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diff --git a/benchmark/bm_so_nbody.rb b/benchmark/bm_so_nbody.rb
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+# The Computer Language Shootout
+# http://shootout.alioth.debian.org
+#
+# Optimized for Ruby by Jesse Millikan
+# From version ported by Michael Neumann from the C gcc version,
+# which was written by Christoph Bauer.
+
+SOLAR_MASS = 4 * Math::PI**2
+DAYS_PER_YEAR = 365.24
+
+def _puts *args
+end
+
+class Planet
+ attr_accessor :x, :y, :z, :vx, :vy, :vz, :mass
+
+ def initialize(x, y, z, vx, vy, vz, mass)
+ @x, @y, @z = x, y, z
+ @vx, @vy, @vz = vx * DAYS_PER_YEAR, vy * DAYS_PER_YEAR, vz * DAYS_PER_YEAR
+ @mass = mass * SOLAR_MASS
+ end
+
+ def move_from_i(bodies, nbodies, dt, i)
+ while i < nbodies
+ b2 = bodies[i]
+ dx = @x - b2.x
+ dy = @y - b2.y
+ dz = @z - b2.z
+
+ distance = Math.sqrt(dx * dx + dy * dy + dz * dz)
+ mag = dt / (distance * distance * distance)
+ b_mass_mag, b2_mass_mag = @mass * mag, b2.mass * mag
+
+ @vx -= dx * b2_mass_mag
+ @vy -= dy * b2_mass_mag
+ @vz -= dz * b2_mass_mag
+ b2.vx += dx * b_mass_mag
+ b2.vy += dy * b_mass_mag
+ b2.vz += dz * b_mass_mag
+ i += 1
+ end
+
+ @x += dt * @vx
+ @y += dt * @vy
+ @z += dt * @vz
+ end
+end
+
+def energy(bodies)
+ e = 0.0
+ nbodies = bodies.size
+
+ for i in 0 ... nbodies
+ b = bodies[i]
+ e += 0.5 * b.mass * (b.vx * b.vx + b.vy * b.vy + b.vz * b.vz)
+ for j in (i + 1) ... nbodies
+ b2 = bodies[j]
+ dx = b.x - b2.x
+ dy = b.y - b2.y
+ dz = b.z - b2.z
+ distance = Math.sqrt(dx * dx + dy * dy + dz * dz)
+ e -= (b.mass * b2.mass) / distance
+ end
+ end
+ e
+end
+
+def offset_momentum(bodies)
+ px, py, pz = 0.0, 0.0, 0.0
+
+ for b in bodies
+ m = b.mass
+ px += b.vx * m
+ py += b.vy * m
+ pz += b.vz * m
+ end
+
+ b = bodies[0]
+ b.vx = - px / SOLAR_MASS
+ b.vy = - py / SOLAR_MASS
+ b.vz = - pz / SOLAR_MASS
+end
+
+BODIES = [
+ # sun
+ Planet.new(0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1.0),
+
+ # jupiter
+ Planet.new(
+ 4.84143144246472090e+00,
+ -1.16032004402742839e+00,
+ -1.03622044471123109e-01,
+ 1.66007664274403694e-03,
+ 7.69901118419740425e-03,
+ -6.90460016972063023e-05,
+ 9.54791938424326609e-04),
+
+ # saturn
+ Planet.new(
+ 8.34336671824457987e+00,
+ 4.12479856412430479e+00,
+ -4.03523417114321381e-01,
+ -2.76742510726862411e-03,
+ 4.99852801234917238e-03,
+ 2.30417297573763929e-05,
+ 2.85885980666130812e-04),
+
+ # uranus
+ Planet.new(
+ 1.28943695621391310e+01,
+ -1.51111514016986312e+01,
+ -2.23307578892655734e-01,
+ 2.96460137564761618e-03,
+ 2.37847173959480950e-03,
+ -2.96589568540237556e-05,
+ 4.36624404335156298e-05),
+
+ # neptune
+ Planet.new(
+ 1.53796971148509165e+01,
+ -2.59193146099879641e+01,
+ 1.79258772950371181e-01,
+ 2.68067772490389322e-03,
+ 1.62824170038242295e-03,
+ -9.51592254519715870e-05,
+ 5.15138902046611451e-05)
+]
+
+init = 200_000 # ARGV[0]
+n = Integer(init)
+
+offset_momentum(BODIES)
+
+puts "%.9f" % energy(BODIES)
+
+nbodies = BODIES.size
+dt = 0.01
+
+n.times do
+ i = 0
+ while i < nbodies
+ b = BODIES[i]
+ b.move_from_i(BODIES, nbodies, dt, i + 1)
+ i += 1
+ end
+end
+
+puts "%.9f" % energy(BODIES)