/*
 *  Calculation of Pi using quadrature realized with an approached based on evolving values in an array with
 *  implicit parallelism.  This is material that probably won't actually be in Java 7.
 *
 *  Copyright © 2009–2011 Russel Winder
 */

import extra166y.CommonOps ;
import extra166y.Ops ;
import extra166y.ParallelDoubleArray ;
import extra166y.ParallelDoubleArrayWithDoubleMapping ;

public class Pi_Java_ParallelArray {
  private static void execute ( final int numberOfTasks ) {
    final int n = 1000000000 ;
    final double delta = 1.0 / n ;
    final long startTimeNanos = System.nanoTime ( ) ;
    final int sliceSize = n / numberOfTasks ;
    final ParallelDoubleArray initialArray = ParallelDoubleArray.create ( numberOfTasks , ParallelDoubleArray.defaultExecutor ( ) ) ;
    final ParallelDoubleArrayWithDoubleMapping finalArray = initialArray.withIndexedMapping ( new Ops.IntAndDoubleToDouble ( ) {
        @Override public double op ( final int taskId , final double initialValue ) {
          final int start = 1 + taskId * sliceSize ;
          final int end = ( taskId + 1 ) * sliceSize ;
          double sum = 0.0 ;
          for ( int i = start ; i <= end ; ++i ) {
            final double x = ( i - 0.5 ) * delta ;
            sum += 1.0 / ( 1.0 + x * x ) ;
          }
          return sum ;
        }
      } ) ;
    final double pi = 4.0 * delta * finalArray.reduce ( CommonOps.doubleAdder ( ) , 0.0 ) ;
    final double elapseTime = ( System.nanoTime ( ) - startTimeNanos ) / 1e9 ;
    System.out.println ( "==== Java Parallel Array pi = " + pi ) ;
    System.out.println ( "==== Java Parallel Array iteration count = " + n ) ;
    System.out.println ( "==== Java Parallel Array elapse = " + elapseTime ) ;
    System.out.println ( "==== Java Parallel Array processor count = " + Runtime.getRuntime ( ).availableProcessors ( ) ) ;
    System.out.println ( "==== Java Parallel Array thread count = " + numberOfTasks ) ;
  }
  public static void main ( final String[] args ) {
    Pi_Java_ParallelArray.execute ( 1 ) ;
    System.out.println ( ) ;
    Pi_Java_ParallelArray.execute ( 2 ) ;
    System.out.println ( ) ;
    Pi_Java_ParallelArray.execute ( 8 ) ;
    System.out.println ( ) ;
    Pi_Java_ParallelArray.execute ( 32 ) ;
  }
}