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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Formulating a pipeline with several variables

The question I have one constraint as number of faculty signing a contract of length r, i am unsure what other constraints i can make to complete the program. Would it be the amount of years worked?
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Find the largest $\epsilon$ for any $0\le t\le \epsilon$ s.t. $\vec x^*$ is still optimal to the given LP

Maximize $\vec c*\vec x$ subject to $A\vec x\le \vec b$ and $\vec x \ge \vec 0$ $\vec c$=$\begin{bmatrix}1 \\2\\1\end{bmatrix}$, $\vec x$=$\begin{bmatrix}x_1 \\x_2\\x_2\end{bmatrix}$ A=$\begin{bmatrix} 1 & 1 & 1 \\\ -2 & -2 & 1 \\\ 0 & -1 & -1…
user8714896
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Is this a linear constraint?

I'm wondering, is the following a linear constraint $$x + ry \geq 12 , \quad r \in [2, 3]$$ $$x,y \in {\rm I\!R}$$ I don't think it is, because it's not defined everywhere where x and y are. If that condition for r was not there, then it would be…
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Formulate a linear program to minimise the total salary paid to professors making sure they sign up each year

This link is an image of the question: The Dean of Physical and Mathematical Sciences of ABX University is drawing up her plan for the full time professor needs for the next four years. After looking at the projected total credit hours offered in…
jon doe
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Geometry of complementary slackness

Can someone help me understand what's going on in these notes? I don't understand what $e_j$ is supposed to be. How it $\alpha_1$ supposed to be orthogonal to $x_j$? Isn't $\alpha_1$ just a constraint in the primal?
Gooby
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Using binary variables to linearize a non-linear constraint in LPP

I have a constraint that makes the optimization problem nonlinear. The constraint of interest is: If (a-b)>=0 then c=(a-b) else c=0 where $a$, $b$ and $c$ are variables. How to linearize this constraint to convert the problem to linear…
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Nested Linear Program

I have a linear program: minimise $f^T x$ with equality and inequality constraints. This does not have a unique solution, so I would like to find the solution of this that also minimises $g^T x$. One approach to doing this is to solve a second…
mikado
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LP: multiple optimal solutions, unbounded, infeasible?

I'd like to ask the following question(s), to help me de-confuse things: $5y + x \geq 7$ $-3y + 4x \geq 5$ $4y - x \leq 15$ $y - 3x \geq -21$ $y - 4x \leq 42$ Given these constraints, what could be an objective function for which the LP has…
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How to reformulate this optimization problem as a linear program?

Let $Ax \leq b$, $x \geq 0$ define the feasible region. Each constraint defines a hyperplane in $R^n$ and the distance from a point $\hat x$ to a hyperplane is $d_i(\hat x)$ = $(b_i - A_{i,*} \hat x)$ / $|| A_{i,*} ||$ with $|| A_{i,*} ||$…
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Converting minimizing wasted string when partitioning 200cm into 90,70 and 50cm to Linear Programming problem

Say you have 3 products that require x amount of string to make: Product A: requires 90 cm of string Product B: requires 70 cm of string Product C: requires 50 cm of string String comes to you from your suppler in sizes of 200 cm only. You get a…
Gooby
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Feasible region unbounded

How do we prove that if a linear programming problem is unbounded, then its feasible region is necessarily an unbounded set as well? It kind of seems intuitive but how do I rigorously show this?
sedrick
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How did they get the standard form of this LP?

I'm confused to what method they are using to get the standard form of this LP? Why is there an "e" variable? I need help with this problem.
user616370
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Linear programming problem's primal seems to contradict its dual

Given $A\in\mathbb{R}^{m\times n},\ B\in\mathbb{R}^{m\times m}, c\in\mathbb{R}^n, b, d\in\mathbb{R}^m$, $B$ nonsingular, I've been tasked with solving the following LP problem (denoted (P)): $$ \max_{x,u} c^\top x + d^\top u \\ \text{s.t. }\ Ax + Bu…
user3002473
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What is the proof for boundedness of the following LP problem?

\begin{array}{ll} \text{maximize} & Ax + By \\ \text{subject to}& Cz + Dw = 1 \\ & A’x + B’y \le C’z + D’w \\ &x, y, z, w \ge 0. \end{array} where A, B, C, D, A’, B’, C’, D’ are constant positive 1×n matrix and x, y, z, w are n×1 matrix. What is…
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Method of determining the correct side

In Linear Programming, we use the “origin side” method to determine which side is the “>” side of the straight line $f(x, y) = 0$. I know it is NOT necessary true that $f(x, y) > 0$ is always on the “right hand side” of $f(x, y) = 0$. But it seems…
Mick
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