Half-space

Definition

A half-space is a division of space created by a hyperplane, which separates the space into two distinct regions. One region contains all the points on one side of the hyperplane, while the other region contains points on the opposite side. This concept is crucial for understanding polytopes and their properties, as well as in exploring duality relationships and polar sets in geometry.

5 Must Know Facts For Your Next Test

1. Half-spaces are fundamental in defining convex polytopes, as every polytope can be represented as the intersection of a finite number of half-spaces.
2. The concept of half-spaces is vital in linear programming, where constraints can be represented as inequalities that define half-spaces.
3. Each half-space can be described using a linear inequality of the form $$a_1x_1 + a_2x_2 + ... + a_nx_n \geq b$$, where the coefficients define the orientation of the hyperplane.
4. In duality, half-spaces can be used to illustrate relationships between primal and dual representations of polytopes.
5. Half-spaces play an important role in defining polar sets, where the polar of a convex set can be viewed as the intersection of half-spaces defined by supporting hyperplanes.

Review Questions

• How do half-spaces contribute to the definition and representation of polytopes?
  • Half-spaces are essential in defining polytopes since a polytope can be described as the intersection of several half-spaces. Each half-space corresponds to a linear inequality that restricts the points that can be included in the polytope. By considering these intersections, we can visualize and analyze the structure and properties of polytopes more effectively.
• Discuss the significance of half-spaces in understanding duality and polar sets.
  • Half-spaces are crucial in understanding duality because they help to relate primal and dual forms of geometric representations. In this context, each half-space contributes to constructing both primal and dual polytopes. Additionally, when analyzing polar sets, half-spaces defined by supporting hyperplanes allow us to explore how these sets are characterized and differentiated within geometric spaces.
• Evaluate how half-spaces influence linear programming and optimization problems.
  • In linear programming, half-spaces serve as geometric representations of constraints imposed on decision variables. Each constraint translates into a half-space that defines feasible solutions in a multidimensional space. The intersection of these half-spaces forms a convex polytope representing possible solutions. Optimizing an objective function within this feasible region relies heavily on understanding these half-spaces, making them vital to finding optimal solutions in various applications.

Related terms

Hyperplane: A hyperplane is a subspace of one dimension less than its ambient space, used to separate space into different regions or half-spaces.

Convex Set: A convex set is a subset of a vector space where, for any two points within the set, the line segment connecting them also lies entirely within the set.

Supporting Hyperplane: A supporting hyperplane is a hyperplane that intersects a convex set at least at one point and separates the convex set from the external points.