SUBROUTINE ELI1(RES,TH,EM)
	CK=SQRT(ABS(1.-EM**2))
	IF(ABS(EM).GT.1.0) CK=-CK
	IF(ABS(COS(TH)).LT..1E-5) GO TO 116
	X=SIN(TH)/COS(TH)
	GO TO 17
116	X=.1E10*SIN(TH)/ABS(SIN(TH))
17      IF(X) 2,1,2
 1    RES=0.
      RETURN
 2    IF(CK) 4,3,4
 3    RES=ALOG(ABS(X)+SQRT(ABS(1.+X*X)))
      GO TO 13
 4    ANGLE=ABS(1.0/X)
      GEC=ABS(CK)
      ARI=1.
      PIM=0.
 5    SQGEC=ARI*GEC
      AARI=ARI
      ARI=GEC+ARI
      ANGLE= -SQGEC/ANGLE+ANGLE
      SQGEC=SQRT(ABS(SQGEC))
      IF(ANGLE) 7,6,7
C---- REPLACE 0. BY A SMALL VALUE
 6    ANGLE=SQGEC*1.E-8
 7    TEST=AARI*1.E-4
      IF(ABS(AARI-GEC)-TEST) 10,10,8
 8    GEC=SQGEC+SQGEC
      PIM=PIM+PIM
      IF(ANGLE) 9,5,5
 9    PIM=PIM+3.1415927
      GO TO 5
 10   IF(ANGLE) 11,12,12
 11   PIM=PIM+3.1415927
 12   RES=(ATAN(ARI/ANGLE)+PIM)/ARI
13	IF(X) 14,15,15
14	RES=-RES
 15   RETURN
      END