Source code for MDAnalysis.analysis.distances

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Distance analysis --- :mod:`MDAnalysis.analysis.distances`

This module provides functions to rapidly compute distances between
atoms or groups of atoms.

:func:`dist` and :func:`between` can take atom groups that do not even
have to be from the same :class:`~MDAnalysis.core.universe.Universe`.

See Also

__all__ = ['distance_array', 'self_distance_array',
           'contact_matrix', 'dist', 'between']

import numpy as np
import scipy.sparse

from MDAnalysis.lib.distances import (
           self_distance_array, distance_array,  # legacy reasons
from MDAnalysis.lib.c_distances import contact_matrix_no_pbc, contact_matrix_pbc
from MDAnalysis.lib.NeighborSearch import AtomNeighborSearch
from MDAnalysis.lib.distances import calc_bonds

import warnings
import logging
logger = logging.getLogger("MDAnalysis.analysis.distances")

[docs]def contact_matrix(coord, cutoff=15.0, returntype="numpy", box=None): '''Calculates a matrix of contacts. There is a fast, high-memory-usage version for small systems (*returntype* = 'numpy'), and a slower, low-memory-usage version for larger systems (*returntype* = 'sparse'). If *box* dimensions are passed then periodic boundary conditions are applied. Parameters --------- coord : array Array of coordinates of shape ``(N, 3)`` and dtype float32. cutoff : float, optional, default 15 Particles within `cutoff` are considered to form a contact. returntype : string, optional, default "numpy" Select how the contact matrix is returned. * ``"numpy"``: return as an ``(N. N)`` :class:`numpy.ndarray` * ``"sparse"``: return as a :class:`scipy.sparse.lil_matrix` 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. Returns ------- array or sparse matrix The contact matrix is returned in a format determined by the `returntype` keyword. See Also -------- :mod:`MDAnalysis.analysis.contacts` for native contact analysis .. versionchanged:: 0.11.0 Keyword *suppress_progmet* and *progress_meter_freq* were removed. ''' if returntype == "numpy": adj = np.full((len(coord), len(coord)), False, dtype=bool) pairs = capped_distance(coord, coord, max_cutoff=cutoff, box=box, return_distances=False) idx, idy = np.transpose(pairs) adj[idx, idy]=True return adj elif returntype == "sparse": # Initialize square List of Lists matrix of dimensions equal to number # of coordinates passed sparse_contacts = scipy.sparse.lil_matrix((len(coord), len(coord)), dtype='bool') if box is not None: # with PBC contact_matrix_pbc(coord, sparse_contacts, box, cutoff) else: # without PBC contact_matrix_no_pbc(coord, sparse_contacts, cutoff) return sparse_contacts
[docs]def dist(A, B, offset=0, box=None): """Return distance between atoms in two atom groups. The distance is calculated atom-wise. The residue ids are also returned because a typical use case is to look at CA distances before and after an alignment. Using the `offset` keyword one can also add a constant offset to the resids which facilitates comparison with PDB numbering. Arguments --------- A, B : AtomGroup :class:`~MDAnalysis.core.groups.AtomGroup` with the same number of atoms offset : integer or tuple, optional, default 0 An integer `offset` is added to *resids_A* and *resids_B* (see below) in order to produce PDB numbers. If `offset` is :class:`tuple` then ``offset[0]`` is added to *resids_A* and ``offset[1]`` to *resids_B*. Note that one can actually supply numpy arrays of the same length as the atom group so that an individual offset is added to each resid. Returns ------- resids_A : array residue ids of the `A` group (possibly changed with `offset`) resids_B : array residue ids of the `B` group (possibly changed with `offset`) distances : array distances between the atoms """ if A.atoms.n_atoms != B.atoms.n_atoms: raise ValueError("AtomGroups A and B do not have the same number of atoms") try: off_A, off_B = offset except (TypeError, ValueError): off_A = off_B = int(offset) residues_A = np.array(A.resids) + off_A residues_B = np.array(B.resids) + off_B d = calc_bonds(A.positions, B.positions, box) return np.array([residues_A, residues_B, d])
[docs]def between(group, A, B, distance): """Return sub group of `group` that is within `distance` of both `A` and `B` This function is not aware of periodic boundary conditions. Can be used to find bridging waters or molecules in an interface. Similar to "*group* and (AROUND *A* *distance* and AROUND *B* *distance*)". Parameters ---------- group : AtomGroup Find members of `group` that are between `A` and `B` A : AtomGroup B : AtomGroup `A` and `B` are the groups of atoms between which atoms in `group` are searched for. The function works is more efficient if `group` is bigger than either `A` or `B`. distance : float maximum distance for an atom to be counted as in the vicinity of `A` or `B` Returns ------- AtomGroup :class:`~MDAnalysis.core.groups.AtomGroup` of atoms that fulfill the criterion .. versionadded: 0.7.5 """ ns_group = AtomNeighborSearch(group) resA = set(, distance)) resB = set(, distance)) return sum(sorted(resB.intersection(resA)))