The core.forces module

This submodule contains the Python bindings for the external forces.

`BaseForce`	The interface class for forces.
`RepulsiveSphere`	A confining repulsive sphere.
`LTCOMTrap`	A force acting between the centres of mass of groups of particles evaluated from a lookup table.
`LT2DCOMTrap`	A force acting between the centres of mass of groups of particles evaluated from a 2D lookup table.
`MovingTrap`	A harmonic force computed by using as a reference a point that optionally move with a constant velocity along a direction.

class oxpy.core.forces.BaseForce(self: oxpy.core.forces.BaseForce)

Bases: pybind11_object

The interface class for forces.

The default constructor takes no parameters.

as_RepulsiveSphere(self: oxpy.core.forces.BaseForce) → RepulsiveSphere

Attempt to cast the current force as a RepulsiveSphere object and return it.

Returns:: The force cast as a RepulsiveSphere or None if the casting fails.
Return type:: RepulsiveSphere

property group_name: The name of the group the force belongs to.

property id: The id of the force.

init(self: oxpy.core.forces.BaseForce, inp: oxpy.core.InputFile) → Tuple[List[int], str]

Initialise the force.

Parameters:: inp (input_file) – The input file of the simulation.

property pos0: The reference position associated to the force. The particular meaning of this attribute depends on the subclass external force.

potential(self: oxpy.core.forces.BaseForce, step: int, pos: LR_vector) → float

Return the potential energy due to the force at the given position and time step.

Parameters:

step (int) – The current time step.
pos (numpy.ndarray) – The position where the force should be computed.

Returns:

The computed potential energy.

Return type:

float

property rate: The rate of change of the force. The particular meaning of this attribute depends on the subclass external force.

property stiff: The stiffness (= strength) of the force. The particular meaning of this attribute depends on the subclass external force.

property type: the string used in the external force file to specify the force type (e.g. trap).

value(self: oxpy.core.forces.BaseForce, step: int, pos: LR_vector) → LR_vector

Return the force vector that would act at the given position and time step.

Parameters:

step (int) – The current time step.
pos (numpy.ndarray) – The position where the force should be computed.

Returns:

The computed force vector.

Return type:

numpy.ndarray

class oxpy.core.forces.LTCOMTrap

Bases: BaseForce

A force acting between the centres of mass of groups of particles evaluated from a lookup table.

property potential_grid: The lookup table used to interpolate the potential and the force.

class oxpy.core.forces.LT2DCOMTrap

Bases: BaseForce

A force acting between the centres of mass of groups of particles evaluated from a 2D lookup table.

The force is evaluated by using two collective variables that are the distances between two pairs of centres of mass.

property potential_grid: The lookup table used to interpolate the potential and the force.

class oxpy.core.forces.MovingTrap

Bases: BaseForce

A harmonic force computed by using as a reference a point that optionally move with a constant velocity along a direction.

property dir: The direction towards which the reference point moves.

property pos0: The initial position of the reference point.

property rate: The velocity (in units of time steps) with which the reference point moves. If set to 0 the point will remain in its initial position.

property stiff: The stiffness of the harmonic force.

class oxpy.core.forces.RepulsiveSphere

Bases: BaseForce

A confining repulsive sphere.

property center: The center of the sphere.

property r0: The initial radius of the sphere.

property r_ext: The radius beyond which the force is not felt any more.

property rate: The rate \(A\) with which the sphere radius grows over time with the relation \(r(t) = r_0 + At\), where \(t\) is the current time step.