I'm not sure I completely understand what you need, but you might try   
   gaussian distribution or gaussian curve (german mathematician Johann   
   Gauss).   
      
   [ comp.ai is moderated.  To submit, just post and be patient, or if ]   
   [ that fails mail your article to , and ]   
   [ ask your news administrator to fix the problems with your system. ]   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)