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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Integer and continuous constraints in a linear programming problem

Until now i formulated some Linear Programming problems with integer constraints and some with continuous constraints. Now, i've written a linear programming model that both contains variables with integer constraints and with continuous…
Koinos
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Linear programming, variable without non-negativity constraint

In a linear programming problem where we have a variable $x_k$ which has no non-negativity constraint, we can replace it by $x_k = u_k - v_k$, where both $u_k$ and $v_k$ have to be $\ge 0$. Can there exist a basic feasible solution where both $u_k$…
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From where bounds on $x$ came?

Suppose we have linear programming problem: \begin{align*} \underset{x_1, x_2}{\operatorname{minimize}}\quad& c_1x_1+c_2x_2\\ \mbox{s.t.}\quad&a_{i1}x_1+a_{i2}x_2 \ge \beta_i\quad& (i = 1,\dots,n). \end{align*} How do we get bounds on $x$ in its…
Yola
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Linear Programming Simplex Method: How to pick leaving variable

I hope someone can help me. I am trying to get a head start on uni this year by learning some linear programming from a book, but it is getting confusing. I have read that you pick the leaving variable by minimising the ratio $\{\frac{b_i}{a_{ij}}…
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Absolute value in Linear programming problem

I have this problem, where I have to reformulate it as a linear programming problem. Minimize $ 2x_1 +3 \vert {x_2-10}\vert $ subject to $\vert {x_1+2}\vert + \vert {x_2}\vert ≤5 $ The subject is new to me. Can anyone help?
Gabarta123
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Show that $\alpha_{1}x+\alpha_{2}y\geq \beta$ holds true for all points in $P\Longleftrightarrow$ the inequality is true for all extreme points in $P$

Given a polyhedron, $P\subset \mathbb{R}^2$, I am to show that the inequality $\alpha_{1}x+\alpha_{2}y\geq \beta$ holds true for all $\binom{x}{y}\in P$, if and only if the inequality holds true for all extreme points in $P$. The first part is…
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Formulating a problem as linear programming optimization problem

Attempt: Let $x_{INi}$ be the number of people who travel from Ithaca to Newark in class $i$ where $i=1,2,3$ where each number represents class Y,B, and M, respectively, by simplicity. Similarly, write $x_{NBi}$ and $x_{IBi}$. Our goal is to…
James
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Why is my linear programming model wrong?

(Investment problem) An individual wishes to invest £5000 over the next yearin two types of investments: Investment A yields 5% and investment B yields 8%. Market research recommends an allocation of at least 25% in A and at most 50% in B.Moreover,…
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Is the canonical form of LP programs unambiguous?

Is the canonical form of LP programs unambiguous? Because oddly I've seen some notes describe the canonical form as replacing $\leq$ constraints with $=$. While some other notes said that canonical forms "only have $\leq$ constraints". So what's the…
mavavilj
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Transportation algorithm

I am attempting Q17 on this worksheet: http://www.statslab.cam.ac.uk/~qb204/teaching/ex_optim_2.pdf Am i correct in reformulating the problem as : minimise $\sum_{i=1}^{n} \sum_{j=1}^{n} tij $ ? But I don't understand what constraints there need to…
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Linear and Integer Programming

How many different solutions are there to the equation $x_{1}+x_{2}+x_{3}+x_{4}+x_{5}+x_{6}=16$ with the following constraints: $x_{1}\geq 1$ $x_{2}\geq 2$ $x_{3}\geq 0$ $x_{4}\geq 3$ $x_{5}\geq 2$ $0\leq x_{6}\leq 1$ So far, how I've been…
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Number of equations and variables in a Linear Programming problem

Why in every Linear Programming problem in standard form it's assumed that $m\leq n$ (where m are the rows and n the columns of the A matrix) ? Thanks
Koinos
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Linear Programming problem with 3 variables for factory production.

A firm produces three different types of finished material in which to construct shoes, canvas and rubber. Each of these materials requires the following amounts of production (in hours) to produce $\bbox[yellow]{100 }\,$square yards in three…
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Linear Programming Confusion about Complexity

In the wiki page of Linear Programming is told that Linear Programming problems belong to P complexity class. However, the method generally used to solve Linear Programming problems is the Simplex method that not belong to P. So, does this make…
Koinos
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Effect of adding linear inequalities on the solution space of a optimization problem?

In linear optimization, I often see linear inequalities that define the solution space being added up. Obviously if $1 < 4$ and $9 < 10$ then also $1 + 9 < 4 + 10$, so adding up both inequalities does not seem to do much harm (if you're adding up…
WBM
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