docs: def add_homogeneous_model(self, magnitude, phase=0, frequency=None):
          """Add homogeneous models to one or all tomodirs. Register those as
          forward models
  
          Parameters
          ----------
          magnitude : float
              Value of homogeneous magnitude model
          phase : float, optional
              Value of homogeneous phase model. Default 0
          frequency : float, optional
              Frequency of of the tomodir to use. If None, then apply to all
              tomodirs. Default is None.
          """
          if frequency is None:
              frequencies = self.frequencies
          else:
              assert isinstance(frequency, Number)
              frequencies = [frequency, ]
  
          for freq in frequencies:
              pidm, pidp = self.tds[freq].add_homogeneous_model(magnitude, phase)
              self.a['forward_rmag'][freq] = pidm
              self.a['forward_rpha'][freq] = pidp