cray instability

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 DEC) but which break down badly
   when exposed to a Cray's unique `rounding' rules.