# Parma_Polyhedra_Library::Constraint Class Reference
[C++ Language Interface]

A linear equality or inequality. More...

`#include <ppl.hh>`

Inherits Parma_Polyhedra_Library::Linear_Row.

List of all members.

## Public Types

enum | Type { EQUALITY, NONSTRICT_INEQUALITY, STRICT_INEQUALITY }
| The constraint type. More...

## Public Member Functions

| Constraint (const Constraint &c)
| Ordinary copy-constructor.
| Constraint (const Congruence &cg)
| Copy-constructs from equality congruence `cg`.
| ~Constraint ()
| Destructor.
Constraint & | operator= (const Constraint &c)
| Assignment operator.
dimension_type | space_dimension () const
| Returns the dimension of the vector space enclosing `*this`.
Type | type () const
| Returns the constraint type of `*this`.
bool | is_equality () const
| Returns `true` if and only if `*this` is an equality constraint.
bool | is_inequality () const
| Returns `true` if and only if `*this` is an inequality constraint (either strict or non-strict).
bool | is_nonstrict_inequality () const
| Returns `true` if and only if `*this` is a non-strict inequality constraint.
bool | is_strict_inequality () const
| Returns `true` if and only if `*this` is a strict inequality constraint.
Coefficient_traits::const_reference | coefficient (Variable v) const
| Returns the coefficient of `v` in `*this`.
Coefficient_traits::const_reference | inhomogeneous_term () const
| Returns the inhomogeneous term of `*this`.
memory_size_type | total_memory_in_bytes () const
| Returns a lower bound to the total size in bytes of the memory occupied by `*this`.
memory_size_type | external_memory_in_bytes () const
| Returns the size in bytes of the memory managed by `*this`.
bool | is_tautological () const
| Returns `true` if and only if `*this` is a tautology (i.e., an always true constraint).
bool | is_inconsistent () const
| Returns `true` if and only if `*this` is inconsistent (i.e., an always false constraint).
bool | is_equivalent_to (const Constraint &y) const
| Returns `true` if and only if `*this` and `y` are equivalent constraints.
void | ascii_dump () const
| Writes to `std::cerr` an ASCII representation of `*this`.
void | ascii_dump (std::ostream &s) const
| Writes to `s` an ASCII representation of `*this`.
void | print () const
| Prints `*this` to `std::cerr` using `operator<<`.
bool | ascii_load (std::istream &s)
| Loads from `s` an ASCII representation (as produced by ascii_dump(std::ostream&) const) and sets `*this` accordingly. Returns `true` if successful, `false` otherwise.
bool | OK () const
| Checks if all the invariants are satisfied.
void | swap (Constraint &y)
| Swaps `*this` with `y`.

## Static Public Member Functions

static dimension_type | max_space_dimension ()
| Returns the maximum space dimension a Constraint can handle.
static void | initialize ()
| Initializes the class.
static void | finalize ()
| Finalizes the class.
static const Constraint & | zero_dim_false ()
| The unsatisfiable (zero-dimension space) constraint .
static const Constraint & | zero_dim_positivity ()
| The true (zero-dimension space) constraint , also known as positivity constraint.

