使用基类对象指针或引用的函数必须能够在不了解衍生类的条件下使用衍生类的对象。

Functions that use Pointers or references to base classes must be able to use objects of derived classes without knowing it.

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衍生工具的存在并不总是假定和方法，制定了许多具体的情况。基本类的方法的基础上，光滑的目标函数，如下。

The existence of derivatives is not always assumed and many methods were devised for specific situations. The basic classes of methods, based on smoothness of the objective function, are.

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