FUNCTION XNORM(ALF,XMEAN,SIG)                                             
C   COMPUTES THE PERCENTILES OF THE NORMAL DISTRIBUTION N(XMEAM,SIG)            
C   PARAMETERS                                                                  
C     ALF - PROBABILITY INTEGRAL FROM NEGATIVE INFINITY TO XNORM                
C     XMEAN - POPULATION MEAN                                                   
C     SIG - POPULATION STANDARD DEVIATION                                       
C     XNORM - COPMUTED ABSCISSA VALUE OF N(XMEAN,SIG) CORRESPONDING TO          
C             PROBABILITY ALF                                                   
C ACCURACY BETTER THAN THAN 0.00045                                         0120
      IMPLICIT REAL*8(A-H,O-Z)                                              0130
      DIMENSION C(6)                                                        0140
      DATA C/2.515517D0,0.802853D0,0.010328D0,1.432788D0,0.189269D0,        0150
     *  0.001308D0/                                                         0160
      IF(ALF .GE. 1D0 .OR. ALF .LE. 0D0) GO TO 20                           0170
      SIGN = -1.                                                            0180
      P = ALF                                                               0190
      IF(ALF .LT. 0.5D0) GO TO 10                                           0200
      SIGN = 1.                                                             0210
      P = 1. - ALF                                                          0220
   10 T = DSQRT(DLOG(1./P**2))                                              0230
      T2 = T * T                                                            0240
      T3 = T * T2                                                           0250
      XP = T - (C(1)+C(2)*T+C(3)*T2) / (1.+C(4)*T+C(5)*T2+C(6)*T3)          0260
      XP = XP * SIGN                                                        0270
      XNORM = XMEAN + XP * SIG                                              0280
      RETURN                                                                0290
   20 WRITE(6,1001) ALF                                                     0300
 1001 FORMAT(10X,'XNORM INPUT PROBABILITY=',E20.10)                         0310
      XNORM = 0.                                                            0320
      RETURN                                                                0330
      END                                                                   0340