abstractcachingdifffunction.java

Standord Classifier实现了一个基于Java的最大熵分类器。用于模式识别

package edu.stanford.nlp.optimization;

import java.util.*;

/** @author Dan Klein */

public abstract class AbstractCachingDiffFunction implements DiffFunction, HasInitial {

  double[] lastX = null;

  protected double[] derivative = null;
  protected double value = 0.0;

  abstract public int domainDimension();

  abstract protected void calculate(double[] x);

  public double[] initial() {
    double[] initial = new double[domainDimension()];
    Arrays.fill(initial, 0.0);
    return initial;
  }

  void copy(double[] y, double[] x) {
    System.arraycopy(x, 0, y, 0, x.length);
  }

  void ensure(double[] x) {
    if (Arrays.equals(x, lastX))
      return;
    if (lastX == null)
      lastX = new double[domainDimension()];
    if (derivative == null)
      derivative = new double[domainDimension()];
    copy(lastX, x);
    calculate(x);
  }

  public double valueAt(double[] x) {
    ensure(x);
    return value;
  }

  double norm2(double[] x) {
    double sum = 0.0;
    for (int i=0; i<x.length; i++)
      sum += x[i]*x[i];
    return Math.sqrt(sum);
  }

  public double[] derivativeAt(double[] x) {
    ensure(x);
    return derivative;
  }
}