Particle Data

We provide a flexible data structure to store data on a per-particle basis. The number of elements per particle and the data type are specified by the user.

Particle positions are stored in a particular type of ParticleDat called a PositionDat.

Standalone ParticleDat and PositionDat instances are not particularly useful as they do not automatically group the data for particles together. To group particle data please refer to the State Containers section.

ParticleDat Object

Particle properties are stored within ParticleDat containers. These can be considered as two dimensional matrices with each row storing data for a particle. For example the velocities of \(N\) particles would be stored within a \(N\) X \(3\) ParticleDat.

from ppmd import *
ParticleDat = data.ParticleDat
vel = ParticleDat(npart=N, ncomp=3)

ParticleDats may contain ctypes.c_double, ctypes.c_int and ctypes.c_long data. To specifiy a data type other than the default ctypes.c_double the dtype keyword should be used.

import ctypes
num_neighbours = ParticleDat(npart=N, ncomp=1, dtype=ctypes.c_int)

These data structures are specialised wrappers around Numpy objects and the underlying numpy data may be accessed by using the standard PythonNumpy indexing. For example to initialise the vel ParticleDat above with values drawn from a standard normal distribution we may do the following.

import numpy as np
vel[:,:] = np.random.normal(size=(N,3))

To create a CUDA ParticleDat use the ParticleDat from ppmd.cuda:

from ppmd.cuda import *
ParticleDat = cuda_data.ParticleDat
vel = ParticleDat(npart=N, ncomp=3)
vel[:,:] = np.random.normal(size=(N,3))

The code above creates a ParticleDat on a CUDA device and assigns the values drawn from a standard normal distribution. The copying of data between the host and the CUDA device is handled automatically by the framework.

PositionDat Object

PositionDats always have 3 components and are of type ctypes.c_double and can be initialised with

pos = PositionDat()