<hi xmlns="http://www.tei-c.org/ns/1.0" rend="bold" style="font-size:12pt">Topic coherence</hi> <hi xmlns="http://www.tei-c.org/ns/1.0" style="font-size:12pt">: Compared to the classification results, the evaluation from the perspective of topic coherence shows some differences between the two corpora. Firstly, it can be observed in Figure 3 that the maximum of the NPMI-score distributions decreases with the increase of Alpha from almost 0.3 to about 0.12. In addition, the median of the distributions also shows a decreasing trend. At Alpha = 0.01, the median is lower than the NPMI baseline if the number of topics is set higher than 100. However, at Alpha = 100, the median is already lower than the NPMI baseline if the number of topics is set to 70. Apart from that, we can observe that the topic models with a higher number of topics contain more topics with low NPMI scores, regardless of the setting of Alpha. Compared to the test on the newspaper corpus, the test results on the novel corpus are slightly different. When Alpha is set smaller than 1, the NPMI-score distributions do not show an evident change as Alpha increases, and the range of distribution is often broader when the number of topics is set between 60 and 300. Starting from Alpha being raised to greater than 1, the distributions of the NPMI-scores clearly change, and the results then are similar to the previous test on the newspaper corpus: the maximum of the NPMI-score distributions decreases with the increase of the Alpha, and topic models with a higher number of topics contain more topics with low NPMI scores.</hi>