Chimie Théorique » QMX

# -*- coding: utf-8 -*-

import sys

import numpy as np

from ase.optimize.optimize import Optimizer

from ase.utils.linesearch import LineSearch

class LBFGS(Optimizer):

    """Limited memory BFGS optimizer.

    A limited memory version of the bfgs algorithm. Unlike the bfgs algorithm

    used in bfgs.py, the inverse of Hessian matrix is updated.  The inverse

    Hessian is represented only as a diagonal matrix to save memory

    """

    def __init__(self, atoms, restart=None, logfile='-', trajectory=None,

                 maxstep=None, memory=100, damping = 1.0, alpha = 10.0,

                 use_line_search=False):

        """

        Parameters:

        restart: string

            Pickle file used to store vectors for updating the inverse of Hessian

            matrix. If set, file with such a name will be searched and information

            stored will be used, if the file exists.

        logfile: string

            Where should output go. None for no output, '-' for stdout.

        trajectory: string

            Pickle file used to store trajectory of atomic movement.

        maxstep: float

            How far is a single atom allowed to move. This is useful for DFT

            calculations where wavefunctions can be reused if steps are small.

            Default is 0.04 Angstrom.

        memory: int

            Number of steps to be stored. Default value is 100. Three numpy

            arrays of this length containing floats are stored.

        damping: float

            The calculated step is multiplied with this number before added to

            the positions.

        alpha: float

            Initial guess for the Hessian (curvature of energy surface). A

            conservative value of 70.0 is the default, but number of needed

            steps to converge might be less if a lower value is used. However,

            a lower value also means risk of instability.

        """

        Optimizer.__init__(self, atoms, restart, logfile, trajectory)

        if maxstep is not None:

            if maxstep > 1.0:

                raise ValueError('You are using a much too large value for ' +

                                 'the maximum step size: %.1f Angstrom' % maxstep)

            self.maxstep = maxstep

        else:

            self.maxstep = 0.04

        self.memory = memory

        self.H0 = 1. / alpha  # Initial approximation of inverse Hessian

                            # 1./70. is to emulate the behaviour of BFGS

                            # Note that this is never changed!

        self.damping = damping

        self.use_line_search = use_line_search

        self.p = None

        self.function_calls = 0

        self.force_calls = 0

    def initialize(self):

        """Initalize everything so no checks have to be done in step"""

        self.iteration = 0

        self.s = []

        self.y = []

        self.rho = [] # Store also rho, to avoid calculationg the dot product

                      # again and again

        self.r0 = None

        self.f0 = None

        self.e0 = None

        self.task = 'START'

        self.load_restart = False

    def read(self):

        """Load saved arrays to reconstruct the Hessian"""

        self.iteration, self.s, self.y, self.rho, \

        self.r0, self.f0, self.e0, self.task = self.load()

        self.load_restart = True

    def step(self, f):

        """Take a single step

        Use the given forces, update the history and calculate the next step --

        then take it"""

        r = self.atoms.get_positions()

        p0 = self.p

        self.update(r, f, self.r0, self.f0)

        s = self.s

        y = self.y

        rho = self.rho

        H0 = self.H0

        loopmax = np.min([self.memory, self.iteration])

        a = np.empty((loopmax,), dtype=np.float64)

        ### The algorithm itself:

        q = - f.reshape(-1)

        for i in range(loopmax - 1, -1, -1):

            a[i] = rho[i] * np.dot(s[i], q)

            q -= a[i] * y[i]

        z = H0 * q

        for i in range(loopmax):

            b = rho[i] * np.dot(y[i], z)

            z += s[i] * (a[i] - b)

        self.p = - z.reshape((-1, 3))

        ###

        g = -f

        if self.use_line_search == True:

            e = self.func(r)

            self.line_search(r, g, e)

            dr = (self.alpha_k * self.p).reshape(len(self.atoms),-1)

        else:

            self.force_calls += 1

            self.function_calls += 1

            dr = self.determine_step(self.p) * self.damping

        self.atoms.set_positions(r+dr)

        self.iteration += 1

        self.r0 = r

        self.f0 = -g

        self.dump((self.iteration, self.s, self.y,

                   self.rho, self.r0, self.f0, self.e0, self.task))

    def determine_step(self, dr):

        """Determine step to take according to maxstep

        Normalize all steps as the largest step. This way

        we still move along the eigendirection.

        """

        steplengths = (dr**2).sum(1)**0.5

        longest_step = np.max(steplengths)

        if longest_step >= self.maxstep:

            dr *= self.maxstep / longest_step

        return dr

    def update(self, r, f, r0, f0):

        """Update everything that is kept in memory

        This function is mostly here to allow for replay_trajectory.

