根据文档，我看不出这是为什么。

I don't see why this is a problem according to the documentation.

来自文档：

u和v之间的相关距离定义为 1-racfrac {（u-\bar {u}）\cdot（v-\bar {v}）}
{{||（u-\bar {u}）|| } _2 {||（v-\bar {v}）||} _2}

通过 Cauchy-Schwarz不等式，减号后的表达式带有绝对值为1 。但是，并没有规定它不会是负数的-实际上，如果（平均归一化的）向量是反相关的，就会发生这种情况。

By the Cauchy-Schwarz Inequality, the expression following the minus sign has an absolute value that is at most 1. There is nothing stipulating that it won't be negative, though - in fact, this will happen if the (mean normalized) vectors are anticorrelated.

AFAICT，您应该如果您得到的值大于2或小于0感到很惊讶。使用@Cleb的注释以及范围为[0，2]的事实，我猜想其他一些包将距离简单地定义为一半这个表达式。

AFAICT, you should be surprised if you'd get a value larger than 2 or smaller than 0. Using the comment by @Cleb and the fact that the range is [0, 2], I'm guessing that some other packages simply define the distance as half this expression.