Source code for pyretis.simulation.mc_simulation

# -*- coding: utf-8 -*-
# Copyright (c) 2021, PyRETIS Development Team.
# Distributed under the LGPLv2.1+ License. See LICENSE for more info.
"""Definition of simulation objects for Monte Carlo simulations.

This module defines some classes and functions for performing
Monte Carlo simulations.

Important classes defined here
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

UmbrellaWindowSimulation (:py:class:`.UmbrellaWindowSimulation`)
    Defines a simulation for performing umbrella window simulations.
    Several umbrella window simulations can be joined to perform a
    umbrella simulation.
"""
import numpy as np
from pyretis.core.montecarlo import max_displace_step
from pyretis.simulation.simulation import Simulation


__all__ = ['UmbrellaWindowSimulation']


def mc_task(rgen, system, maxdx):
    """Perform a Monte Carlo displacement move.

    Here, a displacement step will be carried out and
    the trial move will be accepted/rejected and the
    positions and potential energy will be updated as needed.

    Parameters
    ----------
    rgen : object like :py:class`.RandomGenerator`
        This object is used for generating random numbers.
    system : object like :py:class:`.System`
        The system we act on.
    maxdx : float
        Maximum displacement step for the Monte Carlo move.

    """
    accepted_r, _, trial_r, v_trial, status = max_displace_step(rgen, system,
                                                                maxdx)
    if status:
        system.particles.pos = accepted_r
        system.particles.vpot = v_trial
    return accepted_r, v_trial, trial_r, status


[docs]class UmbrellaWindowSimulation(Simulation): """This class defines an Umbrella simulation. The Umbrella simulation is a special case of the simulation class with settings to simplify the execution of the umbrella simulation. Attributes ---------- system : object like :py:class:`.System` The system to act on. umbrella : list = [float, float] The umbrella window. overlap : float The positions that must be crossed before the simulation is done. startcycle : int The current simulation cycle. mincycle : int The MINIMUM number of cycles to perform. rgen : object like :py:class:`.RandomGenerator` Object to use for random number generation. maxdx : float Maximum allowed displacement in the Monte Carlo step. """ simulation_type = 'umbrella-window'
[docs] def __init__(self, system, umbrella, overlap, maxdx, rgen=None, mincycle=0, startcycle=0): """Initialise the umbrella simulation simulation. Parameters ---------- system : object like :py:class:`.System` The system to act on. umbrella : list, [float, float] The umbrella window to consider. overlap : float The position we have to cross before the simulation is done. maxdx : float Defines the maximum movement allowed in the Monte Carlo moves. rgen : object like :py:class:`.RandomGenerator` Object to use for random number generation. mincycle : int, optional The *MINIMUM* number of cycles to perform. Note that in the base `Simulation` class this is the *MAXIMUM* number of cycles to perform. The meaning is redefined in this class by overriding `self.simulation_finished`. startcycle : int, optional The current simulation cycle, i.e. where we start. """ super().__init__(steps=mincycle, startcycle=startcycle) self.umbrella = umbrella self.overlap = overlap if rgen is None: self.rgen = np.random.RandomState() else: self.rgen = rgen self.system = system self.maxdx = maxdx self.add_task( { 'func': mc_task, 'args': [self.rgen, self.system, self.maxdx], 'result': 'displace_step', } ) self.first_step = False
[docs] def is_finished(self): """Check if the simulation is done. In the umbrella simulation, the simulation is finished when we cycle is larger than maxcycle and all particles have crossed self.overlap. Returns ------- out : boolean True if the simulation is finished, False otherwise. """ return (self.cycle['step'] > self.cycle['end'] and np.all(self.system.particles.pos > self.overlap))
[docs] def __str__(self): """Return some info about the simulation as a string.""" msg = ['Umbrella window simulation'] msg += ['Umbrella: {}, Overlap: {}.'.format(self.umbrella, self.overlap)] msg += ['Minimum number of cycles: {}'.format(self.cycle['end'])] return '\n'.join(msg)