# hoomd.update#

Overview

 BoxResize Vary the simulation box size as a function of time. CustomUpdater User-defined updater. FilterUpdater Update sets of particles associated with a filter. RemoveDrift Remove the average drift from a restrained system.

Details

Updaters.

Updater operations modify the simulation state when they act.

class hoomd.update.BoxResize(trigger, box1=None, box2=None, variant=None, filter=hoomd._hoomd.ParticleFilter, box=None)#

Bases: Updater

Vary the simulation box size as a function of time.

Parameters:

BoxResize resizes the simulation box as a function of time. For each particle $$i$$ matched by filter, BoxResize scales the particle to fit in the new box:

$\vec{r}_i \leftarrow s_x \vec{a}_1' + s_y \vec{a}_2' + s_z \vec{a}_3' - \frac{\vec{a}_1' + \vec{a}_2' + \vec{a}_3'}{2}$

where $$\vec{a}_k'$$ are the new box vectors determined by box evaluated at the current time step and the scale factors are determined by the current particle position $$\vec{r}_i$$ and the previous box vectors $$\vec{a}_k$$:

$\vec{r}_i = s_x \vec{a}_1 + s_y \vec{a}_2 + s_z \vec{a}_3 - \frac{\vec{a}_1 + \vec{a}_2 + \vec{a}_3}{2}$

After scaling particles that match the filter, BoxResize wraps all particles $$j$$ back into the new box:

$\vec{r_j} \leftarrow \mathrm{minimum\_image}_{\vec{a}_k}' (\vec{r}_j)$

Note

For backward compatibility, you may set box1, box2, and variant which is equivalent to:

box = hoomd.variant.box.Interpolate(initial_box=box1,
final_box=box2,
variant=variant)

Warning

Rescaling particles in HPMC simulations with hard particles may introduce overlaps.

Note

When using rigid bodies, ensure that the BoxResize updater is last in the operations updater list. Immediately after the BoxResize updater triggers, rigid bodies (hoomd.md.constrain.Rigid) will be temporarily deformed. hoomd.md.Integrator will run after the last updater and resets the constituent particle positions before computing forces.

Deprecated since version 4.6.0: The arguments box1, box2, and variant are deprecated. Use box.

Example:

box_resize = hoomd.update.BoxResize(trigger=hoomd.trigger.Periodic(10),
box=inverse_volume_ramp)
simulation.operations.updaters.append(box_resize)
box#

The box as a function of time.

Example:

box_resize.box = inverse_volume_ramp
Type:

hoomd.variant.box.BoxVariant

filter#

The subset of particles to update.

Example:

filter_ = box_resize.filter
Type:

hoomd.filter.filter_like

property box1#

The box associated with the minimum of the passed variant.

Deprecated since version 4.6.0: Use box.

Type:

hoomd.Box

property box2#

The box associated with the maximum of the passed variant.

Deprecated since version 4.6.0: Use box.

Type:

hoomd.Box

get_box(timestep)#

Get the box for a given timestep.

Parameters:

timestep (int) – The timestep to use for determining the resized box.

Returns:

The box used at the given timestep. None before the first call to Simulation.run.

Return type:

Box

Example:

box = box_resize.get_box(1_000_000)
static update(state, box, filter=hoomd._hoomd.ParticleFilter)#

Immediately scale the particle in the system state to the given box.

Parameters:

Example:

hoomd.update.BoxResize.update(state=simulation.state,
box=box)
property variant#

A variant used to interpolate boxes.

Deprecated since version 4.6.0: Use box.

Type:

hoomd.variant.Variant

class hoomd.update.CustomUpdater(trigger, action)#

Bases: CustomOperation, Updater

User-defined updater.

Parameters:

CustomUpdater is a hoomd.operation.Updater that wraps a user-defined hoomd.custom.Action object so the action can be added to a hoomd.Operations instance for use with hoomd.Simulation objects.

Updaters modify the system state.

Example:

custom_updater = hoomd.update.CustomUpdater(
action=custom_action,
trigger=hoomd.trigger.Periodic(1000))
simulation.operations.updaters.append(custom_updater)
class hoomd.update.FilterUpdater(trigger, filters)#

Bases: Updater

Update sets of particles associated with a filter.

Parameters:

hoomd.Simulation caches the particles selected by hoomd.filter.filter_like objects to avoid the cost of re-running the filter on every time step. The particles selected by a filter will remain static until recomputed. This class provides a mechanism to update the cached list of particles. For example, periodically update a MD integration method’s group so that the integration method applies to particles in a given region of space.

Tip

To improve performance, use a hoomd.trigger.Trigger subclass, to update only when there is a known change to the particles that a filter would select.

Note

Some actions automatically recompute all filter particles such as adding or removing particles to the hoomd.Simulation.state.

Example:

filter_updater = hoomd.update.FilterUpdater(
trigger=hoomd.trigger.Periodic(1_000),
filters=[filter1, filter2])
__eq__(other)#

Return whether two objects are equivalent.

property filters#

filters to update select particles.

Example:

filter_updater.filters = [filter1, filter2]
Type:
class hoomd.update.RemoveDrift(reference_positions, trigger=1)#

Bases: Updater

Remove the average drift from a restrained system.

Parameters:

RemoveDrift computes the mean drift $$\vec{D}$$ from the given reference_positions ($$\vec{r}_{ref, i}$$):

$\vec{D} = \frac{1}{\mathrm{N_{particles}}} \sum_{i=0}^\mathrm{N_{particles-1}} \mathrm{minimum\_image}(\vec{r}_i - \vec{r}_{ref,i})$

RemoveDrift then shifts all particles in the system by $$-\vec{D}$$:

$\vec{r}_i \leftarrow \mathrm{minimum\_image}(\vec{r}_i - \vec{D})$

Tip

Use RemoveDrift with hoomd.hpmc.external.field.Harmonic to improve the accuracy of Frenkel-Ladd calculations.

Example:

remove_drift = hoomd.update.RemoveDrift(
reference_positions=[(0,0,0), (1,0,0)])
simulation.operations.updaters.append(remove_drift)
reference_positions#

the reference positions $$[\mathrm{length}]$$.

Example:

remove_drift.reference_positions = [(0,0,0), (1,0,0)]
Type:

(N_particles, 3) numpy.ndarray of float