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/*
* LingPipe v. 4.1.0
* Copyright (C) 2003-2011 Alias-i
*
* This program is licensed under the Alias-i Royalty Free License
* Version 1 WITHOUT ANY WARRANTY, without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the Alias-i
* Royalty Free License Version 1 for more details.
*
* You should have received a copy of the Alias-i Royalty Free License
* Version 1 along with this program; if not, visit
* http://alias-i.com/lingpipe/licenses/lingpipe-license-1.txt or contact
* Alias-i, Inc. at 181 North 11th Street, Suite 401, Brooklyn, NY 11211,
* +1 (718) 290-9170.
*/
package com.aliasi.hmm;
import com.aliasi.symbol.SymbolTable;
/**
* An AbstractHmm is an abstract implementation of a
* hidden Markov model which manages a symbol table and defines the
* basic methods in terms of the symbolic linear probability methods.
* Specifically, the following four methods must be implemented by
* subclasses:
*
*
* Abstract Methods to Implement {@link #startProb(String)}
* {@link #endProb(String)} {@link #transitProb(String,String)}
* {@link #emitProb(String,CharSequence)}
*
* For efficiency, the log- and identifier-based versions of these
* methods may also be overridden. The symbol table is provided to
* the constructor and managed by this class.
*
* @author Bob Carpenter
* @version 2.2
* @since LingPipe2.1
*/
public abstract class AbstractHmm implements HiddenMarkovModel {
private final SymbolTable mStateSymbolTable;
/**
* Construct an HMM with the specified symbol table.
*
* @param stateSymbolTable Symbol table for the HMM.
*/
public AbstractHmm(SymbolTable stateSymbolTable) {
mStateSymbolTable = stateSymbolTable;
}
/**
* Adds the state with the specified name to this hidden Markov
* model.
*
* @param state Name of state to add.
* @return true if the state was not already a state
* in this HMM.
*/
public boolean addState(String state) {
if (mStateSymbolTable.symbolToID(state) >= 0) return false;
mStateSymbolTable.getOrAddSymbol(state);
return true;
}
/**
* Return the symbol table for the states for this HMM. This is
* the actual symbol table used by this HMM and changes to it
* affect this HMM.
*
* @return The symbol table for the states for this HMM.
*/
public SymbolTable stateSymbolTable() {
return mStateSymbolTable;
}
/**
* Returns the start probability for the specified state.
*
* @param state HMM state.
* @return Start probability of specified state.
*/
public abstract double startProb(String state);
/**
* Returns the start probability for the state with the specified
* identifier.
*
* This method is implemented in terms of {@link #stateSymbolTable()}
* and {@link #startProb(String)}.
*
* @param stateId Identifier of state.
* @return Start probability of state with specified identifier.
*/
public double startProb(int stateId) {
String state = stateSymbolTable().idToSymbol(stateId);
return startProb(state);
}
/**
* Returns the log (base 2) of the start probability for the
* specified state.
*
*
This method is implemented in terms of {@link
* com.aliasi.util.Math#log2(double)} and {@link
* #startProb(String)}.
*
* @param state HMM State.
* @return Log start probability of state.
*/
public double startLog2Prob(String state) {
return com.aliasi.util.Math.log2(startProb(state));
}
/**
* Returns the log (base 2) of the start probability for the
* state with the specified identifier.
*
*
This method is implemented in terms of {@link
* com.aliasi.util.Math#log2(double)} and {@link #startProb(int)}.
*
* @param stateId Identifier of state.
* @return Start probability of state with specified identifier.
*/
public double startLog2Prob(int stateId) {
return com.aliasi.util.Math.log2(startProb(stateId));
}
/**
* Returns the end probability for the specified state.
*
* @param state HMM state.
* @return End probability of specified state.
*/
public abstract double endProb(String state);
/**
* Returns the end probability for the state with the specified
* identifier.
*
*
This method is implemented with {@link #stateSymbolTable()} and
* and {@link #endProb(String)}.
*
* @param stateId Identifier of state.
* @return End probability of state with specified identifier.
*/
public double endProb(int stateId) {
String state = stateSymbolTable().idToSymbol(stateId);
if (stateId < 0) return 0.0;
return endProb(state);
}
/**
* Returns the log (base 2) of the end probability for the
* specified state.
