[SRILM User List] big difference between ppl and ppl1

[Saman Noorzadeh]

I  made 2 models of 2 languages, Dutch and English, to make a language recognition.
I got the following perplexities:

Model: Dutch    Test: English    ppl:55    ppl2: 2* 10^18
Model: Dutch    Test: Dutch   ppl:303   ppl2: 400
Model: English   Test: Dutch   ppl: 600  ppl2: 3122ses n

Model: English  Test: English    ppl: 227   ppl2: 1897

I think it is reasonable if I have a large perplexity when my model and test are different but why ppl=55 when having a Duch model and an English test?
and

Why is there a BIG difference in their ppl and ppl1 ?

Thanks in advance
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