/*******************************************************************************
*   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.factorfunctions;

import com.analog.lyric.dimple.factorfunctions.core.FactorFunction;
import com.analog.lyric.dimple.model.values.Value;


/**
 * Deterministic constant power function.
 * <p>
 * The constant power value is
 * specified in the constructor.  This is a deterministic directed factor
 * (if smoothing is not enabled).
 * <p>
 * Optional smoothing may be applied, by providing a smoothing value in
 * the constructor. If smoothing is enabled, the distribution is
 * smoothed by exp(-difference^2/smoothing), where difference is the
 * distance between the output value and the deterministic output value
 * for the corresponding inputs.
 * <p>
 * The variables are ordered as follows in the argument list:
 * <ol>
 * <li> Output (Output = Base^Power)
 * <li> Base (double or integer)
 * </ol>
 * 
 * Note: This factor is not compatible with negative values of Base with
 * fractional values of Power, which would result in a complex output.
 * 
 */
public class ConstantPower extends FactorFunction
{
	protected double _power;
	protected double _beta = 0;
	protected boolean _smoothingSpecified = false;
	public ConstantPower(double power) {this(power, 0);}
	public ConstantPower(double power, double smoothing)
	{
		super();
		_power = power;
		if (smoothing > 0)
		{
			_beta = 1 / smoothing;
			_smoothingSpecified = true;
		}
	}
	
    @Override
    public final double evalEnergy(Value[] arguments)
    {
    	final double result = arguments[0].getDouble();
    	final double base = arguments[1].getDouble();
    	
    	final double computedResult = Math.pow(base, _power);
    	
    	if (_smoothingSpecified)
    	{
    		final double diff = computedResult - result;
    		final double potential = diff*diff;
    		return potential*_beta;
    	}
    	else
    	{
    		return (computedResult == result) ? 0 : Double.POSITIVE_INFINITY;
    	}
    }
    
    
    @Override
    public final boolean isDirected() {return true;}
    @Override
	public final int[] getDirectedToIndices() {return new int[]{0};}
    @Override
	public final boolean isDeterministicDirected() {return !_smoothingSpecified;}
    @Override
	public final void evalDeterministic(Value[] arguments)
    {
    	final Double base = arguments[1].getDouble();
    	arguments[0].setDouble(Math.pow(base, _power));		// Replace the output value
    }
}