Class: Gecode::Constraints::Bool::BooleanConstraint

Inherits:
ReifiableConstraint show all
Defined in:
lib/gecoder/interface/constraints/bool/boolean.rb

Overview

Describes a constraint on a boolean expression.

Boolean expressions

A boolean expression consists of several boolean variable with various boolean operators. The available operators are:

|

Or

&

And

^

Exclusive or

implies

Implication

Examples

# +b1+ and +b2+
b1 & b2

# (+b1+ and +b2+) or +b3+ 
(b1 & b1) | b3

# (+b1+ and +b2+) or (+b3+ exclusive or +b1+)
(b1 & b2) | (b3 ^ b1)

# (+b1+ implies +b2+) and (+b3+ implies +b2+)
(b1.implies b2) & (b3.implies b2)

Domain

A domain constraint just specifies that a boolean expression must be true or false. Negation and reification are supported.

Examples

# +b1+ and +b2+ must be true.
(b1 & b2).must_be.true

# (+b1+ implies +b2+) and (+b3+ implies +b2+) must be false.
((b1.implies b2) & (b3.implies b2)).must_be.false

# +b1+ and +b2+ must be true. We reify it with +bool+ and select the
# strength +domain+.
(b1 & b2).must_be.true(:reify => bool, :strength => :domain)

Equality

A constraint with equality specifies that two boolean expressions must be equal. Negation and reification are supported. Any of ==, equal and equal_to may be used for equality.

Examples

# +b1+ and +b2+ must equal +b1+ or +b2+.
(b1 & b2).must == (b1 | b2)

# +b1+ and +b2+ must not equal +b3+. We reify it with +bool+ and select 
# the strength +domain+.
(b1 & b2).must_not.equal(b3, :reify => bool, :select => :domain)

Implication

A constraint using imply specified that one boolean expression must imply the other. Negation and reification are supported.

Examples

# +b1+ must imply +b2+
b1.must.imply b2

# +b1+ and +b2+ must not imply +b3+. We reify it with +bool+ and select
# +domain+ as strength.
(b1 & b2).must_not.imply b3

Instance Method Summary collapse

Methods inherited from ReifiableConstraint

#&, #reification_var, #reification_var=, #|

Methods inherited from Constraint

#initialize

Constructor Details

This class inherits a constructor from Gecode::Constraints::Constraint

Instance Method Details

#post ⇒ Object 



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# File 'lib/gecoder/interface/constraints/bool/boolean.rb', line 134

def post
  lhs, rhs, negate, reif_var = 
    @params.values_at(:lhs, :rhs, :negate, :reif)
  space = (lhs.model || rhs.model).active_space

  if lhs.kind_of?(Gecode::FreeBoolVar)
    lhs = Constraints::Bool::ExpressionNode.new(lhs, @model)
  end

  bot_eqv = Gecode::Raw::IRT_EQ
  bot_xor = Gecode::Raw::IRT_NQ

  if rhs.respond_to? :to_minimodel_bool_expr
    if reif_var.nil?
      tree = ExpressionTree.new(lhs, 
        Gecode::Raw::MiniModel::BoolExpr::NT_EQV, rhs)
      tree.to_minimodel_bool_expr.post(space, !negate, 
        *propagation_options)
    else
      tree = ExpressionTree.new(lhs, 
        Gecode::Raw::MiniModel::BoolExpr::NT_EQV, rhs)
      var = tree.to_minimodel_bool_expr.post(space, *propagation_options)
      Gecode::Raw::rel(space, var, (negate ? bot_xor : bot_eqv),
        reif_var.bind, *propagation_options)
    end
  else
    should_hold = !negate & rhs
    if reif_var.nil?
      lhs.to_minimodel_bool_expr.post(space, should_hold, 
        *propagation_options)
    else
      var = lhs.to_minimodel_bool_expr.post(space, *propagation_options)
      Gecode::Raw::rel(space, var, 
        (should_hold ? bot_eqv : bot_xor),
        reif_var.bind, *propagation_options)
    end
  end
end