The Computer Language
Benchmarks Game

n-body Java program

source code

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

   contributed by Mark C. Lewis
*/

import java.text.*;

public final class nbody {
   public static void main(String[] args) {      
      NumberFormat nf = NumberFormat.getInstance();
      nf.setMaximumFractionDigits(9);
      nf.setMinimumFractionDigits(9);
      nf.setGroupingUsed(false);      
   
      int n = Integer.parseInt(args[0]);
      
      NBodySystem bodies = new NBodySystem();
      
      System.out.println(nf.format(bodies.energy()) );
      for (int i=0; i<n; ++i) {
         bodies.advance(0.01);
      }
      System.out.println(nf.format(bodies.energy()) );      
   }
}


final class NBodySystem {      
   private Body[] bodies;
              
   public NBodySystem(){         
      bodies = new Body[]{
            Body.sun(),      
            Body.jupiter(),
            Body.saturn(),
            Body.uranus(),
            Body.neptune()                                    
         };
      
      double px = 0.0;
      double py = 0.0;   
      double pz = 0.0;            
      for(int i=0; i < bodies.length; ++i) {                                          
         px += bodies[i].vx * bodies[i].mass;
         py += bodies[i].vy * bodies[i].mass;      
         pz += bodies[i].vz * bodies[i].mass;            
      }      
      bodies[0].offsetMomentum(px,py,pz);
   }
                        
   public void advance(double dt) {
      double dx, dy, dz, distance, mag;   
   
      for(int i=0; i < bodies.length; ++i) {
         for(int j=i+1; j < bodies.length; ++j) {   
            dx = bodies[i].x - bodies[j].x;
            dy = bodies[i].y - bodies[j].y;
            dz = bodies[i].z - bodies[j].z;
            
            distance = Math.sqrt(dx*dx + dy*dy + dz*dz);               
            mag = dt / (distance * distance * distance);
            
            bodies[i].vx -= dx * bodies[j].mass * mag;
            bodies[i].vy -= dy * bodies[j].mass * mag;
            bodies[i].vz -= dz * bodies[j].mass * mag;
            
            bodies[j].vx += dx * bodies[i].mass * mag;
            bodies[j].vy += dy * bodies[i].mass * mag;
            bodies[j].vz += dz * bodies[i].mass * mag;
         }
      }      
      
      for(int i=0; i < bodies.length; ++i) {
         bodies[i].x += dt * bodies[i].vx;
         bodies[i].y += dt * bodies[i].vy;
         bodies[i].z += dt * bodies[i].vz;
      }      
   }         
   
   public double energy(){      
      double dx, dy, dz, distance;   
      double e = 0.0;         
      
      for (int i=0; i < bodies.length; ++i) {
         e += 0.5 * bodies[i].mass * 
            ( bodies[i].vx * bodies[i].vx 
            + bodies[i].vy * bodies[i].vy 
            + bodies[i].vz * bodies[i].vz );
            
         for (int j=i+1; j < bodies.length; ++j) {
            dx = bodies[i].x - bodies[j].x;
            dy = bodies[i].y - bodies[j].y;
            dz = bodies[i].z - bodies[j].z;
            
            distance = Math.sqrt(dx*dx + dy*dy + dz*dz);
            e -= (bodies[i].mass * bodies[j].mass) / distance;
         }
      }
      return e;
   }                                                                                                           
}


final class Body {
   static final double PI = 3.141592653589793;   
   static final double SOLAR_MASS = 4 * PI * PI;
   static final double DAYS_PER_YEAR = 365.24;

   public double x, y, z, vx, vy, vz, mass;
   
   public Body(){}   
   
   static Body jupiter(){
      Body p = new Body();
      p.x = 4.84143144246472090e+00;
      p.y = -1.16032004402742839e+00;
      p.z = -1.03622044471123109e-01;
      p.vx = 1.66007664274403694e-03 * DAYS_PER_YEAR;
      p.vy = 7.69901118419740425e-03 * DAYS_PER_YEAR;
      p.vz = -6.90460016972063023e-05 * DAYS_PER_YEAR;
      p.mass = 9.54791938424326609e-04 * SOLAR_MASS;                  
      return p;
   }   
   
   static Body saturn(){
      Body p = new Body();
      p.x = 8.34336671824457987e+00;
      p.y = 4.12479856412430479e+00;
      p.z = -4.03523417114321381e-01;
      p.vx = -2.76742510726862411e-03 * DAYS_PER_YEAR;
      p.vy = 4.99852801234917238e-03 * DAYS_PER_YEAR;
      p.vz = 2.30417297573763929e-05 * DAYS_PER_YEAR;
      p.mass = 2.85885980666130812e-04 * SOLAR_MASS;                  
      return p;
   }   
   
   static Body uranus(){
      Body p = new Body();
      p.x = 1.28943695621391310e+01;
      p.y = -1.51111514016986312e+01;
      p.z = -2.23307578892655734e-01;
      p.vx = 2.96460137564761618e-03 * DAYS_PER_YEAR;
      p.vy = 2.37847173959480950e-03 * DAYS_PER_YEAR;
      p.vz = -2.96589568540237556e-05 * DAYS_PER_YEAR;
      p.mass = 4.36624404335156298e-05 * SOLAR_MASS;                     
      return p;
   }      

   static Body neptune(){
      Body p = new Body();
      p.x = 1.53796971148509165e+01;
      p.y = -2.59193146099879641e+01;
      p.z = 1.79258772950371181e-01;
      p.vx = 2.68067772490389322e-03 * DAYS_PER_YEAR;
      p.vy = 1.62824170038242295e-03 * DAYS_PER_YEAR;
      p.vz = -9.51592254519715870e-05 * DAYS_PER_YEAR;
      p.mass = 5.15138902046611451e-05 * SOLAR_MASS;                  
      return p;
   }
   
   static Body sun(){
      Body p = new Body();
      p.mass = SOLAR_MASS;                  
      return p;
   }         
   
   Body offsetMomentum(double px, double py, double pz){
      vx = -px / SOLAR_MASS;
      vy = -py / SOLAR_MASS;
      vz = -pz / SOLAR_MASS;      
      return this;   
   }                             
}
    

notes, command-line, and program output

NOTES:
64-bit Ubuntu quad core
java 9.0.1
Java(TM) SE Runtime Environment (build 9.0.1+11)
Java HotSpot(TM) 64-Bit Server VM (build 9.0.1+11, mixed mode)


Wed, 25 Oct 2017 22:13:52 GMT

MAKE:
mv nbody.java nbody.java
mv: 'nbody.java' and 'nbody.java' are the same file
/home/dunham/benchmarksgame/nanobench/makefiles/u64q.programs.Makefile:337: recipe for target 'nbody.java_run' failed
make: [nbody.java_run] Error 1 (ignored)
/opt/src/jdk-9.0.1/bin/javac -d .  nbody.java

1.05s to complete and log all make actions

COMMAND LINE:
/opt/src/jdk-9.0.1/bin/java   nbody 50000000

PROGRAM OUTPUT:
-0.169075164
-0.169059907