Python 实现pagerank

pagerank的源代码如下：

#coding=utf-8

S=[[0.25,0,0,0],[0.25,0,0,1],[0.25,0.5,0,0],[0.25,0.5,1,0]] #转移矩阵
M=[0.25,0.25,0.25,0.25]  #初始矩阵
alpha=0.85  # 阻尼系数


def vmat(mat, vector):
    if len(mat[0]) != len(vector):
        print "can’t cacl mat*vector !"
        return
    res = [0.0 for i in range(len(mat))]
    for i in range(0, len(mat)):
        for j in range(0, len(mat[1])):
            res[i] += float(mat[i][j] * vector[j])
    return res


def avector(a, vector):
    res = [0.0  for i in range(len(vector))]
    for i in range(len(vector)):
        res[i] = float(vector[i] * a)
    return res


def addvector(vector1, vector2):
    if len(vector1) != len(vector2):
        print "can’t add vector !"
        return
    res = [0.0 for i in range(len(vector1))]
    for i in range(len(vector1)):
        res[i] = float(vector1[i] + vector2[i])
    return res


def pagerank(S, M, alpha):
    v = vmat(S, M)
    av = avector(alpha, v)
    random = avector(1 - alpha, M)
    add = addvector(av, random)
    return add


if __name__ == '__main__':
    add = pagerank(S, M, alpha)
    new_add = add
    flag = True
    while(flag):
        flag = False
        new_add = pagerank(S, add, alpha)
        print new_add
        for i in range(len(add)):
            if round(new_add[i], 5) != round(add[i], 5):
                flag = True
        add = new_add

    print new_add

最终结果如下：