function PHINV(P)
!
!     ALGORITHM AS241  APPL. STATIST. (1988) VOL. 37, NO. 3
!
!     Produces the normal deviate Z corresponding to a given lower
!     tail area of P.
!
!     Author: 22 Mar 2004 R. Jones (translated from f95 of A. Gentz)

      implicit double precision (a-h,k-l,o-z)

      parameter( SPLIT1 = 0.425d0, SPLIT2 = 5d0,
     &           CONST1 = 0.180625d0, CONST2 = 1.6d0) 
!     
!     Coefficients for P close to 0.5
!     
      parameter(
     &     A0 = 3.3871328727963666080d00,
     &     A1 = 1.3314166789178437745d+2,
     &     A2 = 1.9715909503065514427d+3,
     &     A3 = 1.3731693765509461125d+4,
     &     A4 = 4.5921953931549871457d+4,
     &     A5 = 6.7265770927008700853d+4,
     &     A6 = 3.3430575583588128105d+4,
     &     A7 = 2.5090809287301226727d+3,
     &     B1 = 4.2313330701600911252d+1,
     &     B2 = 6.8718700749205790830d+2,
     &     B3 = 5.3941960214247511077d+3,
     &     B4 = 2.1213794301586595867d+4,
     &     B5 = 3.9307895800092710610d+4,
     &     B6 = 2.8729085735721942674d+4,
     &     B7 = 5.2264952788528545610d+3 )
!     
!     Coefficients for P not close to 0, 0.5 or 1.
!     
      parameter(
     &     C0 = 1.42343711074968357734d0,
     &     C1 = 4.63033784615654529590d0,
     &     C2 = 5.76949722146069140550d0,
     &     C3 = 3.64784832476320460504d0, 
     &     C4 = 1.27045825245236838258d0,
     &     C5 = 2.41780725177450611770d-1,
     &     C6 = 2.27238449892691845833d-2,
     &     C7 = 7.74545014278341407640d-4,
     &     D1 = 2.05319162663775882187d0,
     &     D2 = 1.67638483018380384940d0,
     &     D3 = 6.89767334985100004550d-1,
     &     D4 = 1.48103976427480074590d-1,
     &     D5 = 1.51986665636164571966d-2,
     &     D6 = 5.47593808499534494600d-4,
     &     D7 = 1.05075007164441684324d-9 )
!
!	Coefficients for P near 0 or 1.
!
      parameter(
     &     E0 = 6.65790464350110377720d0,
     &     E1 = 5.46378491116411436990d0,
     &     E2 = 1.78482653991729133580d0,
     &     E3 = 2.96560571828504891230d-1,
     &     E4 = 2.65321895265761230930d-2,
     &     E5 = 1.24266094738807843860d-3,
     &     E6 = 2.71155556874348757815d-5,
     &     E7 = 2.01033439929228813265d-7,
     &     F1 = 5.99832206555887937690d-1,
     &     F2 = 1.36929880922735805310d-1,
     &     F3 = 1.48753612908506148525d-2,
     &     F4 = 7.86869131145613259100d-4,
     &     F5 = 1.84631831751005468180d-5,
     &     F6 = 1.42151175831644588870d-7,
     &     F7 = 2.04426310338993978564d-15 )
!     
      Q = ( 2*P - 1 )/2
      IF ( ABS(Q) .le. SPLIT1 ) THEN
         R = CONST1 - Q*Q
         PHINV = Q*( ( ( ((((A7*R + A6)*R + A5)*R + A4)*R + A3)
     &                 *R + A2 )*R + A1 )*R + A0 ) 
     &           /( ( ( ((((B7*R + B6)*R + B5)*R + B4)*R + B3)
     &                 *R + B2 )*R + B1 )*R + 1 )
      ELSE
         R = MIN( P, 1 - P )
         IF ( R .gt. 0d0 ) THEN
            R = SQRT( -LOG(R) )
            IF ( R .le. SPLIT2 ) THEN
               R = R - CONST2
               PHINV = ( ( ( ((((C7*R + C6)*R + C5)*R + C4)*R + C3)
     &                     *R + C2 )*R + C1 )*R + C0 ) 
     &               /( ( ( ((((D7*R + D6)*R + D5)*R + D4)*R + D3)
     &                      *R + D2 )*R + D1 )*R + 1 )
            ELSE
               R = R - SPLIT2
               PHINV = ( ( ( ((((E7*R + E6)*R + E5)*R + E4)*R + E3)
     &                     *R + E2 )*R + E1 )*R + E0 )
     &               /( ( ( ((((F7*R + F6)*R + F5)*R + F4)*R + F3)
     &                     *R + F2 )*R + F1 )*R + 1 ) 
            END IF
         ELSE
            PHINV = 9
         END IF
         IF ( Q .lt. 0d0 ) THEN
            PHINV = - PHINV
         END IF
      END IF
!
      RETURN
      end