Bernoulli.java

/*******************************************************************************
*   Copyright 2013 Analog Devices, Inc.
*
*   Licensed under the Apache License, Version 2.0 (the "License");
*   you may not use this file except in compliance with the License.
*   You may obtain a copy of the License at
*
*       http://www.apache.org/licenses/LICENSE-2.0
*
*   Unless required by applicable law or agreed to in writing, software
*   distributed under the License is distributed on an "AS IS" BASIS,
*   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
*   See the License for the specific language governing permissions and
*   limitations under the License.
********************************************************************************/

package com.analog.lyric.dimple.factorfunctions;

import java.util.Map;

import org.eclipse.jdt.annotation.Nullable;

import com.analog.lyric.dimple.exceptions.DimpleException;
import com.analog.lyric.dimple.factorfunctions.core.FactorFunctionUtilities;
import com.analog.lyric.dimple.factorfunctions.core.IParametricFactorFunction;
import com.analog.lyric.dimple.factorfunctions.core.UnaryFactorFunction;
import com.analog.lyric.dimple.model.values.Value;


/**
 * Parameterized Bernoulli distribution, which corresponds to p(x | p),
 * where p is the probability parameter
 * 
 * The conjugate prior for p is a Beta distribution.
 * Depending on the solver, it may or may not be necessary to use a
 * conjugate prior (for the Gibbs solver, for example, it is not).
 * 
 * The variables in the argument list are ordered as follows:
 * 
 * 1) p: Probability parameter
 * 2...) An arbitrary number of discrete output variable (MUST be zero-based integer values [e.g., Bit variable]) 	// TODO: remove this restriction
 * 
 * The parameter may optionally be specified as a constant in the constructor.
 * In this case, the parameter is not included in the list of arguments.
 */
public class Bernoulli extends UnaryFactorFunction implements IParametricFactorFunction
{
	private static final long serialVersionUID = 1L;

	private double _p;
	private boolean _parametersConstant;
	private int _firstDirectedToIndex;
	
	/*--------------
	 * Construction
	 */
	
	public Bernoulli()		// Variable parameter
	{
		super((String)null);
		_parametersConstant = false;
		_firstDirectedToIndex = 1;
	}
	
	/**
	 * @since 0.05
	 */
	public Bernoulli(double p)	// Constant parameter
	{
		this();
		_p = p;
		_parametersConstant = true;
		_firstDirectedToIndex = 0;
		if (p < 0 || p > 1) throw new DimpleException("Invalid parameter value.  Must be in range [0, 1].");
	}
	
	/**
	 * Constructs with fixed probability parameter.
	 * @param parameterMap specifies the Bernoulli parameter in the entry with the key "p".
	 * If there is no such entry, the parameter will default to .5.
	 * @since 0.07
	 */
	public Bernoulli(Map<String,Object> parameterMap)
	{
		this((double)getOrDefault(parameterMap, "p", .5));
	}

	protected Bernoulli(Bernoulli other)
	{
		super(other);
		_p = other._p;
		_parametersConstant = other._parametersConstant;
		_firstDirectedToIndex = other._firstDirectedToIndex;
	}
	
	@Override
	public Bernoulli clone()
	{
		return new Bernoulli(this);
	}
	
	/*----------------
	 * IDatum methods
	 */
	
	@Override
	public boolean objectEquals(@Nullable Object other)
	{
		if (this == other)
		{
			return true;
		}
		
		if (other instanceof Bernoulli)
		{
			Bernoulli that = (Bernoulli)other;
			return _p == that._p &&
				_parametersConstant == that._parametersConstant &&
				_firstDirectedToIndex == that._firstDirectedToIndex;
		}
		
		return false;
	}
	
	/*-------------------------
	 *  FactorFunction methods
	 */
	
	
    @Override
	public final double evalEnergy(Value[] arguments)
    {
    	double p;
    	if (_parametersConstant)
    	{
    		p = _p;
    	}
    	else
    	{
    		p = arguments[0].getDouble();								// First argument, if present, is parameter, p
    		if (p < 0 || p > 1) return Double.POSITIVE_INFINITY;
    	}
		
		int numZeros = 0;
		final int length = arguments.length;
    	for (int i = _firstDirectedToIndex; i < length; i++)
    	{
    		int x = arguments[i].getInt();								// Remaining arguments are Discrete or Bit variables
    		if (x == 0) numZeros++;
    	}
		final int N = length - _firstDirectedToIndex;					// Number of non-parameter variables
    	final int numOnes = N - numZeros;
    	

    	if (p == 0)
    		if (numOnes > 0)
    			return Double.POSITIVE_INFINITY;
    		else
    			return 0;
    	else if (p == 1)
    		if (numZeros > 0)
    			return Double.POSITIVE_INFINITY;
    		else
    			return 0;
    	else
    		return -(numOnes * Math.log(p) + numZeros * Math.log(1-p));
	}
    
    @Override
    public final boolean isDirected() {return true;}
    @Override
	public final int[] getDirectedToIndices(int numEdges)
	{
    	// All edges except the parameter edges (if present) are directed-to edges
		return FactorFunctionUtilities.getListOfIndices(_firstDirectedToIndex, numEdges-1);
	}
    
    /*-----------------------------------
     * IParametricFactorFunction methods
     */
    
    @Override
    public int copyParametersInto(Map<String, Object> parameters)
    {
    	if (_parametersConstant)
    	{
    		parameters.put("p", _p);
    		return 1;
    	}
    	else
    	{
    		return 0;
    	}
    }
    
    @Override
    public @Nullable Object getParameter(String parameterName)
    {
    	if (_parametersConstant)
    	{
    		switch (parameterName)
    		{
    		case "p":
    			return _p;
    		}
    	}
    	return null;
    }
    
    @Override
	public final boolean hasConstantParameters()
    {
    	return _parametersConstant;
    }

    /*--------------------------
     * Factor-specific methods
     */
    
    public final double getParameter()
    {
    	return _p;
    }
}