/*
* 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.flink.examples.java.misc;
import org.apache.flink.api.common.functions.MapFunction;
import org.apache.flink.api.common.functions.ReduceFunction;
import org.apache.flink.api.java.DataSet;
import org.apache.flink.api.java.ExecutionEnvironment;
/**
* Estimates the value of Pi using the Monte Carlo method.
* The area of a circle is Pi * R^2, R being the radius of the circle
* The area of a square is 4 * R^2, where the length of the square's edge is 2*R.
*
* Thus Pi = 4 * (area of circle / area of square).
*
* The idea is to find a way to estimate the circle to square area ratio.
* The Monte Carlo method suggests collecting random points (within the square)
* and then counting the number of points that fall within the circle
*
* <pre>
* {@code
* x = Math.random()
* y = Math.random()
*
* x * x + y * y < 1
* }
* </pre>
*/
@SuppressWarnings("serial")
public class PiEstimation implements java.io.Serializable {
public static void main(String[] args) throws Exception {
final long numSamples = args.length > 0 ? Long.parseLong(args[0]) : 1000000;
final ExecutionEnvironment env = ExecutionEnvironment.getExecutionEnvironment();
// count how many of the samples would randomly fall into
// the unit circle
DataSet<Long> count =
env.generateSequence(1, numSamples)
.map(new Sampler())
.reduce(new SumReducer());
long theCount = count.collect().get(0);
System.out.println("We estimate Pi to be: " + (theCount * 4.0 / numSamples));
}
//*************************************************************************
// USER FUNCTIONS
//*************************************************************************
/**
* Sampler randomly emits points that fall within a square of edge x * y.
* It calculates the distance to the center of a virtually centered circle of radius x = y = 1
* If the distance is less than 1, then and only then does it returns a 1.
*/
public static class Sampler implements MapFunction<Long, Long> {
@Override
public Long map(Long value) {
double x = Math.random();
double y = Math.random();
return (x * x + y * y) < 1 ? 1L : 0L;
}
}
/**
* Simply sums up all long values.
*/
public static final class SumReducer implements ReduceFunction<Long>{
@Override
public Long reduce(Long value1, Long value2) {
return value1 + value2;
}
}
}