!
! This program written by Clint Whaley for CS 1073.  It is an optional
! programming exercise given on 10/08/09.
!
PROGRAM series3
!
!  This program prints out all entries in a series up to and including N,
!  using the series definition:
!    S(i) = S(i-1)*S(i-2) + S(i-3)
!  The user is prompted for N and the seed values S(0), S(1), and S(2)
!
   IMPLICIT NONE
   INTEGER :: i, N
   DOUBLE PRECISION :: Smin3, Smin2, Smin1, S
!
!  Prompt user for series number and seed values.
!
   PRINT *, 'Please enter the last sequence number (>= 0) to compute'
   READ *, N
   PRINT *, 'Please enter S0 S1 and S2 (separated by spaces)'
   READ *, Smin3, Smin2, Smin1
!
!  Do some basic error checking on numbers
!
   IF (N .LT. 0) THEN
      PRINT *, 'Negative N not allowed!'
      STOP
   END IF
   WRITE(*,1000) 0, Smin3
   IF (N .EQ. 0) STOP

   WRITE(*,1000) 1, Smin2
   IF (N .EQ. 1) STOP

   WRITE(*,1000) 2, Smin1
   IF (N .EQ. 2) STOP
!
!  Print the I=3 to N entries in the sequence
!
   DO i = 3, N
      S = Smin1*Smin2 + Smin3
      WRITE(*,1000) i, S
      Smin3 = Smin2
      Smin2 = Smin1
      Smin1 = S
   END DO

1000 FORMAT('S', I3.3, ' = ', ES17.10)

END PROGRAM series3