C FPLQ5     SOURCE    CHAT      05/01/13    00:07:39     5004
      FUNCTION FPLQ5(X,COST,Z,RHO)
      IMPLICIT INTEGER(I-N)
      IMPLICIT REAL*8 (A-H,O-Z)
      D2=X**2+Z**2
      XCOS=X*COST
      XRCOS=RHO*XCOS
      C=SQRT(D2-2.*XRCOS+RHO**2)
      FPLQ5=C+XCOS*LOG(C+RHO-XCOS)
      RETURN
      END