Objective Functions in AMPL

1. Description
2. Declaring an Objective Function
3. Defining an Objective Function

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).

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Declaring an Objective Function

Objective functions are declared using either the minimize or maximize keyword and a label:

minimize TotalCost;

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Defining an Objective Function

Objective functions are usually defined when they are declared, e.g.,

minimize TotalCost: sum {i in INGREDIENTS} Cost[i] * Amount[i];

However, in some cases (such as when models are defined by column), the objective function is defined later

minimize TotalWorkers;

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

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-- MichaelOSullivan - 02 Mar 2008