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    "层次聚类分为 **聚合**（agglomerative）和 **分裂**（divisive）两种方法，也称为 **自下而上**（bottom-up）和 **自上而下**（top-down）。聚合聚类开始将每个样本各自分到一个类，之后将相距最近的两个类合并，建立一个新类，重复此操作直到满足停止条件。而分裂聚类相反，开始将所有样本分到一个类，之后将已有类中相距最远的样本分到两个新类，重复此操作直到满足停止条件。\n",
    "\n",
    "层次聚类需要明确下面三个要素：\n",
    "\n",
    "* 距离或相似度算法：闵氏距离、马氏距离、相关系数、夹角余弦等\n",
    "* 合并规则：一般通过类间距离最小来进行合并，类间距离可以是最短距离、最长距离、中心距离、平均距离等\n",
    "* 停止条件：类的个数达到某个阈值，类的直径超过某个阈值等\n",
    "\n",
    "### **AGNES算法**（AGglomerative NESting）\n",
    "\n",
    "AGNES算法是经典的自下而上聚类算法。\n",
    "\n",
    "### **DIANA算法**（DIvisive ANAlysis）\n",
    "\n",
    "DIANA算法是经典的自上而下聚类算法。"
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