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/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 opennlp.tools.ml.maxent.quasinewton;
import java.lang.reflect.Constructor;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import opennlp.tools.ml.model.DataIndexer;
/**
* Evaluate negative log-likelihood and its gradient in parallel
*/
public class ParallelNegLogLikelihood extends NegLogLikelihood {
// Number of threads
private int threads;
// Partial value of negative log-likelihood to be computed by each thread
private double[] negLogLikelihoodThread;
// Partial gradient
private double[][] gradientThread;
public ParallelNegLogLikelihood(DataIndexer indexer, int threads) {
super(indexer);
if (threads <= 0)
throw new IllegalArgumentException(
"Number of threads must 1 or larger");
this.threads = threads;
this.negLogLikelihoodThread = new double[threads];
this.gradientThread = new double[threads][dimension];
}
/**
* Negative log-likelihood
*/
@Override
public double valueAt(double[] x) {
if (x.length != dimension)
throw new IllegalArgumentException(
"x is invalid, its dimension is not equal to domain dimension.");
// Compute partial value of negative log-likelihood in each thread
computeInParallel(x, NegLLComputeTask.class);
double negLogLikelihood = 0;
for (int t = 0; t < threads; t++) {
negLogLikelihood += negLogLikelihoodThread[t];
}
return negLogLikelihood;
}
/**
* Compute gradient
*/
@Override
public double[] gradientAt(double[] x) {
if (x.length != dimension)
throw new IllegalArgumentException(
"x is invalid, its dimension is not equal to the function.");
// Compute partial gradient in each thread
computeInParallel(x, GradientComputeTask.class);
// Accumulate gradient
for (int i = 0; i < dimension; i++) {
gradient[i] = 0;
for (int t = 0; t < threads; t++) {
gradient[i] += gradientThread[t][i];
}
}
return gradient;
}
/**
* Compute tasks in parallel
*/
private void computeInParallel(double[] x, Class taskClass) {
ExecutorService executor = Executors.newFixedThreadPool(threads);
int taskSize = numContexts / threads;
int leftOver = numContexts % threads;
try {
Constructor cons = taskClass.getConstructor(
ParallelNegLogLikelihood.class,
int.class, int.class, int.class, double[].class);
List> futures = new ArrayList<>();
for (int i = 0; i < threads; i++) {
if (i != threads - 1)
futures.add(executor.submit(
cons.newInstance(this, i, i * taskSize, taskSize, x)));
else
futures.add(executor.submit(
cons.newInstance(this, i, i * taskSize, taskSize + leftOver, x)));
}
for (Future future: futures)
future.get();
} catch (Exception e) {
e.printStackTrace();
}
executor.shutdown();
}
/**
* Task that is computed in parallel
*/
abstract class ComputeTask implements Callable {
final int threadIndex;
// Start index of contexts to compute
final int startIndex;
// Number of contexts to compute
final int length;
final double[] x;
public ComputeTask(int threadIndex, int startIndex, int length, double[] x) {
this.threadIndex = threadIndex;
this.startIndex = startIndex;
this.length = length;
this.x = x;
}
}
/**
* Task for computing partial value of negative log-likelihood
*/
class NegLLComputeTask extends ComputeTask {
final double[] tempSums;
public NegLLComputeTask(int threadIndex, int startIndex, int length, double[] x) {
super(threadIndex, startIndex, length, x);
this.tempSums = new double[numOutcomes];
}
@Override
public NegLLComputeTask call() {
int ci, oi, ai, vectorIndex, outcome;
double predValue, logSumOfExps;
negLogLikelihoodThread[threadIndex] = 0;
for (ci = startIndex; ci < startIndex + length; ci++) {
for (oi = 0; oi < numOutcomes; oi++) {
tempSums[oi] = 0;
for (ai = 0; ai < contexts[ci].length; ai++) {
vectorIndex = indexOf(oi, contexts[ci][ai]);
predValue = values != null ? values[ci][ai] : 1.0;
tempSums[oi] += predValue * x[vectorIndex];
}
}
logSumOfExps = ArrayMath.logSumOfExps(tempSums);
outcome = outcomeList[ci];
negLogLikelihoodThread[threadIndex] -=
(tempSums[outcome] - logSumOfExps) * numTimesEventsSeen[ci];
}
return this;
}
}
/**
* Task for computing partial gradient
*/
class GradientComputeTask extends ComputeTask {
final double[] expectation;
public GradientComputeTask(int threadIndex, int startIndex, int length, double[] x) {
super(threadIndex, startIndex, length, x);
this.expectation = new double[numOutcomes];
}
@Override
public GradientComputeTask call() {
int ci, oi, ai, vectorIndex;
double predValue, logSumOfExps;
int empirical;
// Reset gradientThread
Arrays.fill(gradientThread[threadIndex], 0);
for (ci = startIndex; ci < startIndex + length; ci++) {
for (oi = 0; oi < numOutcomes; oi++) {
expectation[oi] = 0;
for (ai = 0; ai < contexts[ci].length; ai++) {
vectorIndex = indexOf(oi, contexts[ci][ai]);
predValue = values != null ? values[ci][ai] : 1.0;
expectation[oi] += predValue * x[vectorIndex];
}
}
logSumOfExps = ArrayMath.logSumOfExps(expectation);
for (oi = 0; oi < numOutcomes; oi++) {
expectation[oi] = Math.exp(expectation[oi] - logSumOfExps);
}
for (oi = 0; oi < numOutcomes; oi++) {
empirical = outcomeList[ci] == oi ? 1 : 0;
for (ai = 0; ai < contexts[ci].length; ai++) {
vectorIndex = indexOf(oi, contexts[ci][ai]);
predValue = values != null ? values[ci][ai] : 1.0;
gradientThread[threadIndex][vectorIndex] +=
predValue * (expectation[oi] - empirical) * numTimesEventsSeen[ci];
}
}
}
return this;
}
}
}
