code: def beta_r(self, r, kwargs):
          
          if self._type == 'const':
              return self.const_beta(kwargs)
          elif self._type == 'OsipkovMerritt':
              return self.ospikov_meritt(r, kwargs)
          elif self._type == 'Colin':
              return self.colin(r, kwargs)
          elif self._type == 'isotropic':
              return self.isotropic()
          elif self._type == 'radial':
              return self.radial()
          else:
              raise ValueError('anisotropy type %s not supported!' % self._type)
docs: returns the anisotorpy parameter at a given radius
          :param r:
          :return: