Algorithms in computational geometry often use the real-RAM model of computation. This model assumes that exact real numbers can be stored in memory and retreived in constant time, and that field operations (+,-, *, /) and certain other operations, square root, sine, and cosine for instance, are exact, and can be applied in constant time. These assumptions are often difficult to discharge at implementation time. Even well-understood algorithms, like line-sweep for polygon union [PS85], present much trouble. Why? Such algorithms obtain good combinatorial complexity bounds by exploiting geometric orders on the input. These relations are often implicit, so an algorithm can only probe them pointwise with a collection of predicate functions answering, e.g., "Is point p left of edge e?". In implementations, the reply must depend on arithmetic with finitely represented numbers. The trouble originates here.

The West Point Bridge Design Contest is a nationwide competition intended to increase middle school and high school students' interest in engineering. Unique among national engineering competitions, it entails no cost to participants, is entirely Internet‐based, and is achievable by any student with a Web‐enabled computer. By leveraging information technology, a project team of just three people has provided an engaging engineering design experience to over 30,000 students in the past two years. The project receives financial and promotional support from the American Society of Civil Engineers and private industry. Feedback from contestants and teachers indicates that students' interest in engineering is positively affected by their participation in the contest.