*
*
This method is implemented in terms of {@link
* com.aliasi.util.Math#log2(double)} and {@link #endProb(String)}
*
* @param state HMM State.
* @return Log end probability of state.
*/
public double endLog2Prob(String state) {
return com.aliasi.util.Math.log2(endProb(state));
}
/**
* Returns the log (base 2) of the end probability for the
* state with the specified identifier.
*
*
This method is implemented in terms of {@link
* com.aliasi.util.Math#log2(double)} and {@link #endProb(int)}
*
* @param stateId Identifier of state.
* @return End probability of state with specified identifier.
*/
public double endLog2Prob(int stateId) {
return com.aliasi.util.Math.log2(endProb(stateId));
}
/**
* Returns an estimate of a transition from the source state with
* the specified name to the target state with the specified
* label.
*
* @param source Label of source state.
* @param target Label of target state.
* @return Estimate of likelihood of transition from the source
* to the target state.
*/
public abstract double transitProb(String source, String target);
/**
* Return an estimate of the transition likelihood from the source
* state with the specified identifier to the target state with the
* specified identifier.
*
*
This method is implemented in terms of {@link #stateSymbolTable()}
* and {@link #transitProb(String,String)}.
*
* @param sourceId Source state identifier.
* @param targetId Target state identifier.
* @return Estimate of the transition probability.
*/
public double transitProb(int sourceId, int targetId) {
return transitProb(mStateSymbolTable.idToSymbol(sourceId),
mStateSymbolTable.idToSymbol(targetId));
}
/**
* Returns the log (base 2) estimate of a transition probability.
* See {@link #transitProb(String,String)} for more information.
*
*
This method is implemented in terms of {@link
* com.aliasi.util.Math#log2(double)} and {@link
* #transitProb(String,String)}.
*
* @param source Label of source state.
* @param target Label of target state.
* @return Log (base 2) Estimate of likelihood of transition from
* the source to the target state.
*/
public double transitLog2Prob(String source, String target) {
return com.aliasi.util.Math.log2(transitProb(source,target));
}
/**
* Returns the log (base 2) of the transition estimate. See
* {@link #transitProb(int,int)} for more information.
*
*
This method is implemented in terms of {@link
* com.aliasi.util.Math#log2(double)} and {@link
* #transitProb(int,int)}
*
* @param sourceId Source state identifier.
* @param targetId Target state identifier.
* @return Estimate of the transition probability.
*/
public double transitLog2Prob(int sourceId, int targetId) {
return com.aliasi.util.Math.log2(transitProb(sourceId,targetId));
}
/**
* Returns an estimate the emission of the specified string
* by the state with the specified label.
*
* @param state Label of state.
* @param emission Character sequence emitted.
* @return Estimate of likelihood of the state emitting the
* string.
*/
public abstract double emitProb(String state, CharSequence emission);
/**
* Return an estimate of the likelihood of the state with the
* specified identifier to emit the specified string.
*
*
This method is implemented in terms of {@link
* #emitProb(String,CharSequence)}.
*
* @param stateId State identifier.
* @param emission Character sequence emitted.
* @return Estimate of probability of the specified state emitting the
* specified string.
*/
public double emitProb(int stateId, CharSequence emission) {
return emitProb(mStateSymbolTable.idToSymbol(stateId),emission);
}
/**
* Return the log (base 2) of the emission estimate. See
* {@link #emitProb(int,CharSequence)} for more details.
*
*
This method is implemented in terms of {@link
* com.aliasi.util.Math#log2(double)} and {@link
* #emitProb(int,CharSequence)}.
*
* @param stateId State identifier.
* @param emission Character sequence emitted.
* @return Log (base 2) estimate of probability of the specified
* state emitting the specified string.
*/
public double emitLog2Prob(int stateId, CharSequence emission) {
return com.aliasi.util.Math.log2(emitProb(stateId,emission));
}
/**
* Returns the log (base 2) of the emission estimate. See
* {@link #emitProb(String,CharSequence)} for more information.
*
*
This method is implemented in terms of {@link
* com.aliasi.util.Math#log2(double)} and {@link
* #emitProb(String,CharSequence)}.
*
* @param state Label of state.
* @param emission Character sequence emitted.
* @return Log (base 2) estimate of likelihood of the state
* emitting the string.
*/
public double emitLog2Prob(String state, CharSequence emission) {
return com.aliasi.util.Math.log2(emitProb(state,emission));
}
}