anchor.diff:            write(error_string,*) trim(data_file)
             return
          end if
  -
  +       
          ! open data file
          call units_open(data_file,'old',udata,err)
          if( err /= 0 ) then
  
positive.code:           write(error_string,*) trim(data_file)
            return
         end if
  
      end if
  
    end subroutine command_line_read
  
negative.code:        end if
      end if
  
      mode = 'LEARN'
      
      if ( mc_nsweeps <= 0 ) then
         error_code = 10
         write(error_string,*) mc_nsweeps
         return
      end if
      
      if ( ww_file /= "" ) then
         inquire( file = ww_file, exist = file_exists )
         if ( .not. file_exists ) then
            error_code = 8
            write(error_string,*) trim(ww_file)
            return
         end if
         call units_open(ww_file,'old',uwgt,err)
         if( err /= 0 ) then
            error_code = 19
            write(error_string,*) trim(ww_file)
            return
         end if
      end if
      
      if ( uwgt > 0 .and. wid >= 0.0_kflt ) then
         error_code = 14
         return
      end if
  
      if( data_file == '' ) then
  
         error_code = 3
         return
  
      else
  
  