Source code for

Copyright 2013 Steven Diamond

This file is part of CVXPY.

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from cvxpy.constraints.constraint import Constraint
import cvxpy.lin_ops.lin_utils as lu
import numpy as np

[docs]class Zero(Constraint): """A constraint of the form :math:`x = 0`. The preferred way of creating a ``Zero`` constraint is through operator overloading. To constrain an expression ``x`` to be zero, simply write ``x == 0``. The former creates a ``Zero`` constraint with ``x`` as its argument. """ def __init__(self, expr, constr_id=None): super(Zero, self).__init__([expr], constr_id) def __str__(self): """Returns a string showing the mathematical constraint. """ return def __repr__(self): """Returns a string with information about the constraint. """ return "%s(%s)" % (self.__class__.__name__, repr(self.args[0])) @property def shape(self): """int : The shape of the constrained expression.""" return self.args[0].shape @property def size(self): """int : The size of the constrained expression.""" return self.args[0].size def name(self): return "%s == 0" % self.args[0]
[docs] def is_dcp(self): """A zero constraint is DCP if its argument is affine.""" return self.args[0].is_affine()
@property def residual(self): """The residual of the constraint. Returns ------- Expression """ if self.expr.value is None: return None return np.abs(self.expr.value) def canonicalize(self): """Returns the graph implementation of the object. Marks the top level constraint as the dual_holder, so the dual value will be saved to the EqConstraint. Returns: A tuple of (affine expression, [constraints]). """ obj, constraints = self.args[0].canonical_form dual_holder = lu.create_eq(obj, return (None, constraints + [dual_holder]) # The value of the dual variable. @property def dual_value(self): """NumPy.ndarray : The value of the dual variable. """ return self.dual_variables[0].value # TODO(akshayka): Rename to save_dual_value to avoid collision with # value as defined above. def save_value(self, value): """Save the value of the dual variable for the constraint's parent. Args: value: The value of the dual variable. """ self.dual_variables[0].save_value(value)