ADAS Subroutine yip

       FUNCTION YIP(XI,DELTA)                                 
C
       IMPLICIT REAL*8 (A-H,O-Z)                             
C
C-----------------------------------------------------------------------
C
C  ****************** FORTRAN77 FUNCTION: YIP **************************
C
C PURPOSE UNKNOWN
C
C NOTES: THIS ROUTINE IS NOT YET PROPERLY ANNOTATED
C
C UNIX-IDL PORT:
C
C VERSION: 1.1                          DATE: 16-1-96
C MODIFIED: TIM HAMMOND (TESSELLA SUPPORT SERVICES PLC)
C               - FIRST VERSION
C
C-----------------------------------------------------------------------
C
      REAL*8              DELTA,       XI