Calculating Pi..

MonteCarloPi

package main

import (
	"fmt"
	"math"
	"math/rand"
	"time"
)

func calcPiRandom(nPoints int) float64 {
	rand.Seed(time.Now().UTC().UnixNano())

	// In- or outside of the circle.
	var nPointsInside int = 0
	var nPointsOutside int = 0

	for i := 0; i < nPoints; i++ {
		x, y := rand.Float64(), rand.Float64()
		if x*x+y*y < 1 {
			nPointsInside++
		} else {
			nPointsOutside++
		}
	}

	areaRatio := float64(nPointsInside) / float64(nPointsInside+nPointsOutside)

	// Note that areaRatio = (Pi*r^2) / (4*r^2)
	// So: 4 * areaRatio = Pi
	Pi := 4 * areaRatio

	return Pi
}

func calcPi(nPoints int) float64 {

	a := math.Sqrt(float64(nPoints))

	var stepSize float64 = 1.0 / a

	var nPointsInside int = 0
	var nPointsOutside int = 0

	for x := 0.0; x < 1; x += stepSize {
		for y := 0.0; y < 1; y += stepSize {
			if x*x+y*y < 1 {
				nPointsInside++
			} else {
				nPointsOutside++
			}
		}
	}

	areaRatio := float64(nPointsInside) / float64(nPointsInside+nPointsOutside)
	return 4 * areaRatio
}

func main() {

	fmt.Printf("Iteratively calculated Pi %f\n", calcPi(10000))
	fmt.Printf("Randomly calculated Pi %f\n", calcPiRandom(1000000))
}