逻辑回归本来是做二分类的，可以做二分类的也可以做多分类，以下的数据demo，就做了多分类！
股票的涨跌，房价的涨跌等等都是二分类的问题！
multi-class classification 多分类分类器
:Summary Statistics:
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Min Max Mean SD Class Correlation
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sepal length: 4.3 7.9 5.84 0.83 0.7826 萼片(sepal)
sepal width: 2.0 4.4 3.05 0.43 -0.4194
petal length: 1.0 6.9 3.76 1.76 0.9490 (high!) 花瓣(petal)
petal width: 0.1 2.5 1.20 0.76 0.9565 (high!)
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a binary problem 二元问题，或翻译成二分类问题。