content: /**
   * 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 org.apache.bigtop.datagenerators.samplers.samplers;
  
  import java.util.Random;
  
  import org.apache.bigtop.datagenerators.samplers.SeedFactory;
  import org.apache.bigtop.datagenerators.samplers.pdfs.ConditionalProbabilityDensityFunction;
  
  
  public class StatefulMonteCarloSampler<T> implements Sampler<T>
  {
  	private final Sampler<T> stateSampler;
  	private final Random rng;
  	private final ConditionalProbabilityDensityFunction<T, T> acceptancePDF;
  	private T currentState;
  
  	public StatefulMonteCarloSampler(Sampler<T> stateGenerator,
  			ConditionalProbabilityDensityFunction<T, T> acceptancePDF,
  			T initialState,
  			SeedFactory seedFactory)
  	{
  		this.acceptancePDF = acceptancePDF;
  		this.stateSampler = stateGenerator;
  
  		rng = new Random(seedFactory.getNextSeed());
  
  		this.currentState = initialState;
  	}
  
  	public T sample() throws Exception
  	{
  		while(true)
  		{
  			T proposedState = this.stateSampler.sample();
  			double probability = acceptancePDF.probability(proposedState, currentState);
  			double r = rng.nextDouble();
  
  			if(r < probability)
  			{
  				this.currentState = proposedState;
  				return proposedState;
  			}
  		}
  	}
  
  }
  