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'''
nbody sim
'''
from time import time
# Pulled from http://shootout.alioth.debian.org/u64q/benchmark.php?test=nbody&lang=python&id=4
# Contributed by Kevin Carson.
# Modified by Tupteq, Fredrik Johansson, and Daniel Nanz.
def main():
if PYTHON=='PYTHONJS':
pythonjs.configure( direct_operator='+' )
pythonjs.configure( direct_operator='*' )
pythonjs.configure( direct_keys=True )
pass
times = test_nbody( 3 )
avg = sum( times ) / 3.0
print( avg )
def combinations(l):
"""Pure-Python implementation of itertools.combinations(l, 2)."""
result = []
for x in range(len(l) - 1):
ls = l[x+1:]
for y in ls:
result.append((l[x],y))
return result
PI = 3.14159265358979323
SOLAR_MASS = 4 * PI * PI
DAYS_PER_YEAR = 365.24
BODIES = {
'sun': ([0.0, 0.0, 0.0], [0.0, 0.0, 0.0], SOLAR_MASS),
'jupiter': ([4.84143144246472090e+00,
-1.16032004402742839e+00,
-1.03622044471123109e-01],
[1.66007664274403694e-03 * DAYS_PER_YEAR,
7.69901118419740425e-03 * DAYS_PER_YEAR,
-6.90460016972063023e-05 * DAYS_PER_YEAR],
9.54791938424326609e-04 * SOLAR_MASS),
'saturn': ([8.34336671824457987e+00,
4.12479856412430479e+00,
-4.03523417114321381e-01],
[-2.76742510726862411e-03 * DAYS_PER_YEAR,
4.99852801234917238e-03 * DAYS_PER_YEAR,
2.30417297573763929e-05 * DAYS_PER_YEAR],
2.85885980666130812e-04 * SOLAR_MASS),
'uranus': ([1.28943695621391310e+01,
-1.51111514016986312e+01,
-2.23307578892655734e-01],
[2.96460137564761618e-03 * DAYS_PER_YEAR,
2.37847173959480950e-03 * DAYS_PER_YEAR,
-2.96589568540237556e-05 * DAYS_PER_YEAR],
4.36624404335156298e-05 * SOLAR_MASS),
'neptune': ([1.53796971148509165e+01,
-2.59193146099879641e+01,
1.79258772950371181e-01],
[2.68067772490389322e-03 * DAYS_PER_YEAR,
1.62824170038242295e-03 * DAYS_PER_YEAR,
-9.51592254519715870e-05 * DAYS_PER_YEAR],
5.15138902046611451e-05 * SOLAR_MASS) }
def advance(dt, n, bodies, pairs):
for i in range(n):
for pair in pairs:
p1,p2 = pair
vec1, v1, m1 = p1
vec2, v2, m2 = p2
x1, y1, z1 = vec1
x2, y2, z2 = vec2
dx = x1 - x2
dy = y1 - y2
dz = z1 - z2
mag = dt * ((dx * dx + dy * dy + dz * dz) ** (-1.5))
b1m = m1 * mag
b2m = m2 * mag
v1[0] -= dx * b2m
v1[1] -= dy * b2m
v1[2] -= dz * b2m
v2[0] += dx * b1m
v2[1] += dy * b1m
v2[2] += dz * b1m
for w in bodies:
r, v, m = w
r[0] += dt * v[0]
r[1] += dt * v[1]
r[2] += dt * v[2]
def report_energy(bodies, pairs):
e = 0.0
for pair in pairs:
p1,p2 = pair
vec1, v1, m1 = p1
vec2, v2, m2 = p2
x1, y1, z1 = vec1
x2, y2, z2 = vec2
dx = x1 - x2
dy = y1 - y2
dz = z1 - z2
e -= (m1 * m2) / ((dx * dx + dy * dy + dz * dz) ** 0.5)
for w in bodies:
r, v, m = w
vx, vy, vz = v
#e += m * (vx * vx + vy * vy + vz * vz) / 2.0 ## TODO fix this
a = vx * vx + vy * vy + vz * vz
a /= 2.0
e += m * a
return e
def offset_momentum(ref, bodies, px=0.0, py=0.0, pz=0.0):
for w in bodies:
r, v, m = w
vx, vy, vz = v
px -= vx * m
py -= vy * m
pz -= vz * m
(r, v, m) = ref
v[0] = px / m
v[1] = py / m
v[2] = pz / m
def test_nbody(iterations):
SYSTEM = []
for key in BODIES: SYSTEM.append( BODIES[key] )
PAIRS = combinations(SYSTEM)
times = []
for _ in range(iterations):
t0 = time()
start_e = report_energy( SYSTEM, PAIRS )
advance(0.01, 20000, SYSTEM, PAIRS)
end_e = report_energy( SYSTEM, PAIRS )
t1 = time()
print('#start energy:', start_e)
print('#end energy:', end_e)
times.append(t1 - t0)
return times