[$] Plotting tools for networks, part I

In the first two installments in this series on plotting tools(which covered gnuplot and matplotlib), we introduced tools for creating plots and graphs, and used the termsinterchangeably to refer to the typical scientific plot relating oneset of quantities to another. In this article we use the term "graph"in its mathematical, graph-theory context, meaning a set of nodes connected byedges. There is a strong family resemblance among graph-theory graphs,flowcharts, and network diagrams-so much so that some of the sametools can be coerced into creating all of them. We will now surveyseveral mature free-software systems for building these typesof visualizations. At least one of these tools will likely be useful if youare ever in need of an automated way to diagram source-codeinterdependencies, make an organizational chart, visualize a computernetwork, or organize a sports tournament. We will start with agraphical charting tool and a flexible graphing system that can easily be called by other programs.