This is a density function which peaks sharply in the centre and falls off smoothly to zero at the boundaries. It’s defined as:
Negative net migration hasn’t definitively happened in the U.S. for almost a century, not since the Great Depression. The U.S. native-born population is also in free fall, well below the replacement rate needed to maintain population numbers in the long run. With fewer immigrant arrivals already dealing a blow to the workforce, the shrinkage of the American taxpayer base is set to further widen the country’s deficit and hurt its prospects for economic growth.
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去了美国之后，有一次看到PBS公共电视某个节目在介绍《了不起的盖茨比》，这是我当年看到的同一本书吗？怎么感觉完全不一样呢？根据那个节目的介绍，那应该是一本非常哀伤而又有诗意的小说，我怎么记得那本书是非常夸张滑稽的呢？赶快去把原文找来看，确实是非常哀伤的一本作品。《大亨小传》这个书名我们已耳熟能详，沿用至今，却与作者菲茨杰拉德的原意相去甚远。