delpi::Formula Class Reference

Symbolic formula used to represent a constraint in the LP problem. More...

#include <Formula.h>

Public Member Functions
Formula	Substitute (const Expression::SubstitutionMap &s) const
	Create a copy of this formula with the expression having all occurrences of the variables in s replaced with the corresponding variable in s.
template<MapFromTo< Variable, mpq_class > T>
bool	Evaluate (const T &env) const
	Evaluates the formula using a given environment (by default, an empty environment).

Public Attributes
Expression	expression_
	Left-hand side expression.
FormulaKind	kind_
	Kind of the formula \( \in \\{ =\, \ne\, \le\, \ge\, <\, > \\} \).
mpq_class	rhs_
	Right-hand side constant.

Detailed Description

Symbolic formula used to represent a constraint in the LP problem.

A symbolic formula is therefore a comparison between an expression and a constant. If two expressions are used as the left-hand side and right-hand side of the comparison, a new expression is created by subtracting the right-hand side from the left-hand side and the comparison is made with zero.

Variable x{"x"}, y{"y"}; // Variables
Formula row1 = x + 2 * y >= 0;
Formula row2 = x == 0;
Formula row3 = y != x;                 // row3 is equivalent to y - x != 0
Formula row4 = 2 * y - 5 * x < x + y;  // row4 is equivalent to 2 * y - 5 * x - (x + y) < 0

Definition at line 32 of file Formula.h.

Member Function Documentation

Evaluate()

template<MapFromTo< Variable, mpq_class > T>

template bool delpi::Formula::Evaluate ( const T & env ) const

nodiscard

Evaluates the formula using a given environment (by default, an empty environment).

Template Parameters

T	map from variable to value (i.e. std::map<Variable, mpq_class>, std::unordered_map<Variable, mpq_class>)

Parameters

env	map between each variable and its value

Returns

true if the formula is satisfied within the given environment

false if the formula is not satisfied within the given environment

Exceptions

std::exception

if there exists variable in this expression whose assignment is not provided by env

Definition at line 25 of file Formula.cpp.

Substitute()

Formula delpi::Formula::Substitute ( const Expression::SubstitutionMap & s ) const

nodiscard

Create a copy of this formula with the expression having all occurrences of the variables in s replaced with the corresponding variable in s.

Note that the substitutions occur simultaneously.

Formula f = x + 2 * y == 0;
Substitution s = {{x, y}, {y, x}};
f.Substitute(s);  // returns y + 2 * x == 0

Parameters

s	map of substitutions. Maps the old variable to the new one.

Returns

formula produced by the substitution

Definition at line 21 of file Formula.cpp.

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The documentation for this class was generated from the following files:

• delpi/symbolic/Formula.h
• delpi/symbolic/Formula.cpp