## Friends

Constraint | operator== (const Linear_Expression &e1, const Linear_Expression &e2)
| Returns the constraint `e1` = `e2`.
Constraint | operator== (Variable v1, Variable v2)
| Returns the constraint `v1` = `v2`.
Constraint | operator== (const Linear_Expression &e, Coefficient_traits::const_reference n)
| Returns the constraint `e` = `n`.
Constraint | operator== (Coefficient_traits::const_reference n, const Linear_Expression &e)
| Returns the constraint `n` = `e`.
Constraint | operator>= (const Linear_Expression &e1, const Linear_Expression &e2)
| Returns the constraint `e1` >= `e2`.
Constraint | operator>= (Variable v1, Variable v2)
| Returns the constraint `v1` >= `v2`.
Constraint | operator>= (const Linear_Expression &e, Coefficient_traits::const_reference n)
| Returns the constraint `e` >= `n`.
Constraint | operator>= (Coefficient_traits::const_reference n, const Linear_Expression &e)
| Returns the constraint `n` >= `e`.
Constraint | operator<= (const Linear_Expression &e1, const Linear_Expression &e2)
| Returns the constraint `e1` <= `e2`.
Constraint | operator<= (const Linear_Expression &e, Coefficient_traits::const_reference n)
| Returns the constraint `e` <= `n`.
Constraint | operator<= (Coefficient_traits::const_reference n, const Linear_Expression &e)
| Returns the constraint `n` <= `e`.
Constraint | operator> (const Linear_Expression &e1, const Linear_Expression &e2)
| Returns the constraint `e1` > `e2`.
Constraint | operator> (Variable v1, Variable v2)
| Returns the constraint `v1` > `v2`.
Constraint | operator> (const Linear_Expression &e, Coefficient_traits::const_reference n)
| Returns the constraint `e` > `n`.
Constraint | operator> (Coefficient_traits::const_reference n, const Linear_Expression &e)
| Returns the constraint `n` > `e`.
Constraint | operator< (const Linear_Expression &e1, const Linear_Expression &e2)
| Returns the constraint `e1` < `e2`.
Constraint | operator< (const Linear_Expression &e, Coefficient_traits::const_reference n)
| Returns the constraint `e` < `n`.
Constraint | operator< (Coefficient_traits::const_reference n, const Linear_Expression &e)
| Returns the constraint `n` < `e`.

## Related Functions

(Note that these are not member functions.)
bool | operator== (const Constraint &x, const Constraint &y)
| Returns `true` if and only if `x` is equivalent to `y`.
bool | operator!= (const Constraint &x, const Constraint &y)
| Returns `true` if and only if `x` is not equivalent to `y`.
Constraint | operator<= (Variable v1, Variable v2)
| Returns the constraint `v1` <= `v2`.
Constraint | operator< (Variable v1, Variable v2)
| Returns the constraint `v1` < `v2`.
void | swap (Parma_Polyhedra_Library::Constraint &x, Parma_Polyhedra_Library::Constraint &y)
| Specializes `std::swap`.
std::ostream & | operator<< (std::ostream &s, const Constraint &c)
| Output operator.
std::ostream & | operator<< (std::ostream &s, const Constraint::Type &t)
| Output operator.

## Detailed Description

A linear equality or inequality.

An object of the class Constraint is either:

- an equality: ;
- a non-strict inequality: ; or
- a strict inequality: ;

where is the dimension of the space, is the integer coefficient of variable and is the integer inhomogeneous term.

How to build a constraint
  Constraints are typically built by applying a relation symbol to a pair of linear expressions. Available relation symbols are equality (`==`), non-strict inequalities (`>=` and `<=`) and strict inequalities (`<` and `>`). The space dimension of a constraint is defined as the maximum space dimension of the arguments of its constructor.

  In the following examples it is assumed that variables `x`, `y` and `z` are defined as follows:

        Variable x(0);
        Variable y(1);
        Variable z(2);

Example 1
  The following code builds the equality constraint , having space dimension :

        Constraint eq_c(3*x + 5*y - z == 0);

  The following code builds the (non-strict) inequality constraint , having space dimension :

        Constraint ineq_c(4*x >= 2*y - 13);

  The corresponding strict inequality constraint is obtained as follows:

        Constraint strict_ineq_c(4*x > 2*y - 13);

  An unsatisfiable constraint on the zero-dimension space can be specified as follows:

        Constraint false_c = Constraint::zero_dim_false();

  Equivalent, but more involved ways are the following:

        Constraint false_c1(Linear_Expression::zero() == 1);
        Constraint false_c2(Linear_Expression::zero() >= 1);
        Constraint false_c3(Linear_Expression::zero() > 0);

  In contrast, the following code defines an unsatisfiable constraint having space dimension :

        Constraint false_c(0*z == 1);

How to inspect a constraint
  Several methods are provided to examine a constraint and extract all the encoded information: its space dimension, its type (equality, non-strict inequality, strict inequality) and the value of its integer coefficients.

