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Grades 9–12 · Mathematics

How can linear optimization find the best allowed production plan?

Linear optimization seeks the largest or smallest value of a linear expression under stated restrictions. In a fictional workshop, x and y are amounts of batches A and B. Negative production is excluded. The quantities are divisible in this mathematical model, so a point between whole-number coordinates can also represent an allowed production amount.

N25 visual explanationFictional batch amounts satisfy x>=0, y>=0, x+y<=6 and 2x+y<=8. The objective is 3x+2y points. The feasible vertices are (0,0),(4,0),(2,4),(0,6), with scores 0, 12, 14, 12. The maximum is 14; maximizing vertices are (2,4). Continuous batches are assumed.Linear constraints define feasible productionx + y ≤ 6; 2x + y ≤ 8; x,y ≥ 0 · score 3x + 2yB0022446688Vertices(0,0) : 0(4,0) : 12(2,4) : 14(0,6) : 12A batchesMaximum objective: 14 points within the region.

In the diagramLinear constraints define feasible productionx + y ≤ 6; 2x + y ≤ 8; x,y ≥ 0 · score 3x + 2yB02468Vertices(0,0) : 0(4,0) : 12(2,4) : 14(0,6) : 12A batchesMaximum objective: 14 points within the region.

For objective 3x + 2y, the feasible vertex (2,4) gives the maximum of fourteen points.

Each A batch uses one material unit and two time units. Each B batch uses one of each. Six material units and eight time units give the constraints x + y ≤ 6 and 2x + y ≤ 8. A feasible point satisfies both inequalities and the nonnegative restrictions at once. Their intersection is the shaded region, not either half-plane alone.

The initial objective is 3x + 2y points. This expression assigns three points to each A batch and two to each B batch. The bounded feasible region has vertices (0,0), (4,0), (2,4) and (0,6). Their objective values are zero, twelve, fourteen and twelve. The largest is fourteen at (2,4).

For a bounded feasible polygon and a linear objective, at least one optimum occurs at a vertex. Sliding an equal-objective line toward larger values illustrates why the boundary matters. Sometimes an entire edge ties for the best value; changing the A coefficient to four produces that situation here. The optimum is a conclusion within the stated resource model, not a guarantee for an actual workshop.

About this explanation

Starting knowledge: Graph linear inequalities, solve two simultaneous equations and evaluate a linear expression.

Sources

  • Rice University, OpenStax — Linear programming: constraints, objective and feasible region
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