Source code for MDAnalysis.lib.pkdtree
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"""
PeriodicKDTree --- :mod:`MDAnalysis.lib.pkdtree`
================================================
This module contains a class to allow searches on a KDTree involving periodic
boundary conditions.
"""
import itertools
import numpy as np
from scipy.spatial import cKDTree
from ._cutil import unique_int_1d
from ._augment import augment_coordinates, undo_augment
from .util import unique_rows
from MDAnalysis.lib.distances import apply_PBC
__all__ = [
'PeriodicKDTree'
]
[docs]class PeriodicKDTree(object):
"""Wrapper around :class:`scipy.spatial.cKDTree`
Creates an object which can handle periodic as well as
non periodic boundary condtions depending on the parameters
provided while constructing the tree.
To enable periodic boundary conditions, box dimensions must be
provided. Periodic Boundary conditions are implemented by creating
duplicates of the particles which are within the specified cutoff
distance from the boundary. These duplicates along with the
original particle coordinates are used with the cKDTree without
any special treatment due to PBC beyond this point. The final
results after any operation with duplicate particle indices can be
traced back to the original particle using the
:func:`MDAnalysis.lib.distances.undo_augment` function.
"""
def __init__(self, box=None, leafsize=10):
"""
Parameters
----------
box : array-like or ``None``, optional, default ``None``
Simulation cell dimensions in the form of
:attr:`MDAnalysis.trajectory.base.Timestep.dimensions` when
periodic boundary conditions should be taken into account for
the calculation of contacts.
leafsize : int (optional)
Number of entries in leafs of the KDTree. If you suffer poor
performance you can play around with this number. Increasing the
`leafsize` will speed up the construction of the KDTree but
slow down the search.
"""
self.leafsize = leafsize
self.dim = 3 # 3D systems
self.box = box
self._built = False
self.cutoff = None
@property
def pbc(self):
"""Flag to indicate the presence of periodic boundaries.
- ``True`` if PBC are taken into account
- ``False`` if no unitcell dimension is available.
This is a managed attribute and can only be read.
"""
return self.box is not None
[docs] def set_coords(self, coords, cutoff=None):
"""Constructs KDTree from the coordinates
Wrapping of coordinates to the primary unit cell is enforced
before any distance evaluations. If periodic boundary conditions
are enabled, then duplicate particles are generated in the
vicinity of the box. An additional array `mapping` is also
generated which can be later used to trace the origin of
duplicate particle coordinates.
For non-periodic calculations, cutoff should not be provided
the parameter is only required for periodic calculations.
Parameters
----------
coords: array_like
Coordinate array of shape ``(N, 3)`` for N atoms.
cutoff: float
Specified cutoff distance to create duplicate images
Typically equivalent to the desired search radius
or the maximum of the desired cutoff radius. Relevant images
corresponding to every atom which lies
within ``cutoff`` distance from either of the box boundary
will be generated.
See Also
--------
MDAnalysis.lib.distances.augment_coordinates
"""
# If no cutoff distance is provided but PBC aware
if self.pbc and (cutoff is None):
raise RuntimeError('Provide a cutoff distance'
' with tree.set_coords(...)')
# set coords dtype to float32
# augment coordinates will work only with float32
coords = np.asarray(coords, dtype=np.float32)
if self.pbc:
self.cutoff = cutoff
# Bring the coordinates in the central cell
self.coords = apply_PBC(coords, self.box)
# generate duplicate images
self.aug, self.mapping = augment_coordinates(self.coords,
self.box,
self.cutoff)
# Images + coords
self.all_coords = np.concatenate([self.coords, self.aug])
self.ckdt = cKDTree(self.all_coords, leafsize=self.leafsize)
else:
# if cutoff distance is provided for non PBC calculations
if cutoff is not None:
raise RuntimeError('Donot provide cutoff distance for'
' non PBC aware calculations')
self.coords = coords
self.ckdt = cKDTree(self.coords, self.leafsize)
self._built = True
[docs] def search(self, centers, radius):
"""Search all points within radius from centers and their periodic images.
All the centers coordinates are wrapped around the central cell
to enable distance evaluations from points in the tree
and their images.
Parameters
----------
centers: array_like (N,3)
coordinate array to search for neighbors
radius: float
maximum distance to search for neighbors.
"""
if not self._built:
raise RuntimeError('Unbuilt tree. Run tree.set_coords(...)')
centers = np.asarray(centers)
if centers.shape == (self.dim, ):
centers = centers.reshape((1, self.dim))
# Sanity check
if self.pbc:
if self.cutoff < radius:
raise RuntimeError('Set cutoff greater or equal to the radius.')
# Bring all query points to the central cell
wrapped_centers = apply_PBC(centers, self.box)
indices = list(self.ckdt.query_ball_point(wrapped_centers,
radius))
self._indices = np.array(list(
itertools.chain.from_iterable(indices)),
dtype=np.intp)
if self._indices.size > 0:
self._indices = undo_augment(self._indices,
self.mapping,
len(self.coords))
else:
wrapped_centers = np.asarray(centers)
indices = list(self.ckdt.query_ball_point(wrapped_centers,
radius))
self._indices = np.array(list(
itertools.chain.from_iterable(indices)),
dtype=np.intp)
self._indices = np.asarray(unique_int_1d(self._indices))
return self._indices
[docs] def get_indices(self):
"""Return the neighbors from the last query.
Returns
------
indices : list
neighbors for the last query points and search radius
"""
return self._indices
[docs] def search_pairs(self, radius):
"""Search all the pairs within a specified radius
Parameters
----------
radius : float
Maximum distance between pairs of coordinates
Returns
-------
pairs : array
Indices of all the pairs which are within the specified radius
"""
if not self._built:
raise RuntimeError(' Unbuilt Tree. Run tree.set_coords(...)')
if self.pbc:
if self.cutoff < radius:
raise RuntimeError('Set cutoff greater or equal to the radius.')
pairs = np.array(list(self.ckdt.query_pairs(radius)), dtype=np.intp)
if self.pbc:
if len(pairs) > 1:
pairs[:, 0] = undo_augment(pairs[:, 0], self.mapping,
len(self.coords))
pairs[:, 1] = undo_augment(pairs[:, 1], self.mapping,
len(self.coords))
if pairs.size > 0:
# First sort the pairs then pick the unique pairs
pairs = np.sort(pairs, axis=1)
pairs = unique_rows(pairs)
return pairs
[docs] def search_tree(self, centers, radius):
"""
Searches all the pairs within `radius` between `centers`
and ``coords``
``coords`` are the already initialized coordinates in the tree
during :meth:`set_coords`.
``centers`` are wrapped around the primary unit cell
if PBC is desired. Minimum image convention (PBC) is
activated if the `box` argument is provided during
class initialization
Parameters
----------
centers: array_like (N,3)
coordinate array to search for neighbors
radius: float
maximum distance to search for neighbors.
Returns
-------
pairs : array
all the pairs between ``coords`` and ``centers``
Note
----
This method constructs another tree from the ``centers``
and queries the previously built tree (built in
:meth:`set_coords`)
"""
if not self._built:
raise RuntimeError('Unbuilt tree. Run tree.set_coords(...)')
centers = np.asarray(centers)
if centers.shape == (self.dim, ):
centers = centers.reshape((1, self.dim))
# Sanity check
if self.pbc:
if self.cutoff < radius:
raise RuntimeError('Set cutoff greater or equal to the radius.')
# Bring all query points to the central cell
wrapped_centers = apply_PBC(centers, self.box)
other_tree = cKDTree(wrapped_centers, leafsize=self.leafsize)
pairs = other_tree.query_ball_tree(self.ckdt, radius)
pairs = np.array([[i, j] for i, lst in enumerate(pairs) for j in lst],
dtype=np.intp)
if pairs.size > 0:
pairs[:, 1] = undo_augment(pairs[:, 1],
self.mapping,
len(self.coords))
else:
other_tree = cKDTree(centers, leafsize=self.leafsize)
pairs = other_tree.query_ball_tree(self.ckdt, radius)
pairs = np.array([[i, j] for i, lst in enumerate(pairs) for j in lst],
dtype=np.intp)
if pairs.size > 0:
pairs = unique_rows(pairs)
return pairs