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General simulation data file format.

Project description

GSD

The GSD file format is the native file format for HOOMD-blue. GSD files store trajectories of the HOOMD-blue system state in a binary file with efficient random access to frames. GSD allows all particle and topology properties to vary from one frame to the next. Use the GSD Python API to specify the initial condition for a HOOMD-blue simulation or analyze trajectory output with a script. Read a GSD trajectory with a visualization tool to explore the behavior of the simulation.

Resources

HOOMD examples

Create a hoomd gsd file.

>>> s = gsd.hoomd.Snapshot()
>>> s.particles.N = 4
>>> s.particles.types = ['A', 'B']
>>> s.particles.typeid = [0,0,1,1]
>>> s.particles.position = [[0,0,0],[1,1,1], [-1,-1,-1], [1,-1,-1]]
>>> s.configuration.box = [3, 3, 3, 0, 0, 0]
>>> traj = gsd.hoomd.open(name='test.gsd', mode='wb')
>>> traj.append(s)

Append frames to a gsd file:

>>> def create_frame(i):
...     s = gsd.hoomd.Snapshot();
...     s.configuration.step = i;
...     s.particles.N = 4+i;
...     s.particles.position = numpy.random.random(size=(4+i,3))
...     return s;
>>> with gsd.hoomd.open('test.gsd', 'ab') as t:
...     t.extend( (create_frame(i) for i in range(10)) )
...     print(len(t))
11

Randomly index frames:

>>> with gsd.hoomd.open('test.gsd', 'rb') as t:
...     snap = t[5]
...     print(snap.configuration.step)
4
...     print(snap.particles.N)
8
...     print(snap.particles.position)
[[ 0.56993282  0.42243481  0.5502916 ]
 [ 0.36892486  0.38167036  0.27310368]
 [ 0.04739023  0.13603486  0.196539  ]
 [ 0.120232    0.91591144  0.99463677]
 [ 0.79806316  0.16991436  0.15228257]
 [ 0.13724308  0.14253527  0.02505   ]
 [ 0.39287439  0.82519054  0.01613089]
 [ 0.23150323  0.95167434  0.7715748 ]]

Slice frames:

>>> with gsd.hoomd.open('test.gsd', 'rb') as t:
...     for s in t[5:-2]:
...         print(s.configuration.step, end=' ')
4 5 6 7

File layer examples

with gsd.fl.open(name='file.gsd', mode='wb') as f:
    f.write_chunk(name='position', data=numpy.array([[1,2,3],[4,5,6]], dtype=numpy.float32));
    f.write_chunk(name='angle', data=numpy.array([0, 1], dtype=numpy.float32));
    f.write_chunk(name='box', data=numpy.array([10, 10, 10], dtype=numpy.float32));
    f.end_frame()
with gsd.fl.open(name='file.gsd', mode='rb') as f:
    for i in range(1,f.nframes):
        position = f.read_chunk(frame=i, name='position');
        do_something(position);

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