function test()
{
$pi = 3.141592653589793;
$solar_mass = 4 * $pi * $pi;
$days_per_year = 365.24;
$bodies = array(array(0.0, 0.0, 0.0, 0.0, 0.0, 0.0, $solar_mass), array(4.841431442464721, -1.1603200440274284, -0.10362204447112311, 0.001660076642744037 * $days_per_year, 0.007699011184197404 * $days_per_year, -6.90460016972063E-5 * $days_per_year, 0.0009547919384243266 * $solar_mass), array(8.34336671824458, 4.124798564124305, -0.4035234171143214, -0.002767425107268624 * $days_per_year, 0.004998528012349172 * $days_per_year, 2.3041729757376393E-5 * $days_per_year, 0.0002858859806661308 * $solar_mass), array(12.894369562139131, -15.111151401698631, -0.22330757889265573, 0.002964601375647616 * $days_per_year, 0.0023784717395948095 * $days_per_year, -2.9658956854023756E-5 * $days_per_year, 4.366244043351563E-5 * $solar_mass), array(15.379697114850917, -25.919314609987964, 0.17925877295037118, 0.0026806777249038932 * $days_per_year, 0.001628241700382423 * $days_per_year, -9.515922545197159E-5 * $days_per_year, 5.1513890204661145E-5 * $solar_mass));
// offset_momentum
$px = $py = $pz = 0.0;
foreach ($bodies as &$e) {
$px += $e[3] * $e[6];
$py += $e[4] * $e[6];
$pz += $e[5] * $e[6];
}
$bodies[0][3] = -$px / $solar_mass;
$bodies[0][4] = -$py / $solar_mass;
$bodies[0][5] = -$pz / $solar_mass;
$pairs = array();
for ($i = 0, $m = count($bodies); $i < $m; $i++) {
for ($j = $i + 1; $j < $m; $j++) {
$pairs[] = array(&$bodies[$i], &$bodies[$j]);
}
}
$n = 2;
// printf("%0.9f\n", energy($bodies));
$i = 0;
do {
foreach ($pairs as &$p) {
$a =& $p[0];
$b =& $p[1];
$dx = $a[0] - $b[0];
$dy = $a[1] - $b[1];
$dz = $a[2] - $b[2];
$dist = sqrt($dx * $dx + $dy * $dy + $dz * $dz);
$mag = 0.01 / ($dist * $dist * $dist);
$mag_a = $a[6] * $mag;
$mag_b = $b[6] * $mag;
$a[3] -= $dx * $mag_b;
$a[4] -= $dy * $mag_b;
$a[5] -= $dz * $mag_b;
$b[3] += $dx * $mag_a;
$b[4] += $dy * $mag_a;
$b[5] += $dz * $mag_a;
}
foreach ($bodies as &$b) {
$b[0] += 0.01 * $b[3];
$b[1] += 0.01 * $b[4];
$b[2] += 0.01 * $b[5];
}
} while (++$i < $n);
return energy($bodies);
}
}
}
$n = $argv[1];
printf("%0.9f\n", energy($bodies));
$i = 0;
do {
foreach ($pairs as &$p) {
$a =& $p[0];
$b =& $p[1];
$dx = $a[0] - $b[0];
$dy = $a[1] - $b[1];
$dz = $a[2] - $b[2];
$dist = sqrt($dx * $dx + $dy * $dy + $dz * $dz);
$mag = 0.01 / ($dist * $dist * $dist);
$mag_a = $a[6] * $mag;
$mag_b = $b[6] * $mag;
$a[3] -= $dx * $mag_b;
$a[4] -= $dy * $mag_b;
$a[5] -= $dz * $mag_b;
$b[3] += $dx * $mag_a;
$b[4] += $dy * $mag_a;
$b[5] += $dz * $mag_a;
}
foreach ($bodies as &$b) {
$b[0] += 0.01 * $b[3];
$b[1] += 0.01 * $b[4];
$b[2] += 0.01 * $b[5];
}
} while (++$i < $n);
printf("%0.9f\n", energy($bodies));