        """

        if self.iteration > 0:

            s0 = r.reshape(-1) - r0.reshape(-1)

            self.s.append(s0)

            # We use the gradient which is minus the force!

            y0 = f0.reshape(-1) - f.reshape(-1)

            self.y.append(y0)

            rho0 = 1.0 / np.dot(y0, s0)

            self.rho.append(rho0)

        if self.iteration > self.memory:

            self.s.pop(0)

            self.y.pop(0)

            self.rho.pop(0)

    def replay_trajectory(self, traj):

        """Initialize history from old trajectory."""

        if isinstance(traj, str):

            from ase.io.trajectory import PickleTrajectory

            traj = PickleTrajectory(traj, 'r')

        r0 = None

        f0 = None

        # The last element is not added, as we get that for free when taking

        # the first qn-step after the replay

        for i in range(0, len(traj) - 1):

            r = traj[i].get_positions()

            f = traj[i].get_forces()

            self.update(r, f, r0, f0)

            r0 = r.copy()

            f0 = f.copy()

            self.iteration += 1

        self.r0 = r0

        self.f0 = f0

    def func(self, x):

        """Objective function for use of the optimizers"""

        self.atoms.set_positions(x.reshape(-1, 3))

        self.function_calls += 1

        return self.atoms.get_potential_energy()

    def fprime(self, x):

        """Gradient of the objective function for use of the optimizers"""

        self.atoms.set_positions(x.reshape(-1, 3))

        self.force_calls += 1

        # Remember that forces are minus the gradient!

        return - self.atoms.get_forces().reshape(-1)

    def line_search(self, r, g, e):

        self.p = self.p.ravel()

        p_size = np.sqrt((self.p **2).sum())

        if p_size <= np.sqrt(len(self.atoms) * 1e-10):

            self.p /= (p_size / np.sqrt(len(self.atoms)*1e-10))

        g = g.ravel()

        r = r.ravel()

        ls = LineSearch()

        self.alpha_k, e, self.e0, self.no_update = \

           ls._line_search(self.func, self.fprime, r, self.p, g, e, self.e0,

                           maxstep=self.maxstep, c1=.23,

                           c2=.46, stpmax=50.)

class LBFGSLineSearch(LBFGS):

    """This optimizer uses the LBFGS algorithm, but does a line search that fulfills

    the Wolff conditions.

    """

    def __init__(self, *args, **kwargs):

        kwargs['use_line_search'] = True

        LBFGS.__init__(self, *args, **kwargs)

#    """Modified version of LBFGS.

#

#    This optimizer uses the LBFGS algorithm, but does a line search for the

#    minimum along the search direction. This is done by issuing an additional

#    force call for each step, thus doubling the number of calculations.

#

#    Additionally the Hessian is reset if the new guess is not sufficiently

#    better than the old one.

#    """

#    def __init__(self, *args, **kwargs):

#        self.dR = kwargs.pop('dR', 0.1)

#        LBFGS.__init__(self, *args, **kwargs)

#

#    def update(self, r, f, r0, f0):

#        """Update everything that is kept in memory

#

#        This function is mostly here to allow for replay_trajectory.

#        """

#        if self.iteration > 0:

#            a1 = abs(np.dot(f.reshape(-1), f0.reshape(-1)))

#            a2 = np.dot(f0.reshape(-1), f0.reshape(-1))

#            if not (a1 <= 0.5 * a2 and a2 != 0):

#                # Reset optimization

#                self.initialize()

#

#        # Note that the reset above will set self.iteration to 0 again

#        # which is why we should check again

#        if self.iteration > 0:

#            s0 = r.reshape(-1) - r0.reshape(-1)

#            self.s.append(s0)

#

#            # We use the gradient which is minus the force!

#            y0 = f0.reshape(-1) - f.reshape(-1)

#            self.y.append(y0)

#

#            rho0 = 1.0 / np.dot(y0, s0)

#            self.rho.append(rho0)

#

#        if self.iteration > self.memory:

#            self.s.pop(0)

#            self.y.pop(0)

#            self.rho.pop(0)

#

#    def determine_step(self, dr):

#        f = self.atoms.get_forces()

#

#        # Unit-vector along the search direction

#        du = dr / np.sqrt(np.dot(dr.reshape(-1), dr.reshape(-1)))

#

#        # We keep the old step determination before we figure

#        # out what is the best to do.

#        maxstep = self.maxstep * np.sqrt(3 * len(self.atoms))

#

#        # Finite difference step using temporary point

#        self.atoms.positions += (du * self.dR)

#        # Decide how much to move along the line du

#        Fp1 = np.dot(f.reshape(-1), du.reshape(-1))

#        Fp2 = np.dot(self.atoms.get_forces().reshape(-1), du.reshape(-1))

#        CR = (Fp1 - Fp2) / self.dR

#        #RdR = Fp1*0.1

#        if CR < 0.0:

#            #print "negcurve"

#            RdR = maxstep

#            #if(abs(RdR) > maxstep):

#            #    RdR = self.sign(RdR) * maxstep

#        else:

#            Fp = (Fp1 + Fp2) * 0.5

#            RdR = Fp / CR

#            if abs(RdR) > maxstep:

#                RdR = np.sign(RdR) * maxstep

#            else:

#                RdR += self.dR * 0.5

#        return du * RdR

class HessLBFGS(LBFGS):

    """Backwards compatibiliyt class"""

    def __init__(self, *args, **kwargs):

        if 'method' in kwargs:

            del kwargs['method']

        sys.stderr.write('Please use LBFGS instead of HessLBFGS!')

        LBFGS.__init__(self, *args, **kwargs)

class LineLBFGS(LBFGSLineSearch):

    """Backwards compatibiliyt class"""

    def __init__(self, *args, **kwargs):

        if 'method' in kwargs:

            del kwargs['method']

        sys.stderr.write('Please use LBFGSLineSearch instead of LineLBFGS!')

        LBFGSLineSearch.__init__(self, *args, **kwargs)