.. _secMATLABrefCoinstraintInstance:

ConstraintInstance
==================

.. mat:class:: ConstraintInstance

The ConstraintInstance object stores the information regarding a specific instance of a costraint.
The instances can be accessed through the function :mat:meth:`Constraint.get` of the parent
entity.  



body()
------

.. mat:classmethod:: ConstraintInstance.body()

**Syntax**


``v = body()``
 
**Description**


``v = body()`` Get the current value of the constraint’s body.

**Output Arguments**


``v``
   The current body of the constraint.
   
**Example**

     
Create a constraint c (using :mat:meth:`AMPL.eval`), get an instance and display its body.

.. code-block:: matlab

   ampl.eval('var x{i in 1..2} := i*0.9;');
   ampl.eval('c{i in 1..2} : 0<= x[i] <= 5;');
   c1 = ampl.getConstraint('c').get(1);
   c1.body
   

   
gives::

   ans =
   0.9000  
    


dual
----

.. mat:classmethod:: ConstraintInstance.dual()

**Syntax**


``v = dual``
 
**Description**


``dual`` Get the current value of the constraint’s dual variable.


**Output Arguments**


``v``
   The value of the dual variable corresponding to the constraint

**Example**

     
Create a constraint c (using :mat:meth:`AMPL.eval`), get an instance and display its dual value.

.. code-block:: matlab

   ampl.eval('var x{i in 1..2} := i*0.9;');
   ampl.eval('c{i in 1..2} : 0<= x[i] <= 5;');
   c1 = ampl.getConstraint('c').get(1);
   c1.dual
   
   
gives::

    ans = 0

setDual(v)
----------

.. mat:classmethod:: Constraint.setDual()

**Syntax**


``setDual(v)``
 
**Description**


``setDual(v)`` Assigns the specified value to the dual variable.  Valid only for scalar constraints. Equivalent to the AMPL code::

   var x;
   c: x<=5;
   let c := v;


**Input Arguments**


``v``
   The value to be assigned 
   
**Example**

     
Create a constraint c and sets its dual value. We have to switch off AMPL presolve abilities to 
see the effect consistently.

.. code-block:: matlab

   ampl.setBoolOption('presolve', 0)
   ampl.eval('var x;');  
   ampl.eval('c: x <= 20;');
   c = ampl.getConstraint('c');
   c.setDual(4);
   c.dual
   
gives::

   ans =
     4
     

lb
--

.. mat:classmethod:: ConstraintInstance.lb()

**Syntax**


``v = lb``
 
**Description**


``lb`` Access the current lower bound of the constraint.


**Output Arguments**


``v``
   The lower bound of the constraint.

**Example**

     
Create a constraint c (using :mat:meth:`AMPL.eval`), get an instance and display its lower bound.

.. code-block:: matlab

   ampl.eval('var x{i in 1..2} := i*0.9;');
   ampl.eval('c{i in 1..2} : 0<= x[i] <= 5;');
   c1 = ampl.getConstraint('c').get(1);
   c1.lb
   
gives::

    ans = 0
    



ub
--

.. mat:classmethod:: ConstraintInstance.ub()

**Syntax**


``v = ub``
 
**Description**


``dual`` Access the current upper bound of the constraint.


**Output Arguments**


``v``
   The upper bound of the constraint

**Example**

     
Create a constraint c (using :mat:meth:`AMPL.eval`), get an instance and display its upper bound.

.. code-block:: matlab

   ampl.eval('var x{i in 1..2} := i*0.9;');
   ampl.eval('c{i in 1..2} : 0<= x[i] <= 5;');
   c1 = ampl.getConstraint('c').get(1);
   c1.ub
   
gives::

    ans = 5   

      

drop
----

.. mat:classmethod:: ConstraintInstance.drop()

**Syntax**


``drop``
 
**Description**


``drop`` Drop this instances of the constraint, corresponding to the AMPL code ``drop constraintname[index];``.

**Example**

     
Create an indexed constraint c (using :mat:meth:`AMPL.eval`) and drop one instance:

.. code-block:: matlab

   ampl.eval('var x{1..3}<=4;');
   ampl.eval('maximize z: sum{i in 1..3} x[i];');
   ampl.eval('c {i in 1..3} : x[i] <= i;');
   x = ampl.getVariable('x');
   ampl.solve;
   x.display
   ampl.getConstraint('c').get(2).drop
   ampl.solve;
   x.display
   
 gives::
 
   ans =
   x [*] :=
   1  1
   2  2
   3  3
   ;
    
   ans =
   x [*] :=
   1  1
   2  4
   3  3
   ;
    
    
   


restore
-------

.. mat:classmethod:: ConstraintInstance.restore()

**Syntax**


``restore``
 
**Description**


``restore`` Restore this instance of the constraint

**Example**

     
Create a constraint c, get an instance (c2), drop it and restore it, solving and displaying the values of the variables involved.

.. code-block:: matlab

   ampl.eval('var x{1..3}<=4;');
   ampl.eval('maximize z: sum{i in 1..3} x[i];');
   ampl.eval('c {i in 1..3} : x[i] <= i;');
   c2 = ampl.getConstraint('c').get(2);
   x = ampl.getVariable('x');
   
   c2.drop;
   ampl.solve;
   x.display
   
   c2.restore;
   ampl.solve;
   x.display


gives::
 
   x [*] :=
   1  1
   2  4
   3  3
   ;
    
    
   ans =
    
   x [*] :=
   1  1
   2  2
   3  3
   ;