It shows the standard deviation of the return on the portfolio as a function of the expected return on the portfolio.

它是投资组合的收益标准差,关于预期收益率的函数图像。

耶鲁公开课 - 金融市场课程节选

The standard library, that first line of code, it's not strictly necessary but any time you use a function, a tool that someone else wrote that lives in that so called library, you do need that include line as we'll see.

标准库函数--第一行代码，严格来说，不是每次都要写的，但是一旦你调用某个别人写，的函数，而这个函数又恰巧位于标准库里面,你就要像我们看到的这样，把它include进去。

哈佛公开课 - 计算机科学课程节选