def new_particle_from_cluster_core(particles,
unit_converter=None,
density_weighting_power=2,
cm=None,
reuse_hop=False,
hop=HopContainer()):
"""
Uses Hop to find the density centre (core) of a particle distribution
and stores the properties of this core on a particle:
position, velocity, (core) radius and (core) density.
Particles are assigned weights that depend on the density (as determined by
Hop) to a certain power.
The default weighting power is 2, which is most commonly used. Set
density_weighting_power to 1 in order to get the original weighting of
Casertano & Hut (1985, ApJ, 298, 80).
:argument unit_converter: Required if the particles are in SI units
:argument density_weighting_power: Particle properties are weighted by density to this power
"""
if isinstance(hop, HopContainer):
hop.initialize(unit_converter)
hop = hop.code
in_hop = hop.particles.add_particles(particles)
hop.parameters.density_method = 2
hop.parameters.number_of_neighbors_for_local_density = 7
hop.calculate_densities()
density = in_hop.density.copy()
if not reuse_hop:
hop.stop()
weights = (density**density_weighting_power).reshape((-1, 1))
# Reshape makes sure that density can be multiplied with vectors, e.g. position
result = Particle()
result.density = density.amax()
total_weight = weights.sum()
if cm is None:
result.position = (weights *
particles.position).sum(axis=0) / total_weight
else:
result.position = cm
result.velocity = (weights * particles.velocity).sum(axis=0) / total_weight
result.radius = (
weights.flatten() *
(particles.position - result.position).lengths()).sum() / total_weight
return result
def new_particle_from_cluster_core(
particles, unit_converter=None, density_weighting_power=2, cm=None, reuse_hop=False, hop=HopContainer()
):
"""
Uses Hop to find the density centre (core) of a particle distribution
and stores the properties of this core on a particle:
position, velocity, (core) radius and (core) density.
Particles are assigned weights that depend on the density (as determined by
Hop) to a certain power.
The default weighting power is 2, which is most commonly used. Set
density_weighting_power to 1 in order to get the original weighting of
Casertano & Hut (1985, ApJ, 298, 80).
:argument unit_converter: Required if the particles are in SI units
:argument density_weighting_power: Particle properties are weighted by density to this power
"""
if isinstance(hop, HopContainer):
hop.initialize(unit_converter)
hop = hop.code
in_hop = hop.particles.add_particles(particles)
hop.parameters.density_method = 2
hop.parameters.number_of_neighbors_for_local_density = 7
hop.calculate_densities()
density = in_hop.density.copy()
if not reuse_hop:
hop.stop()
weights = (density ** density_weighting_power).reshape((-1, 1))
# Reshape makes sure that density can be multiplied with vectors, e.g. position
result = Particle()
result.density = density.amax()
total_weight = weights.sum()
if cm is None:
result.position = (weights * particles.position).sum(axis=0) / total_weight
else:
result.position = cm
result.velocity = (weights * particles.velocity).sum(axis=0) / total_weight
result.radius = (weights.flatten() * (particles.position - result.position).lengths()).sum() / total_weight
return result
