训练n-gram语言模型
ngram-count -text train.txt -order -lm model -kndiscount -interpolate -gt3min -gt4min
计算生成PPL
ngram -lm model -order -ppl test.txt -debug 2> srilm.ppl
ppl与ppl1有和区别？
ppl = 10^(-logprob / (words - OOVs + sentences))
ppl1 = 10^(-logprob / (words - OOVs))
ref:
http://www.speech.sri.com/projects/srilm/manpages/srilm-faq.7.html