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    "决策树的决策边界有一个很明显的特点：**轴平行**（axis-parallel），也就是说它的分类边界由若干个与坐标轴平行的分段组成，比如下图中的决策树和相应的决策边界：\n",
    "\n",
    "<img src=\"../images/decision-tree-axis-parallel.png\" width=\"400px\" />\n",
    "\n",
    "如果决策边界不是轴平行的，而是使用斜的划分边界，不仅模型会简单得多，而且泛化性能也能得到提高。\n",
    "\n",
    "<img src=\"../images/decision-tree-multi-variate.png\" width=\"400px\" />"
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