一个凹函数的图象总在它的切线的下方。

The graph of a concave function is always below its tangent.

youdao

图4：格拉齐亚诺说，大自然讲一种语言，有时这语言非常复杂——象这个函数，其图形与这个沙堆的形状相吻合。

Nature speaks a language, Graziano says, and sometimes that language can look pretty complicated—like the function whose graph mirrors the shape of this pile of sand. (March 2009.)

youdao

正如前面章节从图象到高度图所提到的，地形库有一个函数使用三角形带来创建一个显示列表。

As mentioned in section Height Maps from Images, the terrain lib has a function to create a display list using triangle strips.

youdao