Example 2
  The following code shows how it is possible to access each single coefficient of a constraint. Given an inequality constraint (in this case ), we construct a new constraint corresponding to its complement (thus, in this case we want to obtain the strict inequality constraint ).

        Constraint c1(x - 5*y + 3*z <= 4);
        cout << "Constraint c1: " << c1 << endl;
        if (c1.is_equality())
          cout << "Constraint c1 is not an inequality." << endl;
        else {
          Linear_Expression e;
          for (dimension_type i = c1.space_dimension(); i-- > 0; )
            e += c1.coefficient(Variable(i)) * Variable(i);
          e += c1.inhomogeneous_term();
          Constraint c2 = c1.is_strict_inequality() ? (e <= 0) : (e < 0);
          cout << "Complement c2: " << c2 << endl;
        }

  The actual output is the following:

        Constraint c1: -A + 5*B - 3*C >= -4
        Complement c2: A - 5*B + 3*C > 4

  Note that, in general, the particular output obtained can be syntactically different from the (semantically equivalent) constraint considered.

## Member Enumeration Documentation

enum Parma_Polyhedra_Library::Constraint::Type

The constraint type.

Enumerator:

  EQUALITY | The constraint is an equality.
  NONSTRICT_INEQUALITY | The constraint is a non-strict inequality.
  STRICT_INEQUALITY | The constraint is a strict inequality.

## Constructor & Destructor Documentation

Parma_Polyhedra_Library::Constraint::Constraint | ( | const Congruence & | cg | ) | `[explicit]`

Copy-constructs from equality congruence `cg`.

Exceptions:

  | std::invalid_argument | Thrown if `cg` is a proper congruence.

## Member Function Documentation

Coefficient_traits::const_reference Parma_Polyhedra_Library::Constraint::coefficient | ( | Variable | v | ) | const`[inline]`

Returns the coefficient of `v` in `*this`.

Exceptions:

  | std::invalid_argument | thrown if the index of `v` is greater than or equal to the space dimension of `*this`.

bool Parma_Polyhedra_Library::Constraint::is_tautological | ( |  | ) | const

Returns `true` if and only if `*this` is a tautology (i.e., an always true constraint).

A tautology can have either one of the following forms:

- an equality: ; or
- a non-strict inequality: , where ; or
- a strict inequality: , where .

bool Parma_Polyhedra_Library::Constraint::is_inconsistent | ( |  | ) | const

Returns `true` if and only if `*this` is inconsistent (i.e., an always false constraint).

An inconsistent constraint can have either one of the following forms:

- an equality: , where ; or
- a non-strict inequality: , where ; or
- a strict inequality: , where .

bool Parma_Polyhedra_Library::Constraint::is_equivalent_to | ( | const Constraint & | y | ) | const

Returns `true` if and only if `*this` and `y` are equivalent constraints.

Constraints having different space dimensions are not equivalent. Note that constraints having different types may nonetheless be equivalent, if they both are tautologies or inconsistent.

## Friends And Related Function Documentation

Constraint operator== | ( | const Linear_Expression & | e1,
|  | const Linear_Expression & | e2 |
| ) |  |  | `[friend]`

Returns the constraint `e1` = `e2`.

Constraint operator== | ( | Variable | v1,
|  | Variable | v2 |
| ) |  |  | `[friend]`

Returns the constraint `v1` = `v2`.

Constraint operator== | ( | const Linear_Expression & | e,
|  | Coefficient_traits::const_reference | n |
| ) |  |  | `[friend]`

Returns the constraint `e` = `n`.

Constraint operator== | ( | Coefficient_traits::const_reference | n,
|  | const Linear_Expression & | e |
| ) |  |  | `[friend]`

Returns the constraint `n` = `e`.

