docs: def _write_crmod_file(filename):
      """Write a valid crmod configuration file to filename.
  
      TODO: Modify configuration according to, e.g., 2D
      """
      crmod_lines = [
          '***FILES***',
          '../grid/elem.dat',
          '../grid/elec.dat',
          '../rho/rho.dat',
          '../config/config.dat',
          'F                ! potentials ?',
          '../mod/pot/pot.dat',
          'T                ! measurements ?',
          '../mod/volt.dat',
          'F               ! sensitivities ?',
          '../mod/sens/sens.dat',
          'F                ! another dataset ?',
          '1                ! 2D (=0) or 2.5D (=1)',
          'F                ! fictitious sink ?',
          '1660             ! fictitious sink node number',
          'F                ! boundary values ?',
          'boundary.dat',
      ]
  
      with open(filename, 'w') as fid:
          [fid.write(line + '\n') for line in crmod_lines]