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 2.

In all systems that we model, we will be faced with constraints which restrict the values of our variables. We can have many constraints. Each constraint will be a linear expression of our variables, with any appropriate coefficients, followed by the type of restriction and the value of the right hand side. We can think of a constraint looking like this:

The "Constraint Sense" will either be less than equal to (£), greater than equal to (³) or equal to (=). Note that we cannot have strict inequalities, i.e. we cannot use greater than (>) or less than (<).

The right hand side (RHS) will be the limiting value of this expression.

For example, we may have a budget for producing our three products. Let's assume that each product has a per unit production cost of $1, $2, and $5, respectively, and we have a budget of $300. An appropriate constraint would be:

Or maybe we have demand for the products that requires that we produce a combination of at least 50 units of p1 and p2. Then we would add the following constraint:

Note that not all variables need to appear in all constraints. We could also think of the above constraint as 1p1 + 1p2 + 0p3 ³ 50.

Let's also assume that we have exactly 400 hours of available production time and each unit requires 2, 4, and 5 hours of production time, respectively. Then we would write a constraint to say: