Source code for cvxpy.atoms.affine.unary_operators

"""
Copyright 2013 Steven Diamond

This file is part of CVXPY.

CVXPY 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.

CVXPY is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with CVXPY.  If not, see <http://www.gnu.org/licenses/>.
"""

from cvxpy.atoms.affine.affine_atom import AffAtom
import cvxpy.lin_ops.lin_utils as lu
import operator as op


class UnaryOperator(AffAtom):
    """
    Base class for expressions involving unary operators.
    """

    def __init__(self, expr):
        super(UnaryOperator, self).__init__(expr)

    def name(self):
        return self.OP_NAME + self.args[0].name()

    # Applies the unary operator to the value.
    def numeric(self, values):
        return self.OP_FUNC(values[0])


[docs]class NegExpression(UnaryOperator): """Negation of an expression. """ OP_NAME = "-" OP_FUNC = op.neg def shape_from_args(self): """Returns the (row, col) shape of the expression. """ return self.args[0].shape def sign_from_args(self): """Returns sign (is positive, is negative) of the expression. """ return (self.args[0].is_nonpos(), self.args[0].is_nonneg()) def is_incr(self, idx): """Is the composition non-decreasing in argument idx? """ return False def is_decr(self, idx): """Is the composition non-increasing in argument idx? """ return True def is_symmetric(self): """Is the expression symmetric? """ return self.args[0].is_symmetric() def is_hermitian(self): """Is the expression Hermitian? """ return self.args[0].is_hermitian() @staticmethod def graph_implementation(arg_objs, shape, data=None): """Negate the affine objective. Parameters ---------- arg_objs : list LinExpr for each argument. shape : tuple The shape of the resulting expression. data : Additional data required by the atom. Returns ------- tuple (LinOp for objective, list of constraints) """ return (lu.neg_expr(arg_objs[0]), [])