困惑度(Perplexity, PPL)是一种用来评价语言模型好坏的指标。 直观上理解，当我们给定一段非常标准的，高质量的，符合人类自然语言习惯的文档作为测试集时，模型生成这段文本的概率越高，就认为模型的困惑度越小，模型也就越好。

2024年4月1日 · PyTorch PPL（Perplexity，困惑度）是用于评估语言模型性能的指标。它是交叉熵损失的指数函数。在PyTorch中，可以使用`F.cross_entropy`函数来计算交叉熵损失，然后使用`torch.exp`函数对损失进行指数化得到PPL。

Perplexity仅仅是entropy的一个指数化形式： PPL (P, Q) = 2^ {H (P, Q)}。 若是要给予它一个含义，直观上，Perplexity可以理解为对预测序列不确定性的衡量。 语言模型的Perplexity可以看成是预测后面tokens时的不确定程度。 考虑一个具有三位entropy的语言模型，其中每一位都编码两个等概率的可能结果。 这意味着在预测下一个token时，该语言模型必须在 2^3 = 8 个可能的选项中进行选择。 因此，我们可以认为该语言模型的Perplexity为 8。

实际上，PPL就是用交叉熵loss来计算的【公式7】。loss越小，模型越好，这点很容易理解，而这个时候，跟loss有单调关系的PPL也会越小。交叉熵loss也反映了语言模型学到的分布与实际数据分布的差异，所以语言模型的分布与给定数据集越接近，PPL也就越小。

2018年12月21日 · Texas Motor Speedway claims to be able to hold 180,000 people, but that includes the skybox seats high above too. If you're going to talk in front of an audience it's fun to visualize how big that audience size looks. Like what does it actually look like when there are 150 people in a room?

2011年4月4日 · Code reviewer wants us to revise our drawings and fixture count to reflect all parts of the building being fully occupied at all times. This calculation puts our occupant load ~3000 ppl and pretty much doubles the amount of fixtures and sizes of our restrooms.

This relationship, however, is sensitive to density itself, whereby increasing population density in compact developments initially results in diminishing emission reductions, and eventually "saturating" after density reaches 3,000 ppl/km 2. By contrast, dispersed developments show increasing returns to rising population density in the US West ...

2015年10月19日 · why are 3000 ppl playing and the server with max ppl i found have only 27 players , and the second most populated 7? have i done something wrong? i removed the ping limit and.. nothing.. all servers with 2 or 3 ppl unless that ones with 27 players , and 7.. can anyone say to me if this is normal please? sorry for my english and thanks hehe

2022年7月14日 · You need to visualize an even bigger theater for 1,000 people. And for a crowd of 3,000, they would barely fit most theaters, and some are going to have to stay outside. For a crowd of 10,000, imagine the audience in a game in a football stadium. But where can 20,000 people fit? Well, the O2 Arena in London can accommodate them well.

2024年7月15日 · World Population Prospects 2024 is the 28th edition of the official estimates and projections of the global population that have been published by the United Nations since 1951. The estimates are based on all available sources of data on population size and levels of fertility, mortality and international migration for 237 countries or areas.