Pi Using Numerical Integration: Go Language

Go is a new open-source language with built-in support for concurrency developed at Google. You may get more info on the language at http://golang.org/. In particular, here is an introduction into concurrency constructs: http://golang.org/doc/effective_go.html#concurrency. You can find the program in easily downloadable form here.

package main

import (
        "flag"
        "fmt"
        "math"
        "runtime"
)

var (
        nRect  = flag.Int("rect", 1e6, "number of rectangles")
        nGrain = flag.Int("grain", 1e4, "parallel task grain size (in rectangles)")
        nCPU   = flag.Int("cpu", 1, "number of CPUs to use")
)

func main() {
        flag.Parse()
        runtime.GOMAXPROCS(*nCPU)   // Set number of OS threads to use.
        nParts := 0                 // Number of parallel tasks.
        parts := make(chan float64) // Channel to collect part results.
        for i := 0; i < *nRect; i += *nGrain {
                nParts += 1
                end := i + *nGrain // Calculate end of this part.
                if end > *nRect {
                        end = *nRect
                }
                // Launch a concurrent goroutine to process this part.
                go func(begin, end int) {
                        sum := 0.0
                        h := 2.0 / float64(*nRect)
                        for i := begin; i < end; i++ {
                                x := -1 + (float64(i)+0.5)*h
                                sum += math.Sqrt(1-x*x) * h
                        }
                        parts <- sum // Send the result back.
                }(i, end)
        }

        // Aggregate part results.
        sum := 0.0
        for p := 0; p < nParts; p++ {
                sum += <-parts
        }
        pi := sum * 2.0
        fmt.Printf("PI = %g\n", pi)
}