G = 6.63784e-11
cm_to_m = 1. / 100.
msun_to_g = 1.988e33
pc_to_m = 3.08567758128e16
gcm_to_msunpc = 5.03e-34 * (3.086e18)**2
def print_log(time, gravity, particles, total_energy_at_t0):
kinetic_energy = gravity.kinetic_energy
potential_energy = gravity.potential_energy
total_energy_at_this_time = kinetic_energy + potential_energy
print "time : " , time
print "energy error : " , (total_energy_at_this_time - total_energy_at_t0) / total_energy_at_t0
def simulate_small_cluster(
number_of_stars = 1000.,
end_time = 40 | nbody_system.time,
number_of_workers = 1
):
#convert_nbody = nbody_system.nbody_to_si(number_of_stars | units.MSun, 1. | units.parsec)
f.close()
return
def gasvel_potential(sigma_cl, mstars, eps, k_rho, k_P=1., f_g=1., phi_Pc=4./3., phi_Pbar=1.32, R=None):
#R = 0.05 * np.power(A / (k_P**2 * eps**2 * phi_Pc * phi_Pbar), 1./4.) * np.power(np.sum(mstars) / 30., 1./2.) * sigma_cl**(-1./2.) * pc_to_m
if R is None:
R = clump_radius(mstars, sigma_cl, eps, k_rho, k_P, f_g, phi_Pc, phi_Pbar) * pc_to_m
#return G / (2. * (5. - 2. * k_rho)) / R * (np.sum(mstars) * msun_to_g / 1000.)**2
return - 3. / 5. * (1. - k_rho / 3.) / (1. - 2. * k_rho / 5.) * G * (np.sum(mstars) * msun_to_g / 1000.)**2. / R
def gasvel_ke(mstars, sigma_cl, eps, phi_b, k_rho, k_P=1., f_g=1., phi_Pc=4./3., phi_Pbar=1.32, R=None):
"""
Calculates the kinetic energy expected for a cluster with stars moving using a mass-averaged velocity dispersion.
mstars: array_like
Masses of the stars in solar masses
sigma: float
Mass-averaged velocity dispersion in km/s
"""
sigma = gasveldisp(mstars, sigma_cl, eps, phi_b, k_rho, k_P, f_g, phi_Pc, phi_Pbar)# * 7./6.
print(sigma)
#R = 0.05 * np.power(A / (k_P**2 * eps**2 * phi_Pc * phi_Pbar), 1./4.) * np.power(np.sum(mstars) / 30., 1./2.) * sigma_cl**(-1./2.)
if R is None:
R = clump_radius(mstars, sigma_cl, eps, k_rho, k_P, f_g, phi_Pc, phi_Pbar)
rho_s = (3. - k_rho) / (4. * np.pi) / R**3.
#print(sigma)
#print(rho_s)
#print(R_s)
return 3./2. * (np.sum(mstars) * msun_to_g / 1000.) * (sigma * 1000.)**2.
#return 2. * np.pi * (rho_s * np.sum(mstars) * msun_to_g / 1000) * (np.sqrt(3.) * sigma * 1000)**2. * R**3. / (5. - 2. * k_rho)
def radii(pos):
return np.sqrt((pos[ : , 0].value_in(units.parsec))**2 + (pos[ : , 1].value_in(units.parsec))**2 +(pos[ : , 2].value_in(units.parsec))**2)
def convert_to_nbody(mass, cluster):
"""
Converts a cluster to nbody units using the prescription of Heggie & Mathieu 1986
"""
Gun = G | units.m**3 * units.kg**-1. * units.s**-2.
mtot = np.sum(mass)
ke = cluster.kinetic_energy()
pe = cluster.potential_energy()
etot = ke + pe
if etot > 0 | units.m**2 * units.kg * units.s**-2:
etot *= -1.
subplot.scatter(
positions[...,0].value_in(nbody_system.length),
positions[...,1].value_in(nbody_system.length),
s = 1,
edgecolors = 'red',
facecolors = 'red'
)
subplot.set_xlim(-4.0,4.0)
subplot.set_ylim(-4.0,4.0)
subplot.set_aspect(1.)
title = 'time = {0:.2f}'.format(time.value_in(nbody_system.time))
subplot.set_title(title)#, fontsize=12)
spines = []
if index % plot_matrix_size == 0:
spines.append('left')
if index >= ((number_of_rows - 1)*plot_matrix_size):
spines.append('bottom')
adjust_spines(subplot, spines,np.arange(-4.0,4.1, 1.0))
if index % plot_matrix_size == 0:
subplot.set_ylabel('y')
if index >= ((number_of_rows - 1)*plot_matrix_size):
subplot.set_xlabel('x')
plt.savefig('simple_cluster_powerlaw.png', clobber=True)
def write_init_file(m, pos, vel, fname):
"""
Writes the initial masses, positions, and velocities of a cluster to a file.
"""
f = open(fname, 'w')
for i in np.arange(np.size(m)):
f.write(str(m[i]) + '\t' + str(pos[i,0]) + '\t' + str(pos[i,1]) + '\t' + str(pos[i,2]) + '\t' + str(vel[i,0]) + '\t' + '\t' + str(vel[i,1]) + '\t' + str(vel[i,2]) + '\n')
