C     -*-fortran-*-
C     A.-H. DISPERSION CURVES
C     THIS CALCULATES THE SQUARES OF THE REFRACTIVE
C     INDEX WITH THE PLUS/MINUS SIGNS.  NO ATTEMPT IS
C     MADE TO DETERMINE ORDINARY, EXTRAORDINARY RAYS
C
      IMPLICIT NONE
		     
      REAL X,XMIN,XMAX,DELX,YL,YT,Z 
      COMPLEX J,BR,DENP,DENM,N2P,N2M

      J=(0,1.0) 

      OPEN (UNIT=8,FILE='ah_out.dat',STATUS='NEW') 
      write(*,*)'INPUT YL,YT,Z'
      READ (5,*) YL,YT,Z 
      write(*,*)'INPUT XMIN,XMAX,DEL'
      READ (5,*) XMIN,XMAX,DELX 
      X=XMIN 
      DO 100 WHILE (X.LE.XMAX) 
      IF (X-1.0) 2,3,2 
    3 X=0.9999 
    2 CONTINUE 
      BR=0.5*YT**2/(1-X-J*Z) 
      DENP=1-J*Z-BR+CSQRT(BR**2+YL**2) 
      DENM=1-J*Z-BR-CSQRT(BR**2+YL**2) 
      N2P=1-X/DENP 
      N2M=1-X/DENM 
      WRITE (8,220) X,N2P,N2M 
  220 FORMAT(5F10.4) 
      X=X+DELX 
  100 CONTINUE 
   50 STOP 
      END