5. Global Constraint Catalogue

5.149. eq

DESCRIPTION

LINKS

Origin

Arithmetic.

Constraint

$𝚎𝚚 (𝚅𝙰𝚁 1, 𝚅𝙰𝚁 2)$

Synonym

$𝚡𝚎𝚚𝚢$ .

Arguments

$𝚅𝙰𝚁 1$	$𝚍𝚟𝚊𝚛$
$𝚅𝙰𝚁 2$	$𝚍𝚟𝚊𝚛$

Restriction

Purpose

Enforce the fact that two variables are equal.

Example

(8, 8)

The $𝚎𝚚$ constraint holds since 8 is equal to 8.

Symmetries

Arguments are permutable w.r.t. permutation $(𝚅𝙰𝚁 1, 𝚅𝙰𝚁 2)$ .
All occurrences of a value in $𝚅𝙰𝚁 1$ or $𝚅𝙰𝚁 2$ can be renamed to any unused value.

Arg. properties

Functional dependency: $𝚅𝙰𝚁 2$ determined by $𝚅𝙰𝚁 1$ .
Functional dependency: $𝚅𝙰𝚁 1$ determined by $𝚅𝙰𝚁 2$ .

Systems

eq in Choco, rel in Gecode, xeqy in JaCoP, #= in SICStus.

See also

common keyword: $𝚐𝚝$ , $𝚕𝚝$ (binary constraint,arithmetic constraint).

generalisation: $𝚊𝚕𝚕_𝚎𝚚𝚞𝚊𝚕$ (equality between more than two variables), $𝚎𝚚_𝚌𝚜𝚝$ ( $𝚌𝚘𝚗𝚜𝚝𝚊𝚗𝚝$ added), $𝚎𝚚_𝚜𝚎𝚝$ ( $𝚟𝚊𝚛𝚒𝚊𝚋𝚕𝚎$ replaced by $𝚜𝚎𝚝 𝚟𝚊𝚛𝚒𝚊𝚋𝚕𝚎$ ).

implies: $𝚊𝚋𝚜_𝚟𝚊𝚕𝚞𝚎$ , $𝚐𝚎𝚚$ , $𝚕𝚎𝚚$ , $𝚜𝚊𝚖𝚎_𝚜𝚒𝚐𝚗$ , $𝚣𝚎𝚛𝚘_𝚘𝚛_𝚗𝚘𝚝_𝚣𝚎𝚛𝚘$ .

negation: $𝚗𝚎𝚚$ .

Keywords

constraint arguments: binary constraint, pure functional dependency.

constraint type: predefined constraint, arithmetic constraint.

filtering: arc-consistency.

modelling: functional dependency.