cray instability: n. 1. A shortcoming of a program or algorithm
that manifests itself only when a large problem is being run on a
powerful machine (see cray). Generally more subtle than bugs that
can be detected in smaller problems running on a workstation or
mini. 2. More specifically, a shortcoming of algorithms which are
well behaved when run on gentle floating point hardware (such as
IEEE-standard or PDP-series machines) but which break down badly
when exposed to a Cray's unique `rounding' rules.