Constraint operator>= | ( | const Linear_Expression & | e1,
|  | const Linear_Expression & | e2 |
| ) |  |  | `[friend]`

Returns the constraint `e1` >= `e2`.

Constraint operator>= | ( | Variable | v1,
|  | Variable | v2 |
| ) |  |  | `[friend]`

Returns the constraint `v1` >= `v2`.

Constraint operator>= | ( | const Linear_Expression & | e,
|  | Coefficient_traits::const_reference | n |
| ) |  |  | `[friend]`

Returns the constraint `e` >= `n`.

Constraint operator>= | ( | Coefficient_traits::const_reference | n,
|  | const Linear_Expression & | e |
| ) |  |  | `[friend]`

Returns the constraint `n` >= `e`.

Constraint operator<= | ( | const Linear_Expression & | e1,
|  | const Linear_Expression & | e2 |
| ) |  |  | `[friend]`

Returns the constraint `e1` <= `e2`.

Constraint operator<= | ( | const Linear_Expression & | e,
|  | Coefficient_traits::const_reference | n |
| ) |  |  | `[friend]`

Returns the constraint `e` <= `n`.

Constraint operator<= | ( | Coefficient_traits::const_reference | n,
|  | const Linear_Expression & | e |
| ) |  |  | `[friend]`

Returns the constraint `n` <= `e`.

Constraint operator> | ( | const Linear_Expression & | e1,
|  | const Linear_Expression & | e2 |
| ) |  |  | `[friend]`

Returns the constraint `e1` > `e2`.

Constraint operator> | ( | Variable | v1,
|  | Variable | v2 |
| ) |  |  | `[friend]`

Returns the constraint `v1` > `v2`.

Constraint operator> | ( | const Linear_Expression & | e,
|  | Coefficient_traits::const_reference | n |
| ) |  |  | `[friend]`

Returns the constraint `e` > `n`.

Constraint operator> | ( | Coefficient_traits::const_reference | n,
|  | const Linear_Expression & | e |
| ) |  |  | `[friend]`

Returns the constraint `n` > `e`.

Constraint operator< | ( | const Linear_Expression & | e1,
|  | const Linear_Expression & | e2 |
| ) |  |  | `[friend]`

Returns the constraint `e1` < `e2`.

Constraint operator< | ( | const Linear_Expression & | e,
|  | Coefficient_traits::const_reference | n |
| ) |  |  | `[friend]`

Returns the constraint `e` < `n`.

Constraint operator< | ( | Coefficient_traits::const_reference | n,
|  | const Linear_Expression & | e |
| ) |  |  | `[friend]`

Returns the constraint `n` < `e`.

bool operator== | ( | const Constraint & | x,
|  | const Constraint & | y |
| ) |  |  | `[related]`

Returns `true` if and only if `x` is equivalent to `y`.

bool operator!= | ( | const Constraint & | x,
|  | const Constraint & | y |
| ) |  |  | `[related]`

Returns `true` if and only if `x` is not equivalent to `y`.

Constraint operator<= | ( | Variable | v1,
|  | Variable | v2 |
| ) |  |  | `[related]`

Returns the constraint `v1` <= `v2`.

Constraint operator< | ( | Variable | v1,
|  | Variable | v2 |
| ) |  |  | `[related]`

Returns the constraint `v1` < `v2`.

void swap | ( | Parma_Polyhedra_Library::Constraint & | x,
|  | Parma_Polyhedra_Library::Constraint & | y |
| ) |  |  | `[related]`

Specializes `std::swap`.

std::ostream & operator<< | ( | std::ostream & | s,
|  | const Constraint & | c |
| ) |  |  | `[related]`

Output operator.

std::ostream & operator<< | ( | std::ostream & | s,
|  | const Constraint::Type & | t |
| ) |  |  | `[related]`

Output operator.

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

- ppl.hh