C     TITLE: THIS DOES LARGEST TO SMALLEST, AND THE REVERSE.
C
      IMPLICIT DOUBLE PRECISION (D)
      DIMENSION A(20000)
C
10    PRINT *, 'HOW MANY TERMS(MAX=20000)?'
      READ *, N
      IF(N .EQ. 0) STOP
C
      DO 20 J=1,N
20      A(J ) = 1.0/J
C
      DTRUE=0.0D0
      DO 21 I=1,N
21      DTRUE = DTRUE + A(I)
      TRUE=DTRUE
C
      SUM=0.0
      DO 22 I=1,N
22      SUM=SUM+A(I)
      ERROR = TRUE-SUM 
C
      PRINT *, 'TRUE=', TRUE
      PRINT *, 'LARGEST TO SMALLEST SUM = ', SUM
      PRINT *, 'ERROR=', ERROR 
C
      SUM = 0.0
      DO 30 J=N,1,-1
30      SUM = SUM + A(J)
      ERROR = TRUE - SUM  
C
      PRINT *, 'SMALLEST TO LARGEST SUM = ', SUM
      PRINT * ,'ERROR=', ERROR
      GO TO 10
      END


 HOW MANY TERMS(MAX=20000)?
 20000
 TRUE= 10.48072
 LARGEST TO SMALLEST SUM =  10.48075
 ERROR= -2.86102E-05
 SMALLEST TO LARGEST SUM =  10.48073
 ERROR= -5.72205E-06