Hi,

I am trying to train phrase models for several language pairs. Before training 
the phrase models, I cleaned the corpora with the moses clean script, so 
sentences with a length >60 were filtered out. This worked for several corpora. 
For a few corpora, I got "WARNING: Model2 viterbi alignment has zero score." I 
found that another person solved the problem by reducing the length of the 
sentences, so I reduced the length of the sentences to 50 for these corpora. 
This worked for the problematic corpora except for one corpora pair. For this 
corpora pair, I had to reduce the length of the sentences to 30, so that it 
finally worked. By reducing the length to 30, I'm loosing a high number of 
sentences of my corpora. That's why I was wondering which is the reason for 
this warning and why for some language pairs it works with longer sentences and 
for others it doesn't.I also checked the ratio of 9:1. Can you imagine any 
reason for this warning? And, since it is marked as a warning, not as an error, 
is it necessary to remove it?It would be very kind if you could give me some 
information about this problem.
Thank you,Patricia

Extract from the logfile:
   406  THTo3: Iteration 1   407  Reading more sentence pairs into memory ...   
408  WARNING: Model2 viterbi alignment has zero score.   409  Here are the 
different elements that made this alignment probability zero   410  Source 
length 4 target length 35   411  best: fs[1] 1  : es[3] 3 ,  a: 0.13803 t: 
0.870283 score 0.120125  product : 0.120125 ss 0   412  best: fs[2] 2  : es[1] 
1 ,  a: 0.350718 t: 0.221544 score 0.0776995  product : 0.00933363 ss 0   413  
best: fs[3] 3  : es[1] 1 ,  a: 0.150805 t: 0.324392 score 0.0489198  product : 
0.000456599 ss 0   414  best: fs[4] 4  : es[1] 1 ,  a: 0.0606276 t: 0.324392 
score 0.0196671  product : 8.97998e-06 ss 0   415  best: fs[5] 5  : es[1] 1 ,  
a: 0.037479 t: 0.324392 score 0.0121579  product : 1.09178e-07 ss 0   416  
best: fs[6] 6  : es[1] 1 ,  a: 0.021535 t: 0.324392 score 0.0069858  product : 
7.62692e-10 ss 0   417  best: fs[7] 7  : es[1] 1 ,  a: 0.041835 t: 0.324392 
score 0.0135709  product : 1.03505e-11 ss 0   418  best: fs[8] 8  : es[1] 1 ,  
a: 0.12501 t: 0.324392 score 0.0405522  product : 4.19734e-13 ss 0   419  best: 
fs[9] 9  : es[1] 1 ,  a: 0.333332 t: 0.324392 score 0.10813  product : 
4.5386e-14 ss 0   420  best: fs[10] 10  : es[1] 1 ,  a: 0.999996 t: 0.324392 
score 0.324391  product : 1.47228e-14 ss 0   421  best: fs[11] 11  : es[1] 1 ,  
a: 0.999996 t: 0.324392 score 0.324391  product : 4.77594e-15 ss 0   422  best: 
fs[12] 12  : es[1] 1 ,  a: 0.999996 t: 0.324392 score 0.324391  product : 
1.54927e-15 ss 0   423  best: fs[13] 13  : es[1] 1 ,  a: 0.999996 t: 0.324392 
score 0.324391  product : 5.0257e-16 ss 0   424  best: fs[14] 14  : es[1] 1 ,  
a: 0.999996 t: 0.324392 score 0.324391  product : 1.63029e-16 ss 0   425  best: 
fs[15] 15  : es[1] 1 ,  a: 0.999996 t: 0.324392 score 0.324391  product : 
5.28852e-17 ss 0   426  best: fs[16] 16  : es[1] 1 ,  a: 0.999996 t: 0.324392 
