docs: def _compute_cell_circumcenters(self):
          """Computes the center of the circumsphere of each cell.
          """
          # Just like for triangular cells, tetrahedron circumcenters are most easily
          # computed with the quadrilateral coordinates available.
          # Luckily, we have the circumcenter-face distances (cfd):
          #
          #   CC = (
          #       + cfd[0] * face_area[0] / sum(cfd*face_area) * X[0]
          #       + cfd[1] * face_area[1] / sum(cfd*face_area) * X[1]
          #       + cfd[2] * face_area[2] / sum(cfd*face_area) * X[2]
          #       + cfd[3] * face_area[3] / sum(cfd*face_area) * X[3]
          #       )
          #
          # (Compare with
          # <https://en.wikipedia.org/wiki/Trilinear_coordinates#Between_Cartesian_and_trilinear_coordinates>.)
          # Because of
          #
          #    cfd = zeta / (24.0 * face_areas) / self.cell_volumes[None]
          #
          # we have
          #
          #   CC = sum_k (zeta[k] / sum(zeta) * X[k]).
          #
          alpha = self._zeta / numpy.sum(self._zeta, axis=0)
  
          self._circumcenters = numpy.sum(
              alpha[None].T * self.node_coords[self.cells["nodes"]], axis=1
          )
          return