edu.berkeley.nlp.math.LogAdder Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of berkeleyparser Show documentation

The Berkeley parser analyzes the grammatical structure of natural language using probabilistic context-free grammars (PCFGs).

The newest version!

package edu.berkeley.nlp.math;

public class LogAdder {
	boolean inited = false;
	double sum;
	boolean superSloppy;

	public LogAdder(boolean superSloppy) {
		super();
		this.superSloppy = superSloppy;
	}
	
	public LogAdder() {
		this(false);
	}

	public void logAdd(double logProb) {
		if (inited) {
			sum = sloppyLogAdd(sum, logProb);
			// sum += logProb;
		} else {
			inited = true;
			sum = logProb;
		}
	}

	public double sloppyLogAdd(double lx, double ly) {
		double max, negDiff;
		if (lx > ly) {
			max = lx;
			negDiff = ly - lx;
		} else {
			max = ly;
			negDiff = lx - ly;
		}
		if (max == Double.NEGATIVE_INFINITY) {
			return max;
		} else if (negDiff < -SloppyMath.LOGTOLERANCE) {
			return max;
		} else {
			if (superSloppy) {
				return max + SloppyMath.approxLog(1.0 + SloppyMath.approxExp(negDiff));
			}
			return max + Math.log(1.0 + Math.exp(negDiff));
		}
	}

	public double getSum() {
		return inited ? sum : Double.NEGATIVE_INFINITY;
	}
}