如何建立一个超图详解

1.图和超图

图作为一种数据结构,由节点和边组成,可由下图表示。其中一个边只能链接两个节点。一个图可表示为G=(v,e,w)

其中v表示节点,e表示边,w表示节点的特征。关于图的表示可参考,本文不再详述。

在这里插入图片描述

对于超图,其与图结构最主要的区别就是一条边可以连接多个节点,因此我们可以认为图是一种特殊的超图。超图结构如下图所示。

在这里插入图片描述

在这里插入图片描述

超图可表示为G=(υ,ε,ω)。其中υ为节点集合,ε为超边集合,ω为超边权重的对称矩阵。超图G可以关联矩阵H来表示,其词条定义为:

在这里插入图片描述

改公式可解释为如果某个节点属于某个超边,则关联矩阵H的值为1,否则为0。

对于单个节点v可定义为:

在这里插入图片描述

可解释为连接该节点的所有边乘上权重向量的和。

Dₑ和Dᵥ由d(v)和s(e)分别表示为超边和节点的对角矩阵。

单个边可定义为:

在这里插入图片描述

可以理解为该边包含的所有节点之和。

2.实例

下面举出一个具体实例帮助理解超图的构建。以该图为例

在这里插入图片描述

图中有8个节点,3个超边。超边的细化图如下:

在这里插入图片描述

假设权重&W&为全1矩阵,因为它对构建超图数据结果无影响,那么H为一个3行8列的矩阵,表示为:

h(1,1) = 0

h(2,1) = 1

h(3,1) = 0

h(4,1) = 1

h(5,1) = 0

h(6,1) = 0

h(7,1) = 0

h(8,1) = 1

h(1,2) = 1

h(2,2) = 0

h(3,2) = 0

h(4,2) = 0

h(5,2) = 0

h(6,2) = 1

h(7,2) = 1

h(8,2) = 0

h(1,3) = 0

h(2,3) = 0

h(3,3) = 1

h(4,3) = 0

h(5,3) = 1

h(6,3) = 0

h(7,3) = 1

h(8,3) = 0

H =

De​表示为:

d(1) = 1

d(2) = 1

d(3) = 1

d(4) = 1

d(5) = 1

d(6) = 1

d(7) = 2

d(8) = 1

Dv​表示为:

s(1) = 3

s(2) = 3

s(3) = 3

3.代码实现

下面我们用python代码进行编程,我们的目标是在知道节点的特征W通过特征的距离来生成 G /mathcal{G} G矩阵。路线为:W,H, G /mathcal{G} G。主要代码如下:

import numpy as np#KNN生成Hx = np.array([[1,0,0,0,1,0,1,0,0,0],        [1,1,1,0,0,0,1,1,1,0],       [1,1,1,0,0,1,1,1,1,0],       [0,1,0,0,0,0,1,0,1,0],       [1,1,1,1,0,0,1,1,0,1],       [1,0,1,0,0,1,0,1,1,0],       [0,1,0,0,1,0,1,1,1,0],       [0,1,1,0,1,0,1,0,1,1]])def Eu_dis(x):    """    Calculate the distance among each raw of x    :param x: N X D                N: the object number                D: Dimension of the feature    :return: N X N distance matrix    """    x = np.mat(x)    aa = np.sum(np.multiply(x, x), 1)    ab = x * x.T    dist_mat = aa + aa.T - 2 * ab    dist_mat[dist_mat < 0] = 0    dist_mat = np.sqrt(dist_mat)    dist_mat = np.maximum(dist_mat, dist_mat.T)    return dist_matdef hyperedge_concat(*H_list):    """    Concatenate hyperedge group in H_list    :param H_list: Hyperedge groups which contain two or more hypergraph incidence matrix    :return: Fused hypergraph incidence matrix    """    H = None    for h in H_list:        if h is not None and h != []:            # for the first H appended to fused hypergraph incidence matrix            if H is None:                H = h            else:                if type(h) != list:                    H = np.hstack((H, h))                else:                    tmp = []                    for a, b in zip(H, h):                        tmp.append(np.hstack((a, b)))                    H = tmp    return Hdef construct_H_with_KNN_from_distance(dis_mat, k_neig, is_probH=True, m_prob=1):    """    construct hypregraph incidence matrix from hypergraph node distance matrix    :param dis_mat: node distance matrix    :param k_neig: K nearest neighbor    :param is_probH: prob Vertex-Edge matrix or binary    :param m_prob: prob    :return: N_object X N_hyperedge    """    n_obj = dis_mat.shape[0]    # construct hyperedge from the central feature space of each node    n_edge = n_obj    H = np.zeros((n_obj, n_edge))    for center_idx in range(n_obj):        dis_mat[center_idx, center_idx] = 0        dis_vec = dis_mat[center_idx]        nearest_idx = np.array(np.argsort(dis_vec)).squeeze()        avg_dis = np.average(dis_vec)        if not np.any(nearest_idx[:k_neig] == center_idx):            nearest_idx[k_neig - 1] = center_idx        for node_idx in nearest_idx[:k_neig]:            if is_probH:                H[node_idx, center_idx] = np.exp(-dis_vec[0, node_idx] ** 2 / (m_prob * avg_dis) ** 2)            else:                H[node_idx, center_idx] = 1.0    return Hdef construct_H_with_KNN(X, K_neigs=[10], split_diff_scale=False, is_probH=True, m_prob=1):    """    init multi-scale hypergraph Vertex-Edge matrix from original node feature matrix    :param X: N_object x feature_number    :param K_neigs: the number of neighbor expansion    :param split_diff_scale: whether split hyperedge group at different neighbor scale    :param is_probH: prob Vertex-Edge matrix or binary    :param m_prob: prob    :return: N_object x N_hyperedge    """    if len(X.shape) != 2:        X = X.reshape(-1, X.shape[-1])    if type(K_neigs) == int:        K_neigs = [K_neigs]    dis_mat = Eu_dis(X)    H = []    for k_neig in K_neigs:        H_tmp = construct_H_with_KNN_from_distance(dis_mat, k_neig, is_probH, m_prob)        if not split_diff_scale:            H = hyperedge_concat(H, H_tmp)        else:            H.append(H_tmp)    return HH = construct_H_with_KNN(x)#生成Gdef generate_G_from_H(H, variable_weight=False):    """    calculate G from hypgraph incidence matrix H    :param H: hypergraph incidence matrix H    :param variable_weight: whether the weight of hyperedge is variable    :return: G    """    if type(H) != list:        return _generate_G_from_H(H, variable_weight)    else:        G = []        for sub_H in H:            G.append(generate_G_from_H(sub_H, variable_weight))        return Gdef _generate_G_from_H(H, variable_weight=False):    """    calculate G from hypgraph incidence matrix H    :param H: hypergraph incidence matrix H    :param variable_weight: whether the weight of hyperedge is variable    :return: G    """    H = np.array(H)    n_edge = H.shape[1]    # the weight of the hyperedge    W = np.ones(n_edge)    # the degree of the node    DV = np.sum(H * W, axis=1)    # the degree of the hyperedge    DE = np.sum(H, axis=0)    invDE = np.mat(np.diag(np.power(DE, -1)))    DV2 = np.mat(np.diag(np.power(DV, -0.5)))    W = np.mat(np.diag(W))    H = np.mat(H)    HT = H.T    if variable_weight:        DV2_H = DV2 * H        invDE_HT_DV2 = invDE * HT * DV2        return DV2_H, W, invDE_HT_DV2    else:        G = DV2 * H * W * invDE * HT * DV2        return GG = generate_G_from_H(H)

实验结果:

H

在这里插入图片描述

G

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