CustomFiniteFieldProjection.java

/*******************************************************************************
*   Copyright 2012 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.solvers.sumproduct.customFactors;

import java.util.List;

import com.analog.lyric.dimple.exceptions.DimpleException;
import com.analog.lyric.dimple.model.factors.Factor;
import com.analog.lyric.dimple.model.values.Value;
import com.analog.lyric.dimple.model.variables.Discrete;
import com.analog.lyric.dimple.solvers.sumproduct.SFiniteFieldFactor;
import com.analog.lyric.dimple.solvers.sumproduct.SumProductFiniteFieldVariable;
import com.analog.lyric.dimple.solvers.sumproduct.SumProductSolverGraph;

@SuppressWarnings("deprecation") // TODO remove when SFiniteFieldFactor removed
public class CustomFiniteFieldProjection extends SFiniteFieldFactor
{

	private SumProductFiniteFieldVariable _ffVar;
	private int [] _portIndex2bitIndex;
	private int [] _bit2port;
	
	public CustomFiniteFieldProjection(Factor factor, SumProductSolverGraph parent)
	{
		super(factor, parent);

		final int nVars = factor.getSiblingCount();
		if (nVars <= 1)
			throw new DimpleException("need to specify at least one bit for projection");
		
		final int nEdges = factor.getSiblingCount();
		
		//First variable is the FiniteFieldVariable
		//Other variables should be bits.
		_ffVar = (SumProductFiniteFieldVariable)getSibling(0);
		_portIndex2bitIndex = new int[nEdges];
		
		for (int i = 0; i < nEdges; i++)
			_portIndex2bitIndex[i] = -1;
		
		//get constant value and make sure it's in range
		final List<Value> constants = factor.getConstantValues();
		if (constants.size()!= 1)
			throw new DimpleException("expected one constant to specify the array of bit positions");

		double [] domain = constants.get(0).getDoubleArray();
		
		if (nVars != 1+domain.length)
			throw new DimpleException("expect finite field variable, bit positions, and bits");

		
		_bit2port = new int[nEdges-1];
		
		for (int i = 1; i < nVars; i++)
		{
			//TODO: error check
			int index = (int)domain[i-1];
			
			if (index < 0 || index >= nEdges-1)
				throw new DimpleException("index out of range");
			if (_bit2port[index] != 0)
				throw new DimpleException("Tried to set index twice");
			
			//get Variable and make sure it's a bit.
			Discrete bit = (Discrete)factor.getSibling(i);
			
			Object [] bitDomain = bit.getDiscreteDomain().getElements();
			if (bitDomain.length != 2 || (Double)bitDomain[0] != 0 || (Double)bitDomain[1] != 1)
				throw new DimpleException("expected bit");
			
			_bit2port[index] = i;
			_portIndex2bitIndex[i] = index;
		}
	}

	@Override
	public void doUpdateEdge(int outPortNum)
	{
		if (outPortNum == 0)
			updateFiniteField();
		else
		{
			if (outPortNum >= 1)
				updateBit(outPortNum);
		}
	}
	
	public void updateFiniteField()
	{
		//for every value of the finite field
		double [] outputs = getSiblingEdgeState(0).factorToVarMsg.representation();
		int numBits = _ffVar.getNumBits();

		final int nEdges = getSiblingCount();
		
		double prod;
		double [][] inputMsgs = new double[numBits][];
		for (int i = 1; i < nEdges; i++)
		{
			inputMsgs[i-1] = getSiblingEdgeState(i).varToFactorMsg.representation();
		}
		
		//Multiply bit probabilities
		double sum = 0;
		
		for (int i = 0, end = ((Discrete)_ffVar.getVariable()).getDiscreteDomain().size(); i < end; i++)
		{
			prod = 1;
			for (int j = 0; j < numBits; j++)
			{
				int p = _bit2port[j];
				
				if (p != 0)
				{
					if (((i >> j) & 1) == 1)
					{
						//is one
						prod *= inputMsgs[j][1];
					}
					else
					{
						prod *= inputMsgs[j][0];
					}
				}
				
			}
			outputs[i] = prod;
			sum += prod;
		}
		
		//normalize
		for (int i = 0; i < outputs.length; i++)
			outputs[i] /= sum;

	}
	
	public void updateBit(int portNum)
	{
		
		//get output msg for bit
		double [] outputs = getSiblingEdgeState(portNum).factorToVarMsg.representation();
		
		//init to 1 for each
		outputs[0] = 0;
		outputs[1] = 0;
				
		int bit = _portIndex2bitIndex[portNum];
		
		//Iterate each value of finite field
		double [] inputs = getSiblingEdgeState(0).varToFactorMsg.representation();
		
		for (int i = 0; i < inputs.length; i++)
		{
			//extract value of bit of interest
			if (((i >> bit) & 1) == 1)
			{
				//bit was one
				outputs[1] += inputs[i];
			}
			else
			{
				//bit was zero
				outputs[0] += inputs[i];
			}
			
			
		}
		
		//normalize
		double sum = outputs[0]+outputs[1];
		outputs[0] /= sum;
		outputs[1] /= sum;
		
		
	}
}