docs: def SQRT(argument):
      """ Computes the square matrix of the argument
  
      :param argument: a dataset region field (dataset.field) or metadata (dataset['field'])
      """
      if isinstance(argument, MetaField):
          return argument._unary_expression("SQRT")
      elif isinstance(argument, RegField):
          return argument._unary_expression("SQRT")
      else:
          raise TypeError("You have to give as input a RegField (dataset.field)"
                          "or a MetaField (dataset['field']")