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/* Copyright (C) 2002 Univ. of Massachusetts Amherst, Computer Science Dept.
   This file is part of "MALLET" (MAchine Learning for LanguagE Toolkit).
   http://www.cs.umass.edu/~mccallum/mallet
   This software is provided under the terms of the Common Public License,
   version 1.0, as published by http://www.opensource.org.  For further
   information, see the file `LICENSE' included with this distribution. */




/** 
   @author Andrew McCallum [email protected]
 */

package cc.mallet.optimize;

import java.util.logging.*;

import cc.mallet.optimize.LineOptimizer;
import cc.mallet.optimize.Optimizable;
import cc.mallet.types.MatrixOps;
import cc.mallet.util.MalletLogger;

// Conjugate Gradient, Polak and Ribiere version
// from "Numeric Recipes in C", Section 10.6.

public class ConjugateGradient implements Optimizer
{
	private static Logger logger = MalletLogger.getLogger(ConjugateGradient.class.getName());
	
	boolean converged = false;
	Optimizable.ByGradientValue optimizable;
	LineOptimizer.ByGradient lineMaximizer;

	double initialStepSize = 1;
	double tolerance = 0.0001;
	double gradientTolerance = 0.001;
	int maxIterations = 1000;

	// "eps" is a small number to recitify the special case of converging
	// to exactly zero function value
	final double eps = 1.0e-10;
  private OptimizerEvaluator.ByGradient eval;

  public ConjugateGradient (Optimizable.ByGradientValue function, double initialStepSize)
  {
    this.initialStepSize = initialStepSize;
    this.optimizable = function;
    this.lineMaximizer = new BackTrackLineSearch (function);
    //Alternative:
    //this.lineMaximizer = new GradientBracketLineOptimizer (function);
  }

	public ConjugateGradient (Optimizable.ByGradientValue function)
	{
		this (function, 0.01);
	}

	public Optimizable getOptimizable () { return this.optimizable; }
	public boolean isConverged () { return converged; }

  public void setEvaluator (OptimizerEvaluator.ByGradient eval)
  {
    this.eval = eval;
  }

  public void setLineMaximizer (LineOptimizer.ByGradient lineMaximizer)
  {
    this.lineMaximizer = lineMaximizer;
  }

  public void setInitialStepSize (double initialStepSize) { this.initialStepSize = initialStepSize; }
	public double getInitialStepSize () { return this.initialStepSize; }
  public double getStepSize () { return step; }

  // The state of a conjugate gradient search
	double fp, gg, gam, dgg, step, fret;
	double[] xi, g, h;
	int j, iterations;

	public boolean optimize ()
	{
		return optimize (maxIterations);
	}

	public void setTolerance(double t) {
		tolerance = t;
	}

	public boolean optimize (int numIterations)
	{
		if (converged)
			return true;
    int n = optimizable.getNumParameters();
    if (xi == null) {
			fp = optimizable.getValue ();
			xi = new double[n];
			g = new double[n];
			h = new double[n];
			optimizable.getValueGradient (xi);
			System.arraycopy (xi, 0, g, 0, n);
			System.arraycopy (xi, 0, h, 0, n);
			step = initialStepSize;
      iterations = 0;
		}

		for (int iterationCount = 0; iterationCount < numIterations; iterationCount++) {
			logger.info ("ConjugateGradient: At iteration "+iterations+", cost = "+fp);
			
      step = lineMaximizer.optimize (xi, step);
      fret = optimizable.getValue();
      optimizable.getValueGradient(xi);
      
			// This termination provided by "Numeric Recipes in C".
			if (2.0*Math.abs(fret-fp) <= tolerance*(Math.abs(fret)+Math.abs(fp)+eps)) {
			  logger.info("ConjugateGradient converged: old value= "+fp+" new value= "+fret+" tolerance="+tolerance);
        converged = true;
        return true;
      }
      fp = fret;

			// This termination provided by McCallum
      double twoNorm = MatrixOps.twoNorm(xi);
			if (twoNorm < gradientTolerance) {
        logger.info("ConjugateGradient converged: gradient two norm " + twoNorm
                            +", less than " + gradientTolerance);
        converged = true;
        return true;
      }

      dgg = gg = 0.0;
			for (j = 0; j < xi.length; j++) {
				gg += g[j] * g[j];
				dgg += xi[j] * (xi[j] - g[j]);
			}
      gam = dgg/gg;

			for (j = 0; j < xi.length; j++) {
				g[j] = xi[j];
				h[j] = xi[j] + gam * h[j];
			}
			assert (!MatrixOps.isNaN(h));
			
      // gdruck
      // Mallet line search algorithms stop search whenever
      // a step is found that increases the value significantly.  
			// ConjugateGradient assumes that line maximization finds something close
      // to the maximum in that direction.  In tests, sometimes the
      // direction suggested by CG was downhill.  Consequently, here I am
      // setting the search direction to the gradient if the slope is
      // negative or 0.
			if (MatrixOps.dotProduct(xi, h) > 0) {
	      MatrixOps.set (xi, h);
			}
			else {
			  logger.warning("Reverting back to GA");
			  MatrixOps.set (h, xi);
			}

      iterations++;
			if (iterations > maxIterations) {
				logger.info("Too many iterations in ConjugateGradient.java");
				converged = true;
				return true;
			}

      if (eval != null) {
        eval.evaluate (optimizable, iterations);
      }
    }
		return false;
	}

  public void reset () { xi = null; }
}