Coverage for picos/expressions/exp_logarithm.py: 74.14%
116 statements
« prev ^ index » next coverage.py v6.5.0, created at 2023-03-26 07:46 +0000
« prev ^ index » next coverage.py v6.5.0, created at 2023-03-26 07:46 +0000
1# ------------------------------------------------------------------------------
2# Copyright (C) 2019 Maximilian Stahlberg
3# Based on the original picos.expressions module by Guillaume Sagnol.
4#
5# This file is part of PICOS.
6#
7# PICOS is free software: you can redistribute it and/or modify it under the
8# terms of the GNU General Public License as published by the Free Software
9# Foundation, either version 3 of the License, or (at your option) any later
10# version.
11#
12# PICOS is distributed in the hope that it will be useful, but WITHOUT ANY
13# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
14# A PARTICULAR PURPOSE. See the GNU General Public License for more details.
15#
16# You should have received a copy of the GNU General Public License along with
17# this program. If not, see <http://www.gnu.org/licenses/>.
18# ------------------------------------------------------------------------------
20"""Implements :class:`Logarithm`."""
22import math
23import operator
24from collections import namedtuple
26import cvxopt
28from .. import glyphs
29from ..apidoc import api_end, api_start
30from ..constraints import LogConstraint
31from .data import convert_and_refine_arguments, convert_operands
32from .exp_affine import AffineExpression
33from .expression import Expression, refine_operands, validate_prediction
35_API_START = api_start(globals())
36# -------------------------------
39class Logarithm(Expression):
40 r"""Logarithm of a scalar affine expression.
42 :Definition:
44 For a real scalar affine expression :math:`x`, this is :math:`\log(x)`.
46 .. warning::
48 When you pose a lower bound on a logarithm :math:`\log(x)`, then PICOS
49 enforces :math:`x \geq 0` through an auxiliary constraint during
50 solution search.
51 """
53 # --------------------------------------------------------------------------
54 # Initialization and factory methods.
55 # --------------------------------------------------------------------------
57 @convert_and_refine_arguments("x")
58 def __init__(self, x):
59 """Construct a :class:`Logarithm`.
61 :param x: The scalar affine expression :math:`x`.
62 :type x: ~picos.expressions.AffineExpression
63 """
64 if not isinstance(x, AffineExpression):
65 raise TypeError("Can only take the logarithm of a real affine "
66 "expression, not of {}.".format(type(x).__name__))
67 elif not x.scalar:
68 raise TypeError("Can only take the logarithm of a scalar expression"
69 "but {} is shaped {}.".format(x.string, glyphs.shape(x.shape)))
71 self._x = x
73 Expression.__init__(self, "Logarithm", glyphs.log(x.string))
75 # --------------------------------------------------------------------------
76 # Abstract method implementations and method overridings, except _predict.
77 # --------------------------------------------------------------------------
79 def _get_refined(self):
80 if self._x.constant:
81 return AffineExpression.from_constant(self.value, 1, self._symbStr)
82 else:
83 return self
85 Subtype = namedtuple("Subtype", ())
87 def _get_subtype(self):
88 return self.Subtype()
90 def _get_value(self):
91 value = cvxopt.matrix(self._x._get_value()) # Must be dense for log.
92 return cvxopt.log(value)
94 def _get_mutables(self):
95 return self._x._get_mutables()
97 def _is_convex(self):
98 return False
100 def _is_concave(self):
101 return True
103 def _replace_mutables(self, mapping):
104 return self.__class__(self._x._replace_mutables(mapping))
106 def _freeze_mutables(self, freeze):
107 return self.__class__(self._x._freeze_mutables(freeze))
109 # --------------------------------------------------------------------------
110 # Python special method implementations, except constraint-creating ones.
111 # --------------------------------------------------------------------------
113 @classmethod
114 def _add(cls, self, other, forward):
115 if isinstance(other, AffineExpression) and other.constant:
116 if other.is0:
117 return self
119 log = cls(self._x * math.exp(other.value))
120 log._typeStr = "Offset " + log._typeStr
122 if forward:
123 log._symbStr = glyphs.clever_add(self.string, other.string)
124 else:
125 log._symbStr = glyphs.clever_add(other.string, self.string)
127 return log
129 if forward:
130 return Expression.__add__(self, other)
131 else:
132 return Expression.__radd__(self, other)
134 @convert_operands(scalarRHS=True)
135 @refine_operands()
136 def __add__(self, other):
137 return Logarithm._add(self, other, True)
139 @convert_operands(scalarRHS=True)
140 @refine_operands()
141 def __radd__(self, other):
142 return Logarithm._add(self, other, False)
144 @convert_operands(scalarRHS=True)
145 @refine_operands()
146 def __sub__(self, other):
147 if isinstance(other, AffineExpression) and other.constant:
148 log = Logarithm(self._x / math.exp(other.value))
149 log._typeStr = "Offset " + log._typeStr
150 log._symbStr = glyphs.clever_sub(self.string, other.string)
152 return log
154 return Expression.__sub__(self, other)
156 @classmethod
157 def _mul(cls, self, other, forward):
158 from . import Entropy, NegativeEntropy
160 if isinstance(other, AffineExpression):
161 if other.is0:
162 return AffineExpression.zero()
163 elif other.is1:
164 return self
165 elif other.equals(self._x):
166 return NegativeEntropy(self._x)
167 elif other.equals(-self._x):
168 return Entropy(self._x)
170 if forward:
171 return Expression.__mul__(self, other)
172 else:
173 return Expression.__rmul__(self, other)
175 @convert_operands(scalarRHS=True)
176 @refine_operands()
177 def __mul__(self, other):
178 return Logarithm._mul(self, other, True)
180 @convert_operands(scalarRHS=True)
181 @refine_operands()
182 def __rmul__(self, other):
183 return Logarithm._mul(self, other, False)
185 # --------------------------------------------------------------------------
186 # Methods and properties that return expressions.
187 # --------------------------------------------------------------------------
189 @property
190 def x(self):
191 """The expression :math:`x`."""
192 return self._x
194 @property
195 def exp(self):
196 """The exponential of the logarithm, equal to :math:`x`."""
197 return self._x
199 # --------------------------------------------------------------------------
200 # Constraint-creating operators, and _predict.
201 # --------------------------------------------------------------------------
203 @classmethod
204 def _predict(cls, subtype, relation, other):
205 assert isinstance(subtype, cls.Subtype)
207 if relation == operator.__ge__:
208 if issubclass(other.clstype, AffineExpression) \
209 and other.subtype.dim == 1:
210 return LogConstraint.make_type()
212 return NotImplemented
214 @convert_operands(scalarRHS=True)
215 @validate_prediction
216 @refine_operands()
217 def __ge__(self, other):
218 if isinstance(other, AffineExpression):
219 return LogConstraint(self, other)
220 else:
221 return NotImplemented
224# --------------------------------------
225__all__ = api_end(_API_START, globals())