ObjectiveFunctionsInAMPL < OpsRes

Tags: view all tags
<!-- Ready to Review -->

---+<a name="top"></a> Objective Functions in AMPL

   1 [[#describe][Description]]
   2 [[#declare][Declaring an Objective Function]]
   3 [[#define][Defining an Objective Function]]

---++<a name="describe"></a> Description

The objective function of a mathematical programme is a function of the decision variables that measures the "worth" of the decisions. This "worth" is being either maximised or minimised (although, if no objective function is defined, AMPL will use the solver to search for a feasible solution).

[[#top][Return to top]]

---++<a name="declare"></a> Declaring an Objective Function

Objective functions are declared using either the =minimize= or =maximize= keyword and a label:
<pre>
minimize TotalCost;
</pre>

[[#top][Return to top]]

---++<a name="define"></a> Defining an Objective Function

Objective functions are usually defined when they are declared, e.g.,
<pre>
minimize TotalCost: sum {i in INGREDIENTS} Cost[i] * Amount[i];
</pre>

However, in some cases (such as when models are defined by column), the objective function is defined later
<pre>
minimize TotalWorkers;

var Work {j in SCHEDS} >= 0, integer,
  obj TotalWorkers 1,
  ...
 ;
</pre>

[[#top][Return to top]]

-- Main.MichaelOSullivan - 02 Mar 2008
Topic revision: r1 - 2008-03-02 - MichaelOSullivan