anchor.diff:         select case(trim(arg))
          case('-h','--help')
             ! print help and exit
  -          write(0,*) trim(syntax)
  +          write(0,100)
             error_code = 1
             return
          case('-p','--prm')
  
positive.code: 
      if (nargs == 0) then
         ! no args: print syntax and stop
         write(0,*) trim(syntax)
         error_code = 1
         return
      end if
  
negative.code:        end if
      end if
  
  100 format(&
           'elss-sample (elss v0.2.1)                                                      '/& 
           '                                                                               '/&
           'Usage:                                                                         '/&
           '    elss-sample [options] -p <parameters_file>                                 '/&
           '    elss-learn [options] -c <checkpoint_file>                                  '/&
           '                                                                               '/&
           'Description:                                                                   '/&
           '    Simulate a trajectory in sequence space, using a model of pairwise         '/&
           '    interacting variables. The parameters of the model can either be read from '/&
           '    a file of parameters or from a checkpoint file generated by elss-learn.    '/&
           '                                                                               '/&
           'Required:                                                                      '/&
           '-p, --prm <prm_file>                                                           '/&
           '    Read the parameters of the model from file <prm_file>.                     '/&
           '                                                                               '/&
           '-c, --chk <chk_file>                                                           '/&
           '    Read the parameters of the model and the starting point for the simulation '/&
           '    from checkpoint file <chk_file>.                                           '/&
           '                                                                               '/&
           'Options:                                                                       '/&
           '-h, --help                                                                     '/&
           '    Display this help and exit.                                                '/&
           '                                                                               '/&
           '--prefix <str>                                                                 '/&         
           '    Prefix of output files.                                                    '/&
           '                                                                               '/&
           '-n, --nsweeps <n>, integer                                                     '/&
           '    Simulate <n> MC sweeps.                                                    '/&
           '    [default: 1000]                                                            '/&
           '                                                                               '/&
           '-u, --nupdate <n>, integer                                                     '/&
           '    Update model averages every <n> sweeps.                                    '/&
           '    [default: 10]                                                              '/&
           '                                                                               '/&
           '--seed <seed>, integer                                                         '/&
           '    Seed for initialization of pseudo-random number generator.                 '/&
           '    If == 0, the seed is computed from the system clock.                       '/&
           '    [default: 0]                                                               '/&
           '                                                                               '/&
           '-s, --seq <file>, string                                                       '/&
           '    Read the starting sequence from file <file>.                               '/&
           '    Overrides the starting sequence read in checkpoint file.                   '/&
           '    [default: generate random starting sequence]                               '/&
           '                                                                               '/&
           'Examples:                                                                      '/&
           '                                                                               '/)
  
    end subroutine command_line_read
  
  end module sample_command_line
  