use the correct version number for VERSION (e.g. 0.2.2). You may need root privileges to install. === Normal Installation You have to install stream library before. You can than install RGL with the following command: % ruby install.rb from its distribution directory. == Example irb session with RGL irb> require 'rgl/adjacency' irb> dg=RGL::DirectedAdjacencyGraph[1,2 ,2,3 ,2,4, 4,5, 6,4, 1,6] # Use DOT to visualize this graph: irb> require 'rgl/dot' irb> dg.write_to_graphic_file('jpg') "graph.jpg" The result: link:../examples/example.jpg irb> dg.directed? true irb> dg.vertices [5, 6, 1, 2, 3, 4] irb> dg.has_vertex? 4 true Every object could be a vertex (there is no class Vertex), even the class object _Object_: irb> dg.has_vertex? Object false irb> dg.edges.sort.to_s "(1-2)(1-6)(2-3)(2-4)(4-5)(6-4)" irb> dg.to_undirected.edges.sort.to_s "(1=2)(1=6)(2=3)(2=4)(5=4)(6=4)" Add inverse edge (4-2) to directed graph: irb> dg.add_edge 4,2 (4-2) == (2-4) in the undirected graph: irb> dg.to_undirected.edges.sort.to_s "(1=2)(1=6)(2=3)(2=4)(5=4)(6=4)" (4-2) != (2-4) in directed graphs: irb> dg.edges.sort.to_s "(1-2)(1-6)(2-3)(2-4)(4-2)(4-5)(6-4)" irb> dg.remove_edge 4,2 true Topological sort is realized with as iterator: require 'graph/traversal' irb> dg.topsort_iterator.to_a [1, 2, 3, 6, 4, 5] A more elaborated example showing implicit graphs: def module_graph RGL::ImplicitGraph.new { |g| g.vertex_iterator { |b| ObjectSpace.each_object(Module, &b) } g.adjacent_iterator { |x, b| x.ancestors.each { |y| b.call(y) unless x == y || y == Kernel || y == Object } } g.directed = true } end This function creates a directed graph with vertices being all loaded modules: g = module_graph We only want to see the ancestors of RGL::AdjacencyGraph: tree = bfs_search_tree_from(g,RGL::AdjacencyGraph) Now we want to visualize this component of g with DOT. We therefore create a subgraph of the original graph using a filtered graph: g = g.vertices_filtered_by {|v| tree.has_vertex? v} Create the graphics with DOT: g.write_to_graphic_file produces module_graph.jpg: link:../examples/module_graph.jpg Look for more in the examples directory (i.e. examples.rb[link:files/examples/examples_rb.html]). == Credits Many thanks to Robert Feldt which also worked on a graph library (http://rockit.sf.net/subprojects/graphr) who pointed me to BGL and many other graph resources. Manuel Simoni found a subtle bug in a preliminary version announced at http://rubygarden.com/ruby?RubyAlgorithmPackage/Graph. Robert kindly allowed to integrate his work on graphr, which I did not yet succeed. Especially his work to output graphs for GraphViz (see http://www.research.att.com/sw/tools/graphviz/download.html) is much more elaborated than the minimal support in dot.rb. Jason Voegele for set.rb implementing sets using hashes. These are used in the implementation of adjacency lists in AdjacencyGraph. Jeremy Siek one of the authors of the nice book "The Boost Graph Library (BGL)" (http://cseng.awl.com/book/0,3828,0201729148,00.html) kindly allowed to use the BGL documentation as a _cheap_ reference for RGL. He and Robert also gave feedback and many ideas for RGL. Dave Thomas for RDoc (http://rdoc.sourceforge.net) which generated what you read and matz for Ruby. Dave included in the latest version of RDoc (alpha9) the module dot/dot.rb which I use instead of Roberts module to visualize graphs (see rgl/dot.rb). == Copying RGL is Copyright (c) 2002,2004 by Horst Duchene. It is free software, and may be redistributed under the terms specified in the README file of the Ruby distribution. == Support Please contact me at mailto:monora@users.sourceforge.net with bug reports suggestions, and other comments. If you send patches, it would help if they were in-line (not attachments) and generated using "diff -u".