Could u explain how to define the perplexity?

[xuanzhaopeng]

I found if If I define the perplexity small than 0, then the K always be 0, because you define
int K = (float)perplexity * 3, so K always be 0.

If I define the perplexity > 0, then I will get segmentation fault.....(because the sizeof (distances) != K)

I'd like to know, this source code still could be use? or you already don't use it any more ....

[lvdmaaten]

How should I set the perplexity in t-SNE?

The performance of t-SNE is fairly robust under different settings of the perplexity. The most appropriate value depends on the density of your data. Loosely speaking, one could say that a larger / denser dataset requires a larger perplexity. Typical values for the perplexity range between 5 and 50.

What is perplexity anyway?

Perplexity is a measure for information that is defined as 2 to the power of the Shannon entropy. The perplexity of a fair die with k sides is equal to k. In t-SNE, the perplexity may be viewed as a knob that sets the number of effective nearest neighbors. It is comparable with the number of nearest neighbors k that is employed in many manifold learners.