docs: def cmd():
      """Implementation of field subcommand.
  
      Other Parameters:
          conf.field
          conf.core
      """
      sdat = StagyyData(conf.core.path)
      sovs = set_of_vars(conf.field.plot)
      minmax = {}
      if conf.plot.cminmax:
          conf.plot.vmin = None
          conf.plot.vmax = None
          for step in sdat.walk.filter(snap=True):
              for var, _ in sovs:
                  if var in step.fields:
                      if var in phyvars.FIELD:
                          dim = phyvars.FIELD[var].dim
                      else:
                          dim = phyvars.FIELD_EXTRA[var].dim
                      field, _ = sdat.scale(step.fields[var], dim)
                      if var in minmax:
                          minmax[var] = (min(minmax[var][0], np.nanmin(field)),
                                         max(minmax[var][1], np.nanmax(field)))
                      else:
                          minmax[var] = np.nanmin(field), np.nanmax(field)
      for step in sdat.walk.filter(snap=True):
          for var in sovs:
              if var[0] not in step.fields:
                  print("'{}' field on snap {} not found".format(var[0],
                                                                 step.isnap))
                  continue
              opts = {}
              if var[0] in minmax:
                  opts = dict(vmin=minmax[var[0]][0], vmax=minmax[var[0]][1])
              fig, axis, _, _ = plot_scalar(step, var[0], **opts)
              if valid_field_var(var[1]):
                  plot_iso(axis, step, var[1])
              elif var[1]:
                  plot_vec(axis, step, var[1])
              oname = '{}_{}'.format(*var) if var[1] else var[0]
              misc.saveplot(fig, oname, step.isnap)