Module variables

Contains the variables which are used by the Solver.

A variable, in the context of the solver, is a view onto a domain. It may forward domain information unaltered, or apply transformations which can be performed without the need of constraints.

We define 2 types of variables:

• Integer Variables (IntegerVariable) - These are represented by DomainIds when interacting with the Solver. These variables can be created using Solver::new_bounded_integer when creating a variable with the domain between a lower-bound and an upper-bound or using Solver::new_sparse_integer when creating a variable with holes in the domain. These variables can be transformed (according to the trait TransformableVariable) to create an AffineView.
• Propositional Variables (PropositionalVariable) - These specify booleans that can be used when interacting with the Solver. A Literal is used when a PropositionalVariable is given a polarity (i.e. it is the positive Literal or its negated version). A Literal can be created using Solver::new_literal.

Structs

• AffineView
  Models the constraint y = ax + b, by expressing the domain of y as a transformation of the domain of x.
• DomainId
  A structure which represents the most basic IntegerVariable; it is simply the id which links to a domain (hence the name).
• Literal
  A boolean variable in the solver; represents a PropositionalVariable but with a certain polarity (i.e. it is either the positive PropositionalVariable or its negation).
• PropositionalVariable
  A boolean variable in the solver; unlike Literal, this representation does not use a polarity.

Traits

• IntegerVariable
  A trait specifying the required behaviour of an integer variable such as retrieving a lower-bound (IntegerVariable::lower_bound) or adjusting the bounds (IntegerVariable::set_lower_bound).
• TransformableVariable
  Trait for transforming a variable