write_vector_plot Subroutine

subroutine write_vector_plot ( command_file_name, data_file_name, &
  ierror )
!
!*******************************************************************************
!
!! WRITE_VECTOR_PLOT writes GNUPLOT commands to plot vectors.
!
!
!  Modified:
!
!    22 February 2001
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, character ( len = * ) COMMAND_FILE_NAME, the name of the
!    command file.
!
!    Input, character ( len = * ) DATA_FILE_NAME, the name of the data file.
!
!    Output, integer IERROR, nonzero if an error occurred.
!
  implicit none
!
  character ( len = * ) command_file_name
  character ( len = * ) data_file_name
  integer file_unit
  integer ierror
  integer ios
!
!  Write the data file.
!
  ierror = 0

  call get_unit ( file_unit )

  if ( file_unit == 0 ) then
    ierror = 1
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) 'WRITE_VECTOR_PLOT - Fatal error!'
    write ( *, '(a)' ) '  Could not get a free FORTRAN unit.'
    return
  end if

  open ( unit = file_unit, file = command_file_name, status = 'replace', &
    iostat = ios )

  if ( ios /= 0 ) then
    ierror = 2
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) 'WRITE_VECTOR_PLOT - Fatal error!'
    write ( *, '(a)' ) '  Could not open the output file.'
    return
  end if

  write ( file_unit, '(a)' ) 'set title "GNUFOR plot"'
  write ( file_unit, '(a)' ) 'set xlabel "x"'
  write ( file_unit, '(a)' ) 'set ylabel "y"'
  write ( file_unit, '(a)' ) 'set style arrow'
  write ( file_unit, '(a,i2,a)' ) 'plot "' // trim ( data_file_name )
  write ( file_unit, '(a)' ) 'pause -1  "Hit return to continue"'
  write ( file_unit, '(a)' ) 'q'

  close ( unit = file_unit )

  write ( *, '(a)' ) ' '
  write ( *, '(a)' ) 'WRITE_VECTOR_PLOT:'
  write ( *, '(a)' ) '  Wrote the GNUPLOT table plots command file "' // &
    trim ( command_file_name ) // '"'

  return
endsubroutine write_vector_plot