/**
* @brief calculate interpolate weight
**/
public double get_lower_weight(NgramStat stat)
{
double total = stat.m_total;
double min1 = stat.m_min1;
double min2 = stat.m_min2;
double min3 = stat.m_min3;
return((m_d1 * (min1 - min2) + m_d2 * (min2 - min3) + m_d3plus * min3) / total);
}
/// <summary>
/// calculate the ngram prob and lower weight, and output them
/// @param context, n-gram prefix context
/// @param vec_ngram, all n-gram(of the same order) to calculate
/// @param stat, current n-gram occurrence statistics
/// @param discount, current n-gram discount constants
/// @param interpolate, whether to interpolate
/// </summary>
static void calc_ngram(string context, List <Ngram> vec_ngram, Discount discount,
bool interpolate, StreamWriter sw)
{
int order = context.Split().Length;
NgramStat cur_stat = new NgramStat();
cur_stat.reset();
//All ngrams with same context
for (int i = 0; i < vec_ngram.Count; i++)
{
Ngram ngram = vec_ngram[i];
if (ngram.word == null)
{
//This is unigram
if (ngram.occur >= g_min_count[0])
{
calc_unigram(context, ngram.occur, g_uni_stat, g_discounts[0], sw);
}
}
else
{
cur_stat.count(ngram.occur);
}
}
double lower_weight = interpolate ? discount.get_lower_weight(cur_stat) : 0.0;
//All ngrams with same context
for (int i = 0; i < vec_ngram.Count; i++)
{
Ngram ngram = vec_ngram[i];
if (ngram.word == null)
{
//skip unigram
continue;
}
if (ngram.occur >= g_min_count[order])
{
double prob = discount.get_discount(ngram.occur) / (double)cur_stat.m_total;
sw.WriteLine("{0} {1}\t{2} {3}", context, ngram.word, prob, lower_weight);
}
}
}
public static Discount[] g_discounts = new Discount[LM_ORDER]; ///< discounts parameter
///
/**
* load the unigram statistics and discount constants from file
*
* @param file, file name
* @param g_uni_stat, unigram statistics
* @param discounts, n-gram discount constants
*
*/
static bool LoadStatFile(string file, NgramStat g_uni_stat, Discount[] discounts)
{
StreamReader sr = new StreamReader(file);
string strLine = sr.ReadLine();
int pIndex = strLine.IndexOf('\t');
string[] items = strLine.Substring(pIndex + 1).Split();
g_uni_stat.m_total = long.Parse(items[0]);
g_uni_stat.m_min1 = long.Parse(items[1]);
g_uni_stat.m_min2 = long.Parse(items[2]);
g_uni_stat.m_min3 = long.Parse(items[3]);
Console.WriteLine("Total:{0} Min1:{1} Min2:{2} Min3:{3}", g_uni_stat.m_total, g_uni_stat.m_min1, g_uni_stat.m_min2, g_uni_stat.m_min3);
int order = 0;
while (sr.EndOfStream == false)
{
strLine = sr.ReadLine();
if (strLine.Length == 0)
{
continue;
}
pIndex = strLine.IndexOf('\t');
items = strLine.Substring(pIndex + 1).Split();
discounts[order] = new Discount();
discounts[order].m_d1 = double.Parse(items[0]);
discounts[order].m_d2 = double.Parse(items[1]);
discounts[order].m_d3plus = double.Parse(items[2]);
order++;
}
sr.Close();
return(order > 0);
}
const int LM_MINSCORE = -99; ///< minimal score for unknown word
//calculate the unigram prob and output it, the prob of BOS is 0
static void calc_unigram(string word, long occur, NgramStat stat, Discount discount, StreamWriter sw)
{
//set the prob=0 for LM_BOS <s>
if (word == LM_BOS)
{
double exponent = (double)LM_MINSCORE * Math.Log(10.0);
sw.WriteLine("{0}\t{1} 0", word, Math.Exp(exponent));
return;
}
//skip 1-gram with occur = 0
if (occur <= 0)
{
return;
}
double prob = discount.get_discount(occur) / (double)stat.m_total;
// normalize unigram, make sure sum(prob_unigram) = 1
prob += discount.get_lower_weight(stat) / (double)stat.m_min1;
sw.WriteLine("{0}\t{1} 0", word, prob);
}
