def METHOD_NAME(self):
    '''
    smooth the rho
    '''
    mesh = self.mesh
    cell = mesh.entity('cell')
    isExtremeNode = self.is_extreme_node()
    node2cell = mesh.ds.node_to_cell()
    inva = 1/self.area
    s = node2cell@inva
    for i in range(2):
        crho = (self.rho[cell[:, 0]] + self.rho[cell[:, 1]] + self.rho[cell[:, 2]])/3.0
        rho = np.asarray(node2cell@(crho*inva))/s
        self.rho[~isExtremeNode] = rho[~isExtremeNode]