Qs about the LDA calculate Perplexity

[Bocong Liu]

Hi,

In CVB0Driver.java, I notice the change rate of perplexity is
calculated as follows:


  private static double rateOfChange(List<Double> perplexities) {

...
    return Math.abs(perplexities.get(sz - 1) - perplexities.get(sz -
2)) / perplexities.get(0);

  }

Why do we always use the first perplexity as the denominator?
shouldn't it be better if we use perplexities.get(sz - 2), which will
make us easier to choose the value of convergence delta.

Thanks,
Bocong Liu