Class: Gecode::Constraints::Int::Arithmetic::SquareRootExpressionStub

Inherits:
CompositeStub show all
Defined in:
lib/gecoder/interface/constraints/int/arithmetic.rb

Overview

Describes a CompositeStub for the square root constraint, which constrain the rounded down square root of the variable.

Examples

# The square root of +x+, rounded down, must equal y.
x.square_root.must == y   

# The square root of +x+, rounded down, must be larger than 17, with 
# +bool+ as reification variable and +domain+ as strength.
x.square_root.must_be.larger_than(17, :reify => bool, :strength => :domain)

Instance Method Summary collapse

Methods inherited from CompositeStub

#initialize

Methods inherited from CompositeStub

#initialize

Methods included from LeftHandSideMethods

#must, #must_not

Methods inherited from ExpressionStub

#initialize

Constructor Details

This class inherits a constructor from Gecode::Constraints::Int::CompositeStub

Instance Method Details

#constrain_equal(variable, params, constrain) ⇒ Object 



124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
 
# File 'lib/gecoder/interface/constraints/int/arithmetic.rb', line 124

def constrain_equal(variable, params, constrain)
  lhs = @params[:lhs]
  if constrain
    max = lhs.max
    if max < 0
      # The left hand side does not have a real valued square root.
      upper_bound = 0
    else
      upper_bound = Math.sqrt(max).floor;
    end
    
    min = lhs.min
    if min < 0
      lower_bound = 0
    else
      lower_bound = Math.sqrt(min).floor;
    end
    
    variable.must_be.in lower_bound..upper_bound
  end

  Gecode::Raw::sqrt(@model.active_space, lhs.bind, variable.bind, 
    *propagation_options)
end