The Computer Language
Benchmarks Game

n-body C# .NET Core #5 program

source code

/* The Computer Language Benchmarks Game
   http://benchmarksgame.alioth.debian.org/

   contributed by Isaac Gouy, optimization and use of more C# idioms by Robert F. Tobler
   small optimisations by Anthony Lloyd
*/

using System;
using System.Runtime.CompilerServices;

class Body { public double x, y, z, vx, vy, vz, mass; }
class Pair { public Body bi, bj; }

public static class NBody
{
    const double dt = 0.01;
    
    static Body[] createBodies()
    {
        const double Pi = 3.141592653589793;
        const double Solarmass = 4 * Pi * Pi;
        const double DaysPeryear = 365.24;
        var jupiter = new Body {
                x = 4.84143144246472090e+00,
                y = -1.16032004402742839e+00,
                z = -1.03622044471123109e-01,
                vx = 1.66007664274403694e-03 * DaysPeryear,
                vy = 7.69901118419740425e-03 * DaysPeryear,
                vz = -6.90460016972063023e-05 * DaysPeryear,
                mass = 9.54791938424326609e-04 * Solarmass,
            };
        var saturn = new Body {
                x = 8.34336671824457987e+00,
                y = 4.12479856412430479e+00,
                z = -4.03523417114321381e-01,
                vx = -2.76742510726862411e-03 * DaysPeryear,
                vy = 4.99852801234917238e-03 * DaysPeryear,
                vz = 2.30417297573763929e-05 * DaysPeryear,
                mass = 2.85885980666130812e-04 * Solarmass,
            };
        var uranus = new Body {
                x = 1.28943695621391310e+01,
                y = -1.51111514016986312e+01,
                z = -2.23307578892655734e-01,
                vx = 2.96460137564761618e-03 * DaysPeryear,
                vy = 2.37847173959480950e-03 * DaysPeryear,
                vz = -2.96589568540237556e-05 * DaysPeryear,
                mass = 4.36624404335156298e-05 * Solarmass,
            };
        var neptune = new Body {
                x = 1.53796971148509165e+01,
                y = -2.59193146099879641e+01,
                z = 1.79258772950371181e-01,
                vx = 2.68067772490389322e-03 * DaysPeryear,
                vy = 1.62824170038242295e-03 * DaysPeryear,
                vz = -9.51592254519715870e-05 * DaysPeryear,
                mass = 5.15138902046611451e-05 * Solarmass,
            };
        var sun = new Body {
                mass = Solarmass,
                vx = (jupiter.vx * jupiter.mass + saturn.vx * saturn.mass
                        +uranus.vx * uranus.mass + neptune.vx * neptune.mass)/-Solarmass,
                vy = (jupiter.vy * jupiter.mass + saturn.vy * saturn.mass
                        +uranus.vy * uranus.mass + neptune.vy * neptune.mass)/-Solarmass,
                vz = (jupiter.vz * jupiter.mass + saturn.vz * saturn.mass
                        +uranus.vz * uranus.mass + neptune.vz * neptune.mass)/-Solarmass,
            };
        return new Body[] {sun, jupiter, saturn, uranus, neptune};
    }

    static Pair[] createPairs(Body[] bodies)
    {
        var pairs = new Pair[bodies.Length * (bodies.Length-1)/2];        
        int pi = 0;
        for (int i = 0; i < bodies.Length-1; i++)
        {
            var bi = bodies[i];
            for (int j = i+1; j < bodies.Length; j++)
                pairs[pi++] = new Pair() { bi = bi, bj = bodies[j] };
        }
        return pairs;
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    static double energy(Body[] bodies)
    {
        double e = 0.0;
        foreach (var b in bodies)
        {
            e += b.mass * (b.vx*b.vx + b.vy*b.vy + b.vz*b.vz);
        }
        e *= 0.5;
        for(int i=0; i<bodies.Length-1; ++i)
        {
            var bi = bodies[i];
            double ix = bi.x, iy = bi.y, iz = bi.z, imass = bi.mass;
            for(int j=i+1; j<bodies.Length; ++j)
            {
                var bj = bodies[j];
                double dx = ix - bj.x, dy = iy - bj.y, dz = iz - bj.z;
                e -= imass * bj.mass / Math.Sqrt(dx * dx + dy * dy + dz * dz);
            }
        }
        return e;
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    static void advance(Pair[] pairs, Body[] bodies)
    {
        foreach (var p in pairs)
        {
            Body bi = p.bi, bj = p.bj;
            double dx = bj.x - bi.x, dy = bj.y - bi.y, dz = bj.z - bi.z;
            double d2 = dx * dx + dy * dy + dz * dz;
            double mag = dt / (d2 * Math.Sqrt(d2));
            bi.vx += dx * bj.mass * mag; bj.vx -= dx * bi.mass * mag;
            bi.vy += dy * bj.mass * mag; bj.vy -= dy * bi.mass * mag;
            bi.vz += dz * bj.mass * mag; bj.vz -= dz * bi.mass * mag;
        }
        foreach (var b in bodies)
        {
            b.x += dt * b.vx; b.y += dt * b.vy; b.z += dt * b.vz;
        }
    }

    public static void Main(String[] args)
    {
        var bodies = createBodies();
        Console.Out.WriteLineAsync(energy(bodies).ToString("F9"));
        var pairs = createPairs(bodies);
        var before = Math.Round(energy(bodies),10);
        int n = args.Length > 0 ? Int32.Parse(args[0]) : 10000;
        while(n-->0) advance(pairs, bodies);
        Console.Out.WriteLineAsync(energy(bodies).ToString("F9"));
    }
}
    

notes, command-line, and program output

NOTES:
64-bit Ubuntu quad core
2.0.0 cdcd1928c9
"System.GC.Server": true


Mon, 14 Aug 2017 20:16:36 GMT

MAKE:
cp nbody.csharpcore-5.csharpcore Program.cs
cp Include/csharpcore/tmp.csproj .
cp Include/csharpcore/runtimeconfig.template.json .
mkdir obj
cp Include/csharpcore/tmp.csproj.nuget.g.props ./obj
cp Include/csharpcore/tmp.csproj.nuget.g.targets ./obj
/usr/bin/dotnet build -c Release
Microsoft (R) Build Engine version 15.3.409.57025 for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

  tmp -> /home/dunham/benchmarksgame_quadcore/nbody/tmp/bin/Release/netcoreapp2.0/tmp.dll

Build succeeded.
    0 Warning(s)
    0 Error(s)

Time Elapsed 00:00:03.50

6.11s to complete and log all make actions

COMMAND LINE:
/usr/bin/dotnet ./bin/Release/netcoreapp2.0/tmp.dll 50000000

PROGRAM OUTPUT:
-0.169075164
-0.169059907