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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Given an LP problem how to transform the problem?

Given the following problem: $$ \max. -3x_1 -2x_2 - \frac{9}{2}$$ $$ \text{s.t.} -x_1 + x_2 \le 0$$ $$ 5x_1 + 3x_2 \le 8$$ $$ x_1,x_2 \ge 0 $$ When we convert the LP into standard form and then write down the simplex tableau we see that the…
moli
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If origin is not included in an LP problem how do we get a basic feasible solution?

Given the following constraints for an LP problem: \begin{align} x_1 + 2x_2 &\ge 4 \\ -3x_1 + 4x_2 &\ge 5 \\ 2x_1 + x_2 &\le 6 \\ x_1 , x_2 &\ge 0 \end{align} When I draw the feasible region I see the origin is not included. Since we can't get an…
moli
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Why is it that a 3x3 math puzzle can have no more than 5 unknowns?

I'm going through the Brillient.org Algebra 1 course, and I came across a problem that I don't think was well explained, and I'm hoping I can find more insight here. So this type of problem, for some background, has a numeric value on each of the…
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Is it possible to know if the feasible region is unbounded without drawing it?

Given the following set: $$ -x_1 + x_2 = 4$$ $$ x_1 - 2x_2 + x_3 <= 6 $$ $$ x_3 >= 1 $$ $$ x_1,x_2,x_3 >= 0 $$ Without drawing the feasible region can I know if it is bounded or unbounded?
moli
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solve the linear problem with graphic method.

\begin{equation} 2x_1 + 3x_2 \geq 6 \\-5x_1 + 9x_2 \leq 12 \\ 2x_1 - 3x_2 \leq 6 \\ x_1 + x_2 \leq 5 \\ 0 \leq x_1 \leq 4 \\ 0 \leq 2x_2 \leq 5 \\ \min z = -3x_1 - 2x_2 \end{equation} solve the linear problem with graphic method. I found this…
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Confusion with modelling shortest paths using linear programming

When looking around for formulating the shortest path problem as a LP I found this: https://www.cs.princeton.edu/~rs/AlgsDS07/22LinearProgramming.pdf At slide 39 they give an example example But in my eyes, this solution doesn't satisfy the…
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How to find the recession direction of a given system?

I have the set $S ⊂ R^6$ $$ \begin{align*} −&x_1 +x_2 +x_3 = 2\\ &x_1 +x_2 −x_4 = 1\\ &x_1 −6x_2 +x_5 = 3\\ −&2x_1 +x_2 +x_6 = 2\\ x_1 \geq 0, x_2 \geq 0, &x_3 \geq 0, x_4 \geq 0, x_5 \geq 0, x_6 \geq 0 \end{align*} $$ How do I know if $S$ is…
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Question regarding the convexity of sets

Let $S\subset \mathbb{R}^{n}\times \mathbb{R}$ and consider it’s projection onto $\mathbb{R}^n$, $S =\{ x\in \mathbb{R}^n\mid (x, y)\in S, y\in \mathbb{R}\}.$ Assuming $S$ is convex, prove that $S$ is convex. My question is how does one go about…
mojorisin
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Positve part and negative part of a real number

Let $a$ be a real number . The positive part of $a$, denoted by $a^+$ is given by expression $$a^+ = \text{if } a\geq 0 \text{ then $a$ else } 0$$ The negative part of $a$, denoted by $a^-$ is given by expression $$a^- = \text{if } a\geq 0 \text{…
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Must linear programming return a solution at the vertex of a polytope?

Let's assume we want to maximize $x_1+x_2$, satisfying $x_1+x_2 \leq 1, x_1 \geq 0, x_2 \geq 0$. Simplex algorithm is going to return $\vec{x}=(0, 1)$ or $\vec{x} =(1, 0)$. But is there some reason why an LP solver couldn't return $\vec{x}=(0.5,…
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Minimum and Maximum value

$1000$ gardeners wants to plant two types of flower. $900$ of them plants Roses and $500$ of them plants Dandelions. let $X$ be the minimum amount of gardeners which plants both flowers, and let $Y$ be the maximum amount of gardener which plants…
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Formulate LP models for the following optimization problems (do not try to solve the LP models):

Suppose the only foods in the world are the following: The last row imposes variety in our meals by having a limit on the number of servings/day for each of the six food types. If a satisfactory diet has to have at least 2000 kcal of energy, 55 g…
Heath
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find the range of a added parameter in linear programming problem remains the optimal solution

How can I find the range of an added parameter in the linear programming problem which preserve the original optimal solution remaining to be the optimal solution? such as: $$ Max \space\space\space 6x_1+x_2+\theta x_3 $$ $\theta$ is the added…
maopao
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How to interpret the following linear programing problem?

My problem is simple, if I have: $W = 8w_1 +24w_2$ restricted by: $2w_1-3w_2≥-5$ $-4w_1+3w_2≥-15$ $w_1, w_2≥0$ The simplex table is easy, just one iteration after multiplying the restrictions by $-1$ but I don't know what to say about the problem…
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Rei origami swans and giraffes, Linear Programming

Rei volunteers to bring origami swans and giraffes to sell at a charity crafts fair. It takes her three minutes to make a swan and six minutes to make a giraffe. She plans to sell the swans for $\$4$ dollars each and the giraffes for $\$6$ each. If…
Heath
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