Source code for MDAnalysis.transformations.wrap

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"""\
Wrap/unwrap transformations --- :mod:`MDAnalysis.transformations.wrap`
======================================================================

Wrap/unwrap the atoms of a given AtomGroup in the unit cell. :func:`wrap` 
translates the atoms back in the unit cell. :func:`unwrap` translates the
atoms of each molecule so that bons don't split over images.

.. autofunction:: wrap

.. autofunction:: unwrap

"""

from __future__ import absolute_import

from ..lib._cutil import make_whole

[docs]def wrap(ag, compound='atoms'): """ Shift the contents of a given AtomGroup back into the unit cell. :: +-----------+ +-----------+ | | | | | 3 | 6 | 6 3 | | ! | ! | ! ! | | 1-2-|-5-8 -> |-5-8 1-2-| | ! | ! | ! ! | | 4 | 7 | 7 4 | | | | | +-----------+ +-----------+ Example ------- .. code-block:: python ag = u.atoms transform = mda.transformations.wrap(ag) u.trajectory.add_transformations(transform) Parameters ---------- ag: Atomgroup Atomgroup to be wrapped in the unit cell compound : {'atoms', 'group', 'residues', 'segments', 'fragments'}, optional The group which will be kept together through the shifting process. Notes ----- When specifying a `compound`, the translation is calculated based on each compound. The same translation is applied to all atoms within this compound, meaning it will not be broken by the shift. This might however mean that not all atoms from the compound are inside the unit cell, but rather the center of the compound is. Returns ------- MDAnalysis.coordinates.base.Timestep """ def wrapped(ts): ag.wrap(compound=compound) return ts return wrapped
[docs]def unwrap(ag): """ Move all atoms in an AtomGroup so that bonds don't split over images Atom positions are modified in place. This function is most useful when atoms have been packed into the primary unit cell, causing breaks mid molecule, with the molecule then appearing on either side of the unit cell. This is problematic for operations such as calculating the center of mass of the molecule. :: +-----------+ +-----------+ | | | | | 6 3 | | 3 | 6 | ! ! | | ! | ! |-5-8 1-2-| -> | 1-2-|-5-8 | ! ! | | ! | ! | 7 4 | | 4 | 7 | | | | +-----------+ +-----------+ Example ------- .. code-block:: python ag = u.atoms transform = mda.transformations.unwrap(ag) u.trajectory.add_transformations(transform) Parameters ---------- atomgroup : AtomGroup The :class:`MDAnalysis.core.groups.AtomGroup` to work with. The positions of this are modified in place. Returns ------- MDAnalysis.coordinates.base.Timestep """ try: ag.fragments except AttributeError: raise AttributeError("{} has no fragments".format(ag)) def wrapped(ts): for frag in ag.fragments: make_whole(frag) return ts return wrapped