6.8. GRO file format — MDAnalysis.coordinates.GRO
Classes to read and write Gromacs GRO coordinate files; see the notes on the GRO format which includes a conversion routine for the box.
6.8.1. Writing GRO files
By default any written GRO files will renumber the atom ids to move sequentially from 1. This can be disabled, and instead the original atom ids kept, by using the reindex=False keyword argument. This is useful when writing a subsection of a larger Universe while wanting to preserve the original identities of atoms.
For example:
>>> u = mda.Universe()`
>>> u.atoms.write('out.gro', reindex=False)
# OR
>>> with mda.Writer('out.gro', reindex=False) as w:
... w.write(u.atoms)
6.8.2. Classes
- class MDAnalysis.coordinates.GRO.Timestep(n_atoms, **kwargs)[source]
Timestep data for one frame
- Methods
ts = Timestep(n_atoms)
create a timestep object with space for n_atoms
Changed in version 0.11.0: Added
from_timestep()
andfrom_coordinates()
constructor methods.Timestep
init now only accepts integer creation.n_atoms
now a read only property.frame
now 0-based instead of 1-based. Attributes status and step removed.Changed in version 2.0.0: Timestep now can be (un)pickled. Weakref for Reader will be dropped. Timestep now stores in to numpy array memory in ‘C’ order rather than ‘F’ (Fortran).
Create a Timestep, representing a frame of a trajectory
- Parameters
n_atoms (int) – The total number of atoms this Timestep describes
positions (bool, optional) – Whether this Timestep has position information [
True
]velocities (bool (optional)) – Whether this Timestep has velocity information [
False
]forces (bool (optional)) – Whether this Timestep has force information [
False
]reader (Reader (optional)) – A weak reference to the owning Reader. Used for when attributes require trajectory manipulation (e.g. dt)
dt (float (optional)) – The time difference between frames (ps). If
time
is set, then dt will be ignored.time_offset (float (optional)) – The starting time from which to calculate time (in ps)
Changed in version 0.11.0: Added keywords for positions, velocities and forces. Can add and remove position/velocity/force information by using the
has_*
attribute.- copy_slice(sel)[source]
Make a new Timestep containing a subset of the original Timestep.
- Parameters
sel (array_like or slice) – The underlying position, velocity, and force arrays are sliced using a
list
,slice
, or any array-like.- Returns
A Timestep object of the same type containing all header information and all atom information relevant to the selection.
- Return type
Note
The selection must be a 0 based
slice
or array of the atom indices in thisTimestep
Example
Using a Python
slice
object:new_ts = ts.copy_slice(slice(start, stop, step))
Using a list of indices:
new_ts = ts.copy_slice([0, 2, 10, 20, 23])
New in version 0.8.
Changed in version 0.11.0: Reworked to follow new Timestep API. Now will strictly only copy official attributes of the Timestep.
- property dimensions
View of unitcell dimensions (A, B, C, alpha, beta, gamma)
lengths a, b, c are in the MDAnalysis length unit (Å), and angles are in degrees.
- property dt
The time difference in ps between timesteps
Note
This defaults to 1.0 ps in the absence of time data
New in version 0.11.0.
- property forces
A record of the forces of all atoms in this Timestep
Setting this attribute will add forces to the Timestep if they weren’t originally present.
- Returns
forces – force data of shape
(n_atoms, 3)
for all atoms- Return type
numpy.ndarray with dtype numpy.float32
- Raises
MDAnalysis.exceptions.NoDataError – if the Timestep has no force data
New in version 0.11.0.
- classmethod from_coordinates(positions=None, velocities=None, forces=None, **kwargs)[source]
Create an instance of this Timestep, from coordinate data
Can pass position, velocity and force data to form a Timestep.
New in version 0.11.0.
- classmethod from_timestep(other, **kwargs)[source]
Create a copy of another Timestep, in the format of this Timestep
New in version 0.11.0.
- property has_forces
A boolean of whether this Timestep has force data
This can be changed to
True
orFalse
to allocate space for or remove the data.New in version 0.11.0.
- property has_positions
A boolean of whether this Timestep has position data
This can be changed to
True
orFalse
to allocate space for or remove the data.New in version 0.11.0.
- property has_velocities
A boolean of whether this Timestep has velocity data
This can be changed to
True
orFalse
to allocate space for or remove the data.New in version 0.11.0.
- property n_atoms
A read only view of the number of atoms this Timestep has
Changed in version 0.11.0: Changed to read only property
- property positions
A record of the positions of all atoms in this Timestep
Setting this attribute will add positions to the Timestep if they weren’t originally present.
- Returns
positions – position data of shape
(n_atoms, 3)
for all atoms- Return type
numpy.ndarray with dtype numpy.float32
- Raises
MDAnalysis.exceptions.NoDataError – if the Timestep has no position data
Changed in version 0.11.0: Now can raise
NoDataError
when no position data present
- property time
The time in ps of this timestep
This is calculated as:
time = ts.data['time_offset'] + ts.time
Or, if the trajectory doesn’t provide time information:
time = ts.data['time_offset'] + ts.frame * ts.dt
New in version 0.11.0.
- property triclinic_dimensions
The unitcell dimensions represented as triclinic vectors
- Returns
A (3, 3) numpy.ndarray of unit cell vectors
- Return type
numpy.ndarray
Examples
The unitcell for a given system can be queried as either three vectors lengths followed by their respective angle, or as three triclinic vectors.
>>> ts.dimensions array([ 13., 14., 15., 90., 90., 90.], dtype=float32) >>> ts.triclinic_dimensions array([[ 13., 0., 0.], [ 0., 14., 0.], [ 0., 0., 15.]], dtype=float32)
Setting the attribute also works:
>>> ts.triclinic_dimensions = [[15, 0, 0], [5, 15, 0], [5, 5, 15]] >>> ts.dimensions array([ 15. , 15.81138802, 16.58312416, 67.58049774, 72.45159912, 71.56504822], dtype=float32)
New in version 0.11.0.
