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We first introduce the concepts of polyhedral cone and polytope. Next, similarly to the algebra course I, an algorithm, which obtains the dual cone of a given cone and all its facets of any dimension, allows us to solve all discussed problems of linear algebra using the duality concept as a new point of view. This duality point of view allow us to solve the cone membership of a vector and the intersection of cones in a very simple way. In addition, the algorithm provides the dual cone in its simplest form, that is, as a linear space with its basis plus an acute cone with its edges. The compatibility of a linear system of inequalities is discussed and all the solutions of linear systems of inequalities are obtained. In addition, the solutions of all subsystems including all equations from the first to any of them are obtained at once. The concept of cone associated with a polytope permits us to obtain all vertices and all facets of any dimension of a polytope. The set of all feasible solutions of a linear programming problem and all its optimal solutions are obtained, and infeasibility is detected by the algorithm. Finally an example of a water supply problem is presented to show the importance of these methods in engineering design.
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In this first block the presentation of the course will be made, exposing the block structure of the same and its sequential planning.
A course of Algebra including cones, polytopes and systems of linear inequalities.
Enrique Castillo
Motivating a linear algebra course based on duality and the dual cone concept
In this first block the polytope and cone algebraic structures are presented, showing some illustrative examples that facilitate their understanding. The concept of a dual cone of a given cone is also presented. As a fundamental element for the development of the course, the algorithm for obtaining the dual cone of a given cone is described, which although designed to obtain the dual cone, will serve as the basis for solving all the other problems that arise in the course. It is shown that the vector space is a particular case of cone and that it is enough to add one more generator to the base in order to express the vectors of the vector space as cone, that is, generated by nonnegative linear combinations. Finally, the standard form of a cone is defined as the sum of its components of vector space and acute cone, which allows expressing the cone in its minimal form.
Polyhedral convex cones and polytopes
Algorithm to obtain the dual cone of a given cone
Algorithm to obtain the dual of a cone in standard form
Standard form of a cone
This second block is focused on the algebraic applications of the algorithm, which include: the problem of the membership of a vector to a cone and the intersection of two cones. The first of these is a complex problem because it involves nonnegative linear combinations, that is, systems of linear inequations, whose solutions are not usually known by students or studied in standard algebra courses. The use of the algorithm, explained in the previous block, allows to solve the problem in a very elegant way and avoid having to solve these systems. The intersection of cones is another problem of some complexity, since it also implies the systems of inequations, solving it in an ingenious way. It can also be resolved by realizing that such an intersection is the dual cone of the dual of one of them in the other, which directly suggests how to solve it.
Vector Membership of a cone
Intersection of two polyhedral cones
This block focuses on linear inequation systems, including homogeneous and complete systems. It also explains how all the subsystems of a given system can be solved simultaneously, as well as how to analyze the compatibility of a system, that is, whether or not it has a solution.Content
Homogeneous linear systems of inequalities
Solving complete linear systems of inequalities
Compatibility of complete linear systems of inequalities
Equations of a polyhedron
Sets of solutions of linear systems of inequalities
Cone associated with a polytope. Facets of cones and polytopes
In order to motivate and illustrate the power of the algorithm of orthogonalization and algebraic applications, this block is dedicated to the presentation of applications to engineering, such as water supply networks, although its application to other networks, such as of traffic, information, etc., is identical. It also includes applications to the problem of inclined planes with masses and pulleys, and electrical circuits.
An application of linear systems of inequalities. The water supply problem example
A linear programming example. Table manufacturing
How to obtain all solutions of linear programming problems
This block provides a series of standard exams with their solutions, to facilitate that the student can check if he has understood the material explained in the different topics of the course. Correspond to the type of exam that we have used at the University of Castilla-La Mancha for 20 years and that have been shown as very satisfactory.
Exam model 2015
Exam model 2016
Exam model 2017
In order to facilitate the use of the methods described in this course and students can work not only the exercises and problems raised, but other applications, we present here a computer application that implements the orthogonalization algorithm. Finally, a list of bibliographical references is given.
How to use the orthogonalization and the dual cone gamma algorithms
Bibliography
Examples of data files
Orthogonalization algorithm
Here are all slideshow from Algebra I
Slideshows