score 0.324391  product : 1.71555e-17 ss 0   427  best: fs[17] 17  : es[1] 1 ,  
a: 0.999996 t: 0.324392 score 0.324391  product : 5.56508e-18 ss 0   428  best: 
fs[18] 18  : es[1] 1 ,  a: 0.999996 t: 0.324392 score 0.324391  product : 
1.80526e-18 ss 0   429  best: fs[19] 19  : es[1] 1 ,  a: 0.999996 t: 0.324392 
score 0.324391  product : 5.85611e-19 ss 0   430  best: fs[20] 20  : es[1] 1 ,  
a: 0.999996 t: 0.324392 score 0.324391  product : 1.89967e-19 ss 0   431  best: 
fs[21] 21  : es[1] 1 ,  a: 0.999996 t: 0.324392 score 0.324391  product : 
6.16235e-20 ss 0   432  best: fs[22] 22  : es[1] 1 ,  a: 0.999996 t: 0.324392 
score 0.324391  product : 1.99901e-20 ss 0   433  best: fs[23] 23  : es[1] 1 ,  
a: 0.999996 t: 0.324392 score 0.324391  product : 6.48461e-21 ss 0   434  best: 
fs[24] 24  : es[1] 1 ,  a: 0.999996 t: 0.324392 score 0.324391  product : 
2.10355e-21 ss 0   435  best: fs[25] 25  : es[1] 1 ,  a: 0.999996 t: 0.324392 
score 0.324391  product : 6.82372e-22 ss 0   436  best: fs[26] 26  : es[1] 1 ,  
a: 0.999996 t: 0.324392 score 0.324391  product : 2.21355e-22 ss 0   437  best: 
fs[27] 27  : es[1] 1 ,  a: 0.999996 t: 0.324392 score 0.324391  product : 
7.18057e-23 ss 0   438  best: fs[28] 28  : es[1] 1 ,  a: 0.999996 t: 0.324392 
score 0.324391  product : 2.32931e-23 ss 0   439  best: fs[29] 29  : es[1] 1 ,  
a: 0.999996 t: 0.324392 score 0.324391  product : 7.55608e-24 ss 0   440  best: 
fs[30] 30  : es[1] 1 ,  a: 0.999996 t: 0.324392 score 0.324391  product : 
2.45112e-24 ss 0   441  best: fs[31] 31  : es[1] 1 ,  a: 0.999996 t: 0.324392 
score 0.324391  product : 7.95122e-25 ss 0   442  best: fs[32] 32  : es[1] 1 ,  
a: 0.999996 t: 0.324392 score 0.324391  product : 2.5793e-25 ss 0   443  best: 
fs[33] 33  : es[1] 1 ,  a: 0.999996 t: 0.324392 score 0.324391  product : 
8.36703e-26 ss 0   444  best: fs[34] 34  : es[1] 1 ,  a: 0.999996 t: 0.324392 
score 0.324391  product : 2.71419e-26 ss 0   445  best: fs[35] 35  : es[1] 1 ,  
a: 0.99992 t: 0.0101365 score 0.0101357  product : 2.75101e-28 ss 0   446  
Fert[0] selected 9   447  Fert[1] selected 9   448  Fert[2] selected 0   449  
Fert[3] selected 9   450  Fert[4] selected 8   451  10000   452  20000   453  
30000   454  40000   455  50000   456  Reading more sentence pairs into memory 
...   457  Reading more sentence pairs into memory ...   458  
#centers(pre/hillclimbed/real): 1 1 1  #al: 1075.58 
#alsophisticatedcountcollection: 0 #hcsteps: 0   459  #peggingImprovements: 0   
460  A/D table contains 104118 parameters.   461  A/D table contains 104094 
parameters.   462  NTable contains 397690 parameter.   463  p0_count is 
1.09339e+06 and p1 is 113340; p0 is 0.999 p1: 0.001   464  THTo3: TRAIN 
CROSS-ENTROPY 4.26144 PERPLEXITY 19.1788   465  THTo3: (1) TRAIN VITERBI 
CROSS-ENTROPY 4.34002 PERPLEXITY 20.2523   466   467  THTo3 Viterbi Iteration : 
1 took: 44 seconds

                                                                                
  
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