PI parallel computation

gistfile1.go

// Parallel algorithm for PI calculation
//
// Sources of inspiration:
//
// * https://computing.llnl.gov/tutorials/parallel_comp/#ExamplesPI
// * http://dos.iitm.ac.in/Vishwa/GCCourse/suneetha/picalc.html
//
// Thanks to aht for fixing the random generator issue:
// http://groups.google.com/group/golang-nuts/browse_thread/thread/f5c12ca69b46a931

package main

import (
	"rand"
	"time"
	"flag"
	"fmt"
)

func getCoord(rg *rand.Rand) float64 {
	return -1 + rg.Float64()
}

func calcPartialPI(result chan<- float64, iter int) {
	var circle, i int

	rg := rand.New(rand.NewSource(time.Nanoseconds() % 1e9))

	for i = 0; i < iter; i++ {
		x, y := getCoord(rg), getCoord(rg)
		if (x*x + y*y) < 1.0 {
			circle++
		
		}
	}

	result <- 4 * float64(circle) / float64(i)
}

func CalcPI(iter, processes int) float64 {
	var acc float64

	result := make(chan float64, processes)
	
	for i := 0; i < processes; i++ {
		go calcPartialPI(result, iter)
	}
	
	for i := 0; i < processes; i++ {
		acc += <-result
	}

	return acc / float64(processes)
}

func main() {
	iter := flag.Int("iter", 5000, "Iterations per process")
	processes := flag.Int("processes", 100, "Num of processes")

	flag.Parse()

	start := time.Nanoseconds()
	fmt.Printf("Approx PI value %f calculated in %f ms\n", 
		CalcPI(*iter, *processes),
		float(time.Nanoseconds() - start) / float(10e6))
}