com.expleague.ml.loss.ShiftedLLLogit Maven / Gradle / Ivy
package com.expleague.ml.loss;
import com.expleague.commons.math.vectors.impl.vectors.ArrayVec;
import com.expleague.commons.math.vectors.Vec;
import com.expleague.ml.data.set.DataSet;
import static java.lang.Math.exp;
import static java.lang.Math.log;
/**
* Created by irlab on 13.02.2015.
*/
public class ShiftedLLLogit extends LLLogit {
private Vec step1Scores;
public ShiftedLLLogit(final Vec target, final DataSet> owner) {
this(target, owner, new ArrayVec(target.dim()));
}
public ShiftedLLLogit(final Vec target, final DataSet> owner, final Vec step1Scores) {
super(target, owner);
this.step1Scores = step1Scores;
}
public void setStep1Scores(final Vec step1Scores) {
this.step1Scores = step1Scores;
}
@Override
public Vec gradient(final Vec x) {
final Vec result = new ArrayVec(x.dim());
for (int i = 0; i < x.dim(); i++) {
final double X = step1Scores.get(i) + x.get(i);
final double expX = exp(X);
final double pX = expX / (1 + expX);
if (target.get(i) > 0) // positive example
result.set(i, pX - 1);
else // negative
result.set(i, pX);
}
return result;
}
@Override
public double value(final Vec point) {
double result = 0;
for (int i = 0; i < point.dim(); i++) {
final double X = step1Scores.get(i) + point.get(i);
final double expMX = exp(-X);
final double pX = 1. / (1. + expMX);
if (target.get(i) > 0) // positive example
result += log(pX);
else // negative
result += log(1 - pX);
}
return exp(result / point.dim());
}
}
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