.. _secMATLABrefVariableInstance:

VariableInstance
================

.. mat:class:: VariableInstance

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




value()
-------

.. mat:classmethod:: VariableInstance.value()

**Syntax**


``v = value()``
 
**Description**


``v = value()`` Get the current value of the variable instance 

**Output Arguments**


``v``
   The current value of the variable instance
   
**Example**

     
Create a variable x, get an instance and display its value.

.. code-block:: matlab

   ampl.eval('var x{1..2};');  
   x = ampl.getVariable('x');
   instance = x.get(1);
   instance.value
   
gives::

   ans =
     0
     
     
setValue(v)
-----------

.. mat:classmethod:: VariableInstance.setValue()

**Syntax**


``setValue(v)``
 
**Description**


``setValue(v)`` Assigns the specified value to the variable. Equivalent to the AMPL code::

   var x;
   let x := v;


**Input Arguments**


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

     
Create a variable x and sets its initial value. Then displays it:

.. code-block:: matlab

   ampl.eval('var x{1..2};');  
   x = ampl.getVariable('x');
   instance = x.get(1);
   instance.setValue(4);
   instance.value
   
gives::

   ans =
     4





dual
----

.. mat:classmethod:: VariableInstance.dual()

**Syntax**


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


``dual`` Get the current dual value of the variable instance. 


**Output Arguments**


``v``
   The dual value of the instance

**Example**

     
Create a variable x, get an instance and display its dual value.

.. code-block:: matlab

   ampl.eval('var x{1..2};');  
   x = ampl.getVariable('x');
   instance = x.get(1);
   instance.dual
   
gives::

   ans =
     0


lb
--

.. mat:classmethod:: VariableInstance.lb()

**Syntax**


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


``lb`` Get the current lower bound of the variable. See :ref:`secVariableSuffixesNotes`.


**Output Arguments**


``v``
   The lower bound of the variable

**Example**

     
Create an indexed variable x (using :mat:meth:`AMPL.eval`) and get the value of the lower bound.

.. code-block:: matlab

   ampl.eval('var x{1..3};');  
   x = ampl.getVariable('x');
   instance = x.get(1);
   v = instance.lb
   
gives::

    v = 0
    


ub
--

.. mat:classmethod:: VariableInstance.ub()

**Syntax**


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


``ub`` Get the current upper bound of the instance. See :ref:`secVariableSuffixesNotes`.  


**Output Arguments**


``v``
   The upper bound of the instance

**Example**

     
Create an indexed variable y (:mat:meth:`AMPL.eval`) and get the value of one instance.

.. code-block:: matlab

   ampl.eval('var x{1..3};');  
   x = ampl.getVariable('x');
   instance = x.get(1);
   v = instance.lb
   
gives::

    v = 0    





fix
---

.. mat:classmethod:: VariableInstance.fix()

**Syntax**


``fix``

``fix(value)``
 
**Description**


``fix`` Fix this instance to its current value

``fix(value)`` Fix this instance to the specified value

**Example**

     
Create a scalar variable x and an indexed variable y (using :mat:meth:`AMPL.eval`), fix 
a few values, solve and unfix them

.. code-block:: matlab

   ampl.eval('var x<=3; var y{1..3}<=4;');
   ampl.eval('maximize z: x + sum{i in 1..3} y[i];');
   x = ampl.getVariable('x');
   y = ampl.getVariable('y');
   x.fix(1);         % fix variables
   y.get(2).fix(2);
   ampl.solve; % solve
   x.display   % display solution
   y.display
   x.unfix;    % unfix variables
   y.unfix;
   ampl.solve; % solve and display
   x.display   % display solution
   y.display
   
 gives::
 
   ans =
      x = 1
       
   ans =       
      y [*] :=
      1  4
      2  2
      3  4
      ;
       
   ans =    
      x = 3
       
   ans =    
      y [*] :=
      1  4
      2  4
      3  4
      ;



unfix
-----

.. mat:classmethod:: VariableInstance.unfix()

**Syntax**


``unfix``
 
**Description**


``unfix`` Unfix this instance

**Example**

     
Create a scalar variable x and an indexed variable y (using :mat:meth:`AMPL.eval`), fix 
a few values, solve and unfix them

.. code-block:: matlab

   ampl.eval('var x<=3; var y{1..3}<=4;');
   ampl.eval('maximize z: x + sum{i in 1..3} y[i];');
   x = ampl.getVariable('x');
   y = ampl.getVariable('y');
   x.fix(1);         % fix variables
   y.get(2).fix(2);
   ampl.solve; % solve
   x.display   % display solution
   y.display
   x.unfix;    % unfix variables
   y.unfix;
   ampl.solve; % solve and display
   x.display   % display solution
   y.display
   
 gives::
 
   ans =
      x = 1
       
   ans =       
      y [*] :=
      1  4
      2  2
      3  4
      ;
       
   ans =    
      x = 3
       
   ans =    
      y [*] :=
      1  4
      2  4
      3  4
      ;