This function always a returns a value, although it could be the value unknown.

该函数始终返回一个值，但是该值可能是unknown。

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Then, whenever we have a new data point, with an unknown output value, we put it through the model and produce our expected output.

之后，只要我们有一个输出值未知的新的数据点，我们都可以将其放入这个模型并生成预期的输出。

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The second was classification (also known as classification tree or decision tree), which can be used to create an actual branching tree to predict the output value of an unknown data point.

第二种技术是分类（即分类树或决策树），用来创建一个实际的分支树来预测某个未知数据点的输出值。

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Difficulties that everyday citizens (and voters) have with evaluating the merits of the most well-known financial services firms are multiplied when the challenge is to form a judgement on the long-term value provided by unknown, entrepreneurial firms who engage in financial transactions that are far removed from their own everyday lives.

FORBES: "Villains" of Financial Crisis Wrestle with Misperceptions

The value to mammoths of having two coat colours is unknown.

ECONOMIST: The genetics of mammoth coat colour

But if Apple cuts its profit margins to do it then jobs (some number, unknown) will disappear somewhere else as a result of the reduction in those profits and the value of Apple as a company.

FORBES: If Apple Onshored iPad Production it Would Create 67,000 American Manufacturing Jobs!