IBM ILOG Solver User's Manual > The Basics > Constraint Programming with IBM ILOG Solver > The three-stage method

The three-stage method

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To find a solution to a problem using IBM® ILOG® Solver, you use a three-stage method: describe, model, and solve.

The first stage is to describe the problem in natural language. For more information, see the section "Describe".

The second stage is to use Concert Technology classes to model the problem. The model is composed of decision variables and constraints. Decision variables are the unknown information in a problem. Each decision variable has a domain of possible values. The constraints are limits or restrictions on combinations of values for these decision variables. The model may also contain an objective, an expression that can be maximized or minimized. For more information, see the section "Model".

The third stage is to use Solver classes to solve the problem. Solving the problem consists of finding a value for each decision variable while simultaneously satisfying the constraints and maximizing or minimizing an objective, if one is included in the model. Solver uses two techniques for solving optimization problems: search strategies and constraint propagation. For more information, see the section "Solve".

In this lesson, you will describe, model, and solve a simple problem to understand the basic concepts in constraint programming. The problem is to find values for x and y from the following information:

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