- property velocities
A record of the velocities of all atoms in this Timestep
Setting this attribute will add velocities to the Timestep if they weren’t originally present.
- Returns
velocities – velocity data of shape
(n_atoms, 3)
for all atoms- Return type
numpy.ndarray with dtype numpy.float32
- Raises
MDAnalysis.exceptions.NoDataError – if the Timestep has no velocity data
New in version 0.11.0.
- property volume
volume of the unitcell
- class MDAnalysis.coordinates.GRO.GROReader(filename, convert_units=True, n_atoms=None, **kwargs)[source]
Reader for the Gromacs GRO structure format.
Note
This Reader will only read the first frame present in a file.
Note
GRO files with zeroed 3 entry unit cells (i.e.
0.0 0.0 0.0
) are read as missing unit cell information. In these casesdimensions
will be set toNone
.Changed in version 0.11.0: Frames now 0-based instead of 1-based
Changed in version 2.0.0: Reader now only parses boxes defined with 3 or 9 fields. Reader now reads a 3 entry zero unit cell (i.e.
[0, 0, 0]
) as a being without dimension information (i.e. will the timestep dimension toNone
).
- class MDAnalysis.coordinates.GRO.GROWriter(filename, convert_units=True, n_atoms=None, **kwargs)[source]
GRO Writer that conforms to the Trajectory API.
- Will attempt to write the following information from the topology:
atom name (defaults to ‘X’)
resnames (defaults to ‘UNK’)
resids (defaults to ‘1’)
Note
The precision is hard coded to three decimal places.
Note
When dimensions are missing (i.e. set to None), a zero width unit cell box will be written (i.e. [0.0, 0.0, 0.0]).
Changed in version 0.11.0: Frames now 0-based instead of 1-based
Changed in version 0.13.0: Now strictly writes positions with 3dp precision. and velocities with 4dp. Removed the convert_dimensions_to_unitcell method, use Timestep.triclinic_dimensions instead. Now now writes velocities where possible.
Changed in version 0.18.0: Added reindex keyword argument to allow original atom ids to be kept.
Changed in version 2.0.0: Raises a warning when writing timestep with missing dimension information (i.e. set to
None
).Set up a GROWriter with a precision of 3 decimal places.
- Parameters
filename (str) – output filename
n_atoms (int (optional)) – number of atoms
convert_units (bool (optional)) – units are converted to the MDAnalysis base format; [
True
]reindex (bool (optional)) – By default, all the atoms were reindexed to have a atom id starting from 1. [
True
] However, this behaviour can be turned off by specifying reindex=False
.
Note
To use the reindex keyword, user can follow the two examples given below.:
u = mda.Universe()
Usage 1:
u.atoms.write('out.gro', reindex=False)
Usage 2:
with mda.Writer('out.gro', reindex=False) as w: w.write(u.atoms)
- fmt = {'box_orthorhombic': '{box[0]:10.5f} {box[1]:9.5f} {box[2]:9.5f}\n', 'box_triclinic': '{box[0]:10.5f} {box[4]:9.5f} {box[8]:9.5f} {box[1]:9.5f} {box[2]:9.5f} {box[3]:9.5f} {box[5]:9.5f} {box[6]:9.5f} {box[7]:9.5f}\n', 'n_atoms': '{0:5d}\n', 'xyz': '{resid:>5d}{resname:<5.5s}{name:>5.5s}{index:>5d}{pos[0]:8.3f}{pos[1]:8.3f}{pos[2]:8.3f}\n', 'xyz_v': '{resid:>5d}{resname:<5.5s}{name:>5.5s}{index:>5d}{pos[0]:8.3f}{pos[1]:8.3f}{pos[2]:8.3f}{vel[0]:8.4f}{vel[1]:8.4f}{vel[2]:8.4f}\n'}
format strings for the GRO file (all include newline); precision of 3 decimal places is hard-coded here.
- write(obj)[source]
Write selection at current trajectory frame to file.
Note
The GRO format only allows 5 digits for resid and atom number. If these numbers become larger than 99,999 then this routine will chop off the leading digits.
Changed in version 0.7.6: resName and atomName are truncated to a maximum of 5 characters
Changed in version 0.16.0: frame kwarg has been removed
Changed in version 2.0.0: Deprecated support for calling with Timestep has nwo been removed. Use AtomGroup or Universe as an input instead.
6.8.3. Developer notes: GROWriter
format strings
The GROWriter
class has a GROWriter.fmt
attribute, which is a dictionary of different
strings for writing lines in .gro
files. These are as follows:
n_atoms
For the first line of the gro file, supply the number of atoms in the system. E.g.:
fmt['n_atoms'].format(42)
xyz
An atom line without velocities. Requires that the ‘resid’, ‘resname’, ‘name’, ‘index’ and ‘pos’ keys be supplied. E.g.:
fmt['xyz'].format(resid=1, resname='SOL', name='OW2', index=2, pos=(0.0, 1.0, 2.0))
xyz_v
As above, but with velocities. Needs an additional keyword ‘vel’.
box_orthorhombic
The final line of the gro file which gives box dimensions. Requires the box keyword to be given, which should be the three cartesian dimensions. E.g.:
fmt['box_orthorhombic'].format(box=(10.0, 10.0, 10.0))
box_triclinic
As above, but for a non orthorhombic box. Requires the box keyword, but this time as a length 9 vector. This is a flattened version of the (3,3) triclinic vector representation of the unit cell. The rearrangement into the odd gromacs order is done automatically.