PROGRAM vecgen
!
!  This program randomly generates an N-length vector and writes it to
!  a file, with N on the first line, and the rest of the array on
!  following line(s).
!
   IMPLICIT NONE
   INTEGER N
   DOUBLE PRECISION, ALLOCATABLE :: V(:)

   PRINT *, 'Enter N (> 0)'
   READ *, N
   IF (N .lt. 1) THEN
      PRINT*, 'N must be greater than 0, but you used:', N
      STOP
   END IF
   ALLOCATE(V(N))               ! allocate array
   CALL RANDOM_NUMBER(V)        ! randomly generate array
!
!  Write array to file, and quit
!
   OPEN(unit=10, file='vector.dat', status='replace', action='write')
   WRITE(10, *) N
   WRITE(10, *) V
   CLOSE(10)
   DEALLOCATE(V)
   PRINT *, 'Results written to file ''vector.dat'''

END PROGRAM vecgen