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:

5084 questions
0
votes
2 answers

Linear Program to find line that best fits a set of points

Given a set of points $(x1,y1),(x2,y2),...,(xn,yn)$ the following is supposed to be a linear program that finds a line$ $ax+by=c that minimizes $max|ax_i+by_i-c|$. Let $z=max|ax_i+by_i-c|$ This implies $z\ge|ax_i+by_i-c|$ or $-z\le ax_i+by_i-c\le…
user137481
  • 2,605
0
votes
1 answer

Solving an LP problem with an upper limit for the variables

Im trying to solve the Above LP. Now, can we apply just simplex considering that we can treat the upper bounds of the variables as constraints. Meaning, we need to add $6$ slack variables, and it would be a bit harder to do the algorithm by hand.…
James
  • 3,997
0
votes
0 answers

Assign least upper bound to variable for piecewise linear function in Linear Programming

Here I am trying to calculate the US capital gains tax $(cgt)$ using a piecewise linear function, $f(x) = max(f1(x), f2(x), f3(x)))$. One sub-function for each of the tax brackets. US tax law defines the low bracket value as starting with the amount…
0
votes
2 answers

If else statement in Linear programming with same variable?

Is it possible to write the following if else condition in Linear Programming with big M method? "if $x < 1$ then $x = 0$". "$x$" is a positive variable. PS: This is part of a bigger optimization problem where "x" should only appear if this is…
SEMV09
  • 3
0
votes
1 answer

Trying to set up a linear programming problem

Attempt Let $x_1$ be the number of hours to produce product 1 during assembly and $x_2$ be the number of hours to produce product 1 during finishing. Notice that $\frac{1}{2} x_1 + x_2 $ is the number of product 1 units produced. Similarly, call…
0
votes
1 answer

Proving an optimal solution to an LP also is optimal for a modified one

Consider the LP $\min cx $ subject to $a^i x = b_i $ $i=1,...,m$ and $x \geq0$ where $x$ is an n-vector. Let $x^*$ be an optimal solution to this LP. Let $\pi^*$ be the optimal solution to the dual. Prove that $x^*$ is also optimal…
0
votes
1 answer

Solving Linear program by the dual simplex method

I have this LP: Maximize $ 2x_1 + 3x_2$ S.t (1) $ 2x_1 + 2x_2 \leq 30 $ (2) $x_1 + 2x_2 \geq 10$ (3) $ x_1, x_2 \geq0 $ I have to solve the LP by using the dual simplex method, and I have to start with the basis consisting of the…
Gabarta123
  • 59
  • 1
  • 4
0
votes
1 answer

Converting to standard form - at basic solutions, at least one of the two positive variables that replaces a free variable should be zero. Why?

My linear optimization note says the following about handling free variables (variables that are not restricted to be non-negative) when converting a linear problem into the standard form: The method to deal with free variables is to replace them…
0
votes
1 answer

Basic Feasible Solutions, Basic Solutions and Optimal Solution

I'm currently studying linear programming and I came across this MIT resource. In the very first page of the pdf, under BT Exercise 2.10 the 6th statement reads: Consider the problem of minimizing max{c’x, d’x } over the set P. If this problem…
PPGoodMan
  • 297
0
votes
1 answer

Is the set of basic feasible solution, $P=\{x\in\mathbb{R}^n|Ax=b,x\ge0\}$, nonempty?

Has the subset of $\mathbb{R}$, defined as $P=\{x\in\mathbb{R}^n|Ax=b,x\ge0\}$, a basic feasible solution? I think that no, because maybe P=$\emptyset$, so an empty polyhedron does not have basic solution. Am I wrong? In the case $P\neq\emptyset$,…
Gibbs
  • 544
0
votes
1 answer

Variable as an index in linear programming

Is it possible to use a variable as an index in linear programming ? For example $\sum_{t=y}^{C}x_{t}= a$ where y is a variable (and also $x_{t}$; C and a are constants)
Koinos
  • 191
0
votes
0 answers

About the proof of a theorem about Linear Programming in C. L . Liu "Introduction to Combinatorial Mathematics"

I am reading C. L . Liu "Introduction to Combinatorial Mathematics". I think his proof of the following theorem is not correct. Am I right? p.312 Theorem 12-1 If a linear programming problem has a feasible solution, it also has a basic feasible…
tchappy ha
  • 8,690
0
votes
0 answers

Finding the dual of an LP

For the first part, Once I pivot and make $x_4,x_5$ enter the basis, we can obtain our original problem. Actually, -35 should be -62 so that we get $$ min z = 6x_1 + 20 x_3 $$ such that $$ x_2 + 4 x_3 \leq 10 $$ $$ 30x_1 - x_2 + 2 x_3 \leq 11…
0
votes
1 answer

Interpretation of a restriction of a linear programming problem

I'm trying to model the number of new planes an airline must buy. There are 3 types: small, medium and big. Let $x_i$ be the number of new planes of type $i$ that the airline buys (1=small, 2=medium and 3=big). One of the restrictions of the…
0
votes
0 answers

Stuck with a Integer Programming problem

I've tried hours and hours to model this problem but i didn't succeed. Can you help me ? We want to realize n projects in the next T years. For each project, a profitability index pi is known, which expresses the expected final gain (in Euro) and…
Koinos
  • 191