Questions tagged [linear-programming]

Questions on linear programming, the optimization of a linear function subject to linear constraints.

A linear programming problem may be defined as the problem of maximizing or minimizing a linear function subject to linear constraints. The constraints may be equalities or inequalities.

Linear programs are problems that can be expressed in canonical form as \begin{align}\max\quad&c^\top x\\\text{s.t.}\quad& Ax\le b\\\quad& x\ge 0\end{align} where $x$ represents the vector of variables (to be determined), $c$ and $b$ are vectors of (known) coefficients, $A$ is a (known) matrix of coefficients, and ${\displaystyle (\cdot )^{\top}}$ is the matrix transpose.

The expression to be maximized or minimized is called the objective function ($c^{\top}x$ in this case).

The inequalities $Ax \le b$ and $x \ge 0$ are the constraints which specify a convex polytope over which the objective function is to be optimized. The inequality $x \ge 0$ is called non-negativity constraints and are often found in linear programming problems. The other inequality $Ax \le b$ is called the main constraints.

Applications:

Linear programming can be applied to various fields of study. It is widely used in mathematics, and to a lesser extent in business, economics, and for some engineering problems. Industries that use linear programming models include transportation, energy, telecommunications, and manufacturing. It has proven useful in modeling diverse types of problems in planning, routing, scheduling, assignment, and design.

References:

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Is this linear programming problem right?

The problem is: Beth works a maximum of 20 hours/week programming computers and tutoring math. She receives 25 dollars/hour for programming and 20 dollars/hour for tutoring. She works between 3 and 8 hours/week programming, but always gives more…
Someone
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Convert problem to linear programming task

I have function $\max \{ |x-1| + 2|y-1| | x,y \in R, x+y \leq 2 \}$. Can this problem be converted to LP? I think it cant because of the abs. value in criterial function, but Im not sure. If it can, how to convert it? I think that restrictive…
Smajl
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Looking for Miller Tucker Zemlin (MTZ) constraints example

I need your help. I am working on Travelling Salesman Problem. In that problem I have these constraints: $ \sum\limits_{j=1}^{n} X_{ij} = 1$ , $ i=1,2, ...,n$ $ \sum\limits_{i=1}^{n} X_{ij} = 1 $ , $j=1,2, ...,n$ $X_{ij} \in \{0,1\}$, $X_{ij}=1$…
lauzi
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Check if two rectangles (do not) overlap in a Integer Linear Program

A rectangle $i$ can be represented by a tuple $(x_i, y_i, w_i,h_i)$ where $x_i$ is the bottom left $x$-coordinate of rectangle $i$; $y_i$ is the bottom left $y$-coordinate of rectangle $i$; $w_i$ is the width of rectangle $i$; $h_i$ is the height…
Auberon
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Determine if this set is a polyhedron or not

Recently I have encountered this set, from "Introduction to Linear Optimization" by D. Bertsimas and John.N.Tsitsiklis: $$P = \{(x,y) \in \mathbb{R}^2 : x \cos \theta + y \sin \theta \le 1, \forall \theta \in [0; \pi/2 ] \wedge x \ge 0 \wedge y \ge…
ElementX
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showing a set of solutions is convex.

I have already shown that the set of all feasible solutions of the LP $ \min \{ cx : Ax = b , x \geq 0 \}$ is convex. Now, Im asked to show that the set of all optimal solutions to this LP is convex as well. But, how can I express the set all of…
ILoveMath
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Cannot understand why do we need to split $x$ variables into $x^+$ and $x^-$ in Linear Programming

In this video MIT professor says that you need to split $x$ into $x^+$ and $x^-$ such that $x = x^+ - x^-$ (at 53:42) to convert any LP to standard form. Standard LP form is: $max \ c^Tx$ $Ax = b$ $x \geq 0$ It does not make any sense to me. I do…
YohanRoth
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Proof of equivalence between definitions of adjacent vertices

In a lecture on the subject of linear-programming we were given 2 definitions for adjacent vertices. Let $P \subseteq \mathbb R^n$ be a polyhedron, and $\vec x, \vec y \in P$, then: (1) $\vec x$, $\vec y$ are adjacent vertices if they have $n−1$…
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If ratio test is not unique, can we conclude that the basic feasible solution after pivoting is degenerate?

Assume that you are solving a LP using Simplex method. You reach a point and know that at this point, $x_j$ (one of the decision variables) should leave the basis. So, you perform a ratio test to see which variable should enter the basis and fill…
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How to find linear programming constraints given a 2 player zero sum matrix

Given a problem like the following: A startup want to build talking washing machines spending the least possible. There are three ways of building them: manually, semi-automatically and automatically. The manual production demands 1 minute of…
UBears
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Linear programming: infinite solutions

This question has infinitely many solutions, how do we get to that conclusion? I used graph to solve it but it gave me single answer. Any help will be highly appreciated!
user405925
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Are my constraints linear?

I wrote different constraints for a problem and some people say that these constraints are not-linear. My own feeling is that my constraints are linear. Can you help me to prove that? My first constraint: $$ \sum_{i=1}^{g} \prod_{k=1}^{n} X_{ijk} =…
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Method to convert a worded problem to a linear problem

Acme manufacturing company has contracted to deliver home windows over the next $6$ months. The demands for each month are $100, 250, 190, 140, 220,$ and $110$ units, respectively. Production cost per window varies from month to month depending on…
UniStuffz
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Transforming a worded problem into a Linear Problem system of equation

(Advertising problem) Show & Sell can advertise its products on local radio and television (TV). The advertising budget is limited to $£10,000$ a month. Each minute of radio advertising costs $£15$ and each minute of TV commercials $£300$. Show &…
UniStuffz
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Prove that Minimum Vertex Cover problem is dual to Maximum matching problems

So, I'm able to formulate both linear programming problems like this: I have a graph G ={V,E}. Minimum Vertex Cover: $$ min \sum_{v \in V} x_v\\ x_{v_i} + x_{v_j} \geq 1, (\forall e = (v_i, v_j) \in E)\\ x_v \in \left\{0;1\right\} $$ where $x_{v_i}…
Eenoku
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