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pathological: adj. 1. [scientific computation] Used of a data set
   that is grossly atypical of normal expected input, esp. one that
   exposes a weakness or bug in whatever algorithm one is using.  An
   algorithm that can be broken by pathological inputs may still be
   useful if such inputs are very unlikely to occur in practice.
   2. When used of test input, implies that it was purposefully
   engineered as a worst case.  The implication in both senses is that
   the data is spectacularly ill-conditioned or that someone had to
   explicitly set out to break the algorithm in order to come up with
   such a crazy example.  3. Also said of an unlikely collection of
   circumstances.  "If the network is down and comes up halfway
   through the execution of that command by root, the system may just
   crash."  "Yes, but that's a pathological case."  Often used to
   dismiss the case from discussion, with the implication that the
   consequences are acceptable, since they will happen so infrequently
   (if at all) that it doesn't seem worth going to the extra trouble
   to handle that case (see sense 1).