Class: Gecode::Constraints::Int::Linear::LinearConstraint

Inherits:
ReifiableConstraint show all
Defined in:
lib/gecoder/interface/constraints/int/linear.rb

Overview

Linear constraints specify that an integer variable must have a linear equation containing variables must hold. The same relations and options used in SimpleRelationConstraint can also be used for linear constraints.

Boolean variables can also be used instead of integer variables. In that case a boolean variable assigned true is equal to 1 and a boolean variable assigned false is equal to 0. There is one exception: boolean variables can not be used alone as left hand side.

Do not mix boolean and integer variables. Even if possible it’s not supported, and might be removed in the future.

Examples

# The sum of the int variables +x+ and +y+ must equal +z+ + 3.
(x + y).must == z + 3

# Another way of writing the above. 
z.must == x + y - 3

# The inequality 10(x + y) > 3x must not hold. 
(x + y)*10.must_not > x*3

# Specifies the above, but reifies the constraint with the boolean 
# variable +bool+ and gives it propagation strength +domain+.
(x + y)*10.must_not_be.greater_than(x*3, :reify => bool, :strength => :domain)

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 



143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
 
# File 'lib/gecoder/interface/constraints/int/linear.rb', line 143

def post
  lhs, rhs, relation_type, reif_var = 
    @params.values_at(:lhs, :rhs, :relation_type, :reif)
  reif_var = reif_var.bind if reif_var.respond_to? :bind
  if rhs.respond_to? :to_minimodel_lin_exp
    rhs = rhs.to_minimodel_lin_exp
  elsif rhs.respond_to? :bind
    rhs = rhs.bind * 1
  end

  final_exp = (lhs.to_minimodel_lin_exp - rhs)
  if reif_var.nil?
    final_exp.post(@model.active_space, relation_type, 
      *propagation_options)
  else
    final_exp.post(@model.active_space, relation_type, reif_var, 
      *propagation_options)
  end
end