edu.berkeley.nlp.lm

Class StupidBackoffLm<W>

java.lang.Object

edu.berkeley.nlp.lm.AbstractNgramLanguageModel<W>

edu.berkeley.nlp.lm.AbstractArrayEncodedNgramLanguageModel<W>

edu.berkeley.nlp.lm.StupidBackoffLm<W>

Type Parameters:

W -

All Implemented Interfaces:

ArrayEncodedNgramLanguageModel<W>, NgramLanguageModel<W>, java.io.Serializable

public class StupidBackoffLm<W>
extends AbstractArrayEncodedNgramLanguageModel<W>
implements ArrayEncodedNgramLanguageModel<W>, java.io.Serializable

Language model implementation which uses stupid backoff (Brants et al., 2007) computation. Note that stupid backoff does not properly normalize, so the scores this LM computes are not in fact probabilities. Also, unliked LMs estimated using LmReaders.createKneserNeyLmFromTextFiles, this model returns natural logarithms instead of log10.

Author:

adampauls

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from interface edu.berkeley.nlp.lm.ArrayEncodedNgramLanguageModel

ArrayEncodedNgramLanguageModel.DefaultImplementations

Nested classes/interfaces inherited from interface edu.berkeley.nlp.lm.NgramLanguageModel

NgramLanguageModel.StaticMethods

Field Summary

Fields

Modifier and Type	Field and Description
protected NgramMap<LongRef>	map

Fields inherited from class edu.berkeley.nlp.lm.AbstractNgramLanguageModel

lmOrder, oovWordLogProb

Constructor Summary

Constructors

Constructor and Description
StupidBackoffLm(int lmOrder, WordIndexer<W> wordIndexer, NgramMap<LongRef> map, ConfigOptions opts)

Method Summary

Modifier and Type	Method and Description
float	getLogProb(int[] ngram) Equivalent to getLogProb(ngram, 0, ngram.length)
float	getLogProb(int[] ngram, int startPos, int endPos) Calculate language model score of an n-gram.
float	getLogProb(java.util.List<W> ngram) Scores an n-gram.
NgramMap<LongRef>	getNgramMap()
long	getRawCount(int[] ngram, int startPos, int endPos) Gets the raw count of an n-gram.

Methods inherited from class edu.berkeley.nlp.lm.AbstractArrayEncodedNgramLanguageModel

scoreSentence

Methods inherited from class edu.berkeley.nlp.lm.AbstractNgramLanguageModel

getLmOrder, getWordIndexer, setOovWordLogProb

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface edu.berkeley.nlp.lm.NgramLanguageModel

getLmOrder, getWordIndexer, scoreSentence, setOovWordLogProb

Field Detail

map

protected final NgramMap<LongRef> map

Constructor Detail

StupidBackoffLm

public StupidBackoffLm(int lmOrder,
                       WordIndexer<W> wordIndexer,
                       NgramMap<LongRef> map,
                       ConfigOptions opts)

Method Detail

getLogProb

public float getLogProb(int[] ngram,
                        int startPos,
                        int endPos)

Description copied from interface: ArrayEncodedNgramLanguageModel

Calculate language model score of an n-gram. Warning: if you pass in an n-gram of length greater than getLmOrder(), this call will silently ignore the extra words of context. In other words, if you pass in a 5-gram (endPos-startPos == 5) to a 3-gram model, it will only score the words from startPos + 2 to endPos.

Specified by:

getLogProb in interface ArrayEncodedNgramLanguageModel<W>

Specified by:

getLogProb in class AbstractArrayEncodedNgramLanguageModel<W>

Parameters:

ngram - array of words in integer representation

startPos - start of the portion of the array to be read

endPos - end of the portion of the array to be read.

Returns:

getRawCount

public long getRawCount(int[] ngram,
                        int startPos,
                        int endPos)

Gets the raw count of an n-gram.

Parameters:

ngram -

startPos -

endPos -

Returns:

count of n-gram, or -1 if n-gram is not in the map.

getLogProb

public float getLogProb(int[] ngram)

Description copied from interface: ArrayEncodedNgramLanguageModel

Equivalent to getLogProb(ngram, 0, ngram.length)

Specified by:

getLogProb in interface ArrayEncodedNgramLanguageModel<W>

Overrides:

getLogProb in class AbstractArrayEncodedNgramLanguageModel<W>

See Also:

ArrayEncodedNgramLanguageModel.getLogProb(int[], int, int)

getLogProb

public float getLogProb(java.util.List<W> ngram)

Description copied from interface: NgramLanguageModel

Scores an n-gram. This is a convenience method and will generally be relatively inefficient. More efficient versions are available in ArrayEncodedNgramLanguageModel.getLogProb(int[], int, int) and ContextEncodedNgramLanguageModel.getLogProb(long, int, int, edu.berkeley.nlp.lm.ContextEncodedNgramLanguageModel.LmContextInfo) .

Specified by:

getLogProb in interface NgramLanguageModel<W>

Overrides:

getLogProb in class AbstractArrayEncodedNgramLanguageModel<W>

getNgramMap

public NgramMap<LongRef> getNgramMap()