source code
/* The Computer Language Benchmarks Game
http://benchmarksgame.alioth.debian.org/
contributed by Albert Sidelnik and Brad Chamberlain
derived from the Java version by Mark C. Lewis and Chad Whipkey
*/
config const n = 10000; // The number of timesteps to simulate
const pi = 3.141592653589793,
solarMass = 4 * pi**2,
daysPerYear = 365.24;
//
// a record for representing the position, velocity, and mass of
// bodies in the solar system
//
record body {
var pos: 3*real;
var vel: 3*real;
var mass: real;
}
//
// the array of bodies that we'll be simulating
//
var bodies = [/* sun */
new body(mass = solarMass),
/* jupiter */
new body(pos = ( 4.84143144246472090e+00,
-1.16032004402742839e+00,
-1.03622044471123109e-01),
vel = ( 1.66007664274403694e-03 * daysPerYear,
7.69901118419740425e-03 * daysPerYear,
-6.90460016972063023e-05 * daysPerYear),
mass = 9.54791938424326609e-04 * solarMass),
/* saturn */
new body(pos = ( 8.34336671824457987e+00,
4.12479856412430479e+00,
-4.03523417114321381e-01),
vel = (-2.76742510726862411e-03 * daysPerYear,
4.99852801234917238e-03 * daysPerYear,
2.30417297573763929e-05 * daysPerYear),
mass = 2.85885980666130812e-04 * solarMass),
/* uranus */
new body(pos = ( 1.28943695621391310e+01,
-1.51111514016986312e+01,
-2.23307578892655734e-01),
vel = ( 2.96460137564761618e-03 * daysPerYear,
2.37847173959480950e-03 * daysPerYear,
-2.96589568540237556e-05 * daysPerYear),
mass = 4.36624404335156298e-05 * solarMass),
/* neptune */
new body(pos = ( 1.53796971148509165e+01,
-2.59193146099879641e+01,
1.79258772950371181e-01),
vel = ( 2.68067772490389322e-03 * daysPerYear,
1.62824170038242295e-03 * daysPerYear,
-9.51592254519715870e-05 * daysPerYear),
mass = 5.15138902046611451e-05 * solarMass)
];
const numBodies = bodies.size; // the number of bodies being simulated
proc main() {
initSun(); // initialize the sun's velocity
writef("%.9r\n", energy()); // print the initial energy
for 1..n do // simulate 'n' timesteps
advance(0.01);
writef("%.9r\n", energy()); // print the final energy
}
//
// compute the sun's initial velocity
//
proc initSun() {
const p = + reduce (for b in bodies do (b.vel * b.mass));
bodies[1].vel = -p / solarMass;
}
//
// advance the positions and velocities of all the bodies
//
proc advance(dt) {
for i in 1..numBodies {
for j in i+1..numBodies {
ref b1 = bodies[i],
b2 = bodies[j];
const dpos = b1.pos - b2.pos,
mag = dt / sqrt(sumOfSquares(dpos))**3;
b1.vel -= dpos * b2.mass * mag;
b2.vel += dpos * b1.mass * mag;
}
}
for b in bodies do
b.pos += dt * b.vel;
}
//
// compute the energy of the bodies
//
proc energy() {
var e = 0.0;
for i in 1..numBodies {
const b1 = bodies[i];
e += 0.5 * b1.mass * sumOfSquares(b1.vel);
for j in i+1..numBodies {
const b2 = bodies[j];
e -= (b1.mass * b2.mass) / sqrt(sumOfSquares(b1.pos - b2.pos));
}
}
return e;
}
//
// compute the sum of squares of a 3-tuple's elements
//
inline proc sumOfSquares(x) {
return x(1)**2 + x(2)**2 + x(3)**2;
}