SUBROUTINE PHI(TIME, TSTAR, SI, NS, II, M, A2, S, T, OPHI)

C     + + + PURPOSE + + +
C
C     SEE SUBROUTINE PSIS, SINCE PHI(T)=PSI(T,0), FOR COMMENTS
C
C     CALLED FROM HDEPTH
C     AUTHOR(S): D. FLANAGAN, J. ASCOUGH
C     VERSION: THIS MODULE TAKEN FROM ASCOUGH STANDALONE IRS CODE
C     DATE CODED:  3-28-2005
C     CODED BY: D. FLANAGAN
C
C     + + + PARAMETER DECLARATIONS + + +
C
      INTEGER MXTIME
      PARAMETER (MXTIME = 1000)
C
C     + + + ARGUMENT DECLARATIONS + + +
C
      INTEGER NS, II
      REAL TSTAR, SI(MXTIME+1), M, A2, S(MXTIME), T(MXTIME), OPHI
      DOUBLE PRECISION TIME
C
C     + + + ARGUMENT DEFINITIONS + + +
C
C     NS      -
C     II      -
C     TIME    -
C     TSTAR   -
C     SI      -
C     M       -
C     A2      -
C     OPHI    -
C
C     + + + LOCAL VARIABLES + + +
C
      INTEGER K, IU
      REAL B, S1TOM, S2TOM, OSINT

C     + + + END SPECIFICATIONS + + +

C
      IF (TIME.GE.TSTAR) THEN
         B = SI(NS+1)
         IU = NS + 1
      ELSE
         CALL SINT(TIME, T, TSTAR, II, S, SI, NS, OSINT)
         B = OSINT      
         IU = II + 1
      END IF
C     
      K = 2
      OPHI = 0.D0
      S1TOM = 0.D0
C     
   10 IF (K.NE.IU) THEN
         S2TOM = SI(K) ** M
         OPHI = OPHI + (S2TOM-S1TOM) / S(K-1)
         S1TOM = S2TOM
         K = K + 1
         GO TO 10
      END IF
C     
      IF (TIME.LE.TSTAR) THEN
        OPHI = (OPHI+(B**M-S1TOM)/S(K-1)) / M
      ELSE
        OPHI = OPHI + B ** A2 * (TIME-TSTAR)
      END IF
C
      RETURN
      END