relaxed_newton.py

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# GNU General Public License for more details.
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# Copyright(C) 2013-2018 Max-Planck-Society
#
# NIFTy is being developed at the Max-Planck-Institut fuer Astrophysik
# and financially supported by the Studienstiftung des deutschen Volkes.

from .descent_minimizer import DescentMinimizer
from .line_search_strong_wolfe import LineSearchStrongWolfe


class RelaxedNewton(DescentMinimizer):
    """ Calculates the descent direction according to a Newton scheme.

    The descent direction is determined by weighting the gradient at the
    current parameter position with the inverse local metric.
    """
    def __init__(self, controller, line_searcher=None):
        if line_searcher is None:
            line_searcher = LineSearchStrongWolfe(
                preferred_initial_step_size=1.)
        super(RelaxedNewton, self).__init__(controller=controller,
                                            line_searcher=line_searcher)

    def get_descent_direction(self, energy):
        return -energy.metric.inverse_times(energy.gradient)