Editing Pathological (mathematics) (section)

==Computer science==
In [[computer science]], ''pathological'' has a slightly different sense with regard to the study of [[algorithm]]s. Here, an input (or set of inputs) is said to be ''pathological'' if it causes atypical behavior from the algorithm, such as a violation of its average case [[Computational complexity theory|complexity]], or even its correctness. For example, [[hash table]]s generally have pathological inputs: sets of keys that [[Hash collision|collide]] on hash values. [[Quicksort]] normally has <math>O(n \log{n})</math> time complexity, but deteriorates to <math>O(n^2)</math> when it is given input that triggers suboptimal behavior.

The term is often used pejoratively, as a way of dismissing such inputs as being specially designed to break a routine that is otherwise sound in practice (compare with ''[[Byzantine failure|Byzantine]]''). On the other hand, awareness of pathological inputs is important, as they can be exploited to mount a [[denial-of-service attack]] on a computer system. Also, the term in this sense is a matter of subjective judgment as with its other senses. Given enough run time, a sufficiently large and diverse user community (or other factors), an input which may be dismissed as pathological could in fact occur (as seen in the [[Ariane 5 Flight 501|first test flight]] of the [[Ariane 5]]).