Uniquely Restricted Matchings

A matching in a graph is a set of edges no two of which share a common vertex. In this paper we introduce a new, specialized type of matching which we call uniquely restricted matchings, originally motivated by the problem of determining a lower bound on the rank of a matrix having a specified zero/ non-zero pattern. A uniquely restricted matching is defined to be a matching M whose saturated vertices induce a subgraph which has only one perfect matching, namely M itself. We introduce the two problems of recognizing a uniquely restricted matching and of finding a maximum uniquely restricted matching in a given graph, and present algorithms and complexity results for certain special classes of graphs. We demonstrate that testing whether a given matching M is uniquely restricted can be done in O(|M||E|) time for an arbitrary graph G=(V,E) and in linear time for cacti, interval graphs, bipartite graphs, split graphs and threshold graphs. The maximum uniquely restricted matching problem is shown to be NP-complete for bipartite graphs, split graphs, and hence for chordal graphs and comparability graphs, but can be solved in linear time for threshold graphs, proper interval graphs, cacti and block graphs. Received April 12, 1998; revised June 21, 1999.     

Writing Code to Prototype, Ideate, and Discover

Programmers often write code to prototype, ideate, and discover. To do this, they work opportunistically, emphasizing speed and ease of development over code robustness and maintainability. How do opportunistic programmers make these trade-offs, and how does their work's structure compare to more formal software engineering practices? Opportunistic programmers build software using high-level tools and often add new functionality via copy-and-paste from the Web. They iterate rapidly, consider code impermanent, and find debugging particularly challenging. Five opportunistic-programming principles can help guide the development of tools that explicitly support prototyping in code.     

Media discourse on ageing water infrastructure

Urban infrastructure in the United States is ageing, but media portrayal of this phenomena has been insufficient. Failures such as water main breaks are a daily occurrence in many cities. In addition, citizens are regularly reminded of the costs through increases in water and sewer rates. To explore media discourse on this issue, a content analysis of print media articles on water main breaks (Breaks), and water and sewer rate increases (Rates) for the period 1999–2012 was conducted. The analysis of approximately 500 randomly drawn articles on each topic found that media coverage of water infrastructure is an episodic affair with little attention to ongoing issues. Rates articles contained more details and a focus on governance, while Breaks articles addressed business concerns and were concentrated in older cities. The article concludes that media stories are not providing sufficient information to serve the needs of democratic governance of urban infrastructure issues.