code: def _get_cross_pt_dual_simp(self, dual_simp):
          
          matrix_surfs = [self.facets[dual_simp[i]].normal for i in range(3)]
          matrix_e = [self.facets[dual_simp[i]].e_surf for i in range(3)]
          cross_pt = sp.dot(sp.linalg.inv(matrix_surfs), matrix_e)
          return cross_pt
docs: |normal| = 1, e_surf is plane's distance to (0, 0, 0),
          plane function:
              normal[0]x + normal[1]y + normal[2]z = e_surf
  
          from self:
              normal_e_m to get the plane functions
              dual_simp: (i, j, k) simplices from the dual convex hull
                  i, j, k: plane index(same order in normal_e_m)