PROGRAM series1
!
! Author:  Br. David Carlson
!
! Date:  December 31, 1999
!
! Revised:  May 2, 2004
!
! This program prints out partial sums for a series, stopping when no further
! change is found by adding on another term (or when a set number of terms
! have been added -- to prevent an infinite loop).  The particular series used
! is 1 + 1/2 + 1/4 + 1/8 + ...

IMPLICIT NONE

REAL::term, sum, sumold
INTEGER::n

term = 1.0
sum = 0.0
n = 0

WRITE (*, 20)
20 FORMAT (1X, 'Program to investigate a series')
WRITE (*, 50)
50 FORMAT (' ', T5, 'n', T15, 'term', T35, 'partial sum')

DO 
   n = n + 1
   sumold = sum
   sum = sum + term
   WRITE (*, 100) n, term, sum
   IF ((sum == sumold) .OR. (n == 200)) THEN
      EXIT
   END IF
   term = term * 0.5
END DO

100 FORMAT (' ', T5, I3, T15, E16.8, T35, E16.8)

END PROGRAM