Source code for picos.constraints.con_log

# coding: utf-8

# ------------------------------------------------------------------------------
# Copyright (C) 2018-2019 Maximilian Stahlberg
#
# This file is part of PICOS.
#
# PICOS is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
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# PICOS is distributed in the hope that it will be useful,
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
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"""Implementation of :class:`LogConstraint`."""

from collections import namedtuple

from .. import glyphs
from ..apidoc import api_end, api_start
from .constraint import Constraint, ConstraintConversion

_API_START = api_start(globals())
# -------------------------------


[docs]class LogConstraint(Constraint): """Lower bound on a logarithm."""
[docs] class ExpConeConversion(ConstraintConversion): """Bound on a logarithm to exponential cone constraint conversion."""
[docs] @classmethod def predict(cls, subtype, options): """Implement :meth:`~.constraint.ConstraintConversion.predict`.""" from . import AffineConstraint, ExpConeConstraint yield ("con", AffineConstraint.make_type(dim=1, eq=False), 1) yield ("con", ExpConeConstraint.make_type(), 1)
[docs] @classmethod def convert(cls, con, options): """Implement :meth:`~.constraint.ConstraintConversion.convert`.""" from ..expressions import ExponentialCone from ..modeling import Problem x = con.log.x t = con.lb P = Problem() P.add_constraint(x >= 0) P.add_constraint((x // 1 // t) << ExponentialCone()) return P
[docs] def __init__(self, log, lowerBound): """Construct a :class:`LogConstraint`. :param ~picos.expressions.Logarithm log: Constrained expression. :param ~picos.expressions.AffineExpression lowerBound: Lower bound on the expression. """ from ..expressions import AffineExpression, Logarithm assert isinstance(log, Logarithm) assert isinstance(lowerBound, AffineExpression) assert len(lowerBound) == 1 self.log = log self.lb = lowerBound super(LogConstraint, self).__init__("Logarithmic")
Subtype = namedtuple("Subtype", ()) def _subtype(self): return self.Subtype() @classmethod def _cost(cls, subtype): return 2 def _expression_names(self): yield "log" yield "lb" def _str(self): return glyphs.ge(self.log.string, self.lb.string) def _get_slack(self): return self.log.value - self.lb.value
# -------------------------------------- __all__ = api_end(_API_START, globals())