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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Drawing in 3 dimensions: Feasible region

We have the following constraints: $$ 0 \leq x \leq 10$$ $$ 0 \leq y \leq 20$$ $$ 0 \leq z \leq 25$$ $$ 0 \leq x + y + z \leq 15$$ We have to draw this in an 0xyz - coordinate system, I did the following, I don't know if it's correct: Mainly the…
Ylyk Coitus
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Linear Programming Price Change After X Units Sold

I have a question regarding writing some formulas for LP. How would you code the price change after X number of units sold. So lest say the base price for the first X units sold is £5 and then there is a £1 discount for units bought after the X…
FrosT
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Find average value of the function $f(x,y,z)=3x-4y+5z$ over the triangle (simplex) $x+y+z=1$ ($0\leq x,y,z<1$).

Find the average value of the function $$f(x,y,z) = 3x-4y+5z$$ over the triangle (simplex) $\left\{ (x,y,z) \mid x+y+z=1 \land 0 \leq x,y,z < 1 \right\}$. Is there a simple way to do this problem?
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Verify that the optimal basis consists of the particular slack variable without using simplex method.

In a linear programming problem, how to verify that the optimal basis consists of the slack variable of a particular constraint without using the simplex method? Consider the following problem: $$ {\rm Maximize} 10x_1+15x_2+5x_3$$ subject to…
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How to prove that $c^Tx(\mu)$ is strictly decreasing with $\mu$ in interior point method for LP

Consider the Primal-Dual problem, (P)min $c^Tx$ s.t. Ax = b, x $\geq 0$ (D) max $b^Ty$ s.t. $A^Ty + s = c$, s $\geq 0$ The log-barrier function for (P) is : min $c^Tx - \mu \sum_{i=1}^n ln(x_i)$ s.t. Ax = b, x > 0 How to prove that if $\mu >…
Icy
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How can I reformulate the problem in terms of convex combinations of the extreme points?

Maximize $$ x_1 + 2x_2$$ \begin{align} x_1 - 4x_2 &\le 4 \\ -2x_1 + x_2 &\le 2 \\ -3x_1 + 4x_2&\le 12 \\ 2x_1 + x_2 &\le 8 \end{align} Identify all the extreme points and reformulate the problem in terms of…
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Find all the optimal solutions to the dual problem of this maximization problem

This was posted a year ago, but no answer was posted. Here's my crack at it and hopefully I can get some critique because I want to get better at this. Maximize…
user8714896
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linear programming issue

Hi I need help regarding a linear programming math problem. What I need is to formulate the equations. I tried this. But no idea whether the equations are correct. What I need to know is whether my following decisions are correct. Let's assume…
Hiru
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Write the min-max model in the standard LP form

I was given two linear systems {$2x=1$, $x=1$} and I was told to write the min-max model. Which I hope I did correctly and got $|| Ax-b||$ = max {$||2x-1||, ||x-1||$} -> min. now it is asking me to write the min-max model in the standard LP form as…
Hidaw
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How to tell if linear programming dictionary is unbounded using ratios?

I don't really get how they got negative for the ratio 2/5. Is it because if they make $x3$ a leaving variable it'll become $x3$ = -5/2 + (3/2)$x1$? How does non-positive ratios make a problem unbounded?
Gooby
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finding coefficient of "Max Z = $ax_1 + bx_2 + cx_3 + dx_4 + ex_5$" given a similar constraint?

I was given a primal problem as follows: Max Z = $ax_1 + bx_2 + cx_3 + dx_4 + ex_5$ Subject To: $a_1x_1 + b_1x_2 + c_1x_3 + d_1x_4 + e_1x_5 \geq F$ $a_2x_1 + b_2x_2 + c_2x_3 + d_2x_4 + e_2x_5\geq G$ And also given the final iteration as…
Meira
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LP Problem Formulating

Gotham Motor Oil Company has three warehouses which it can ship products to its three retail outlets. The demand in cans for the product Super Blend is 100 at retail outlet 1; 250 at outlet 2; and 150 at outlet 3. The inventory of this product at…
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Simplex Method with Nontrivial Initial Solution

I have a linear program with the following tableaux: \begin{array}{crrrrrr|l} & x_1 & x_2 & s_1 & s_2 & s_3 & P & rhs \\ \hline & 67& 126& 52& 36& -7& 0& 988\\ & -24& -46& -19& -14& 3&…
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Infeasible solution in Duality and Dual simplex method

Currently I am preparing the Linear Programming exam and I've got some issue to solve these problems. Shortly, suppose some linear program: max $C^{T}X$ s.t. $AX \leq b$, where $A$ is $2 \times 3$ matrix. After adding slack variables $x_4$and $x_5$…
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Linear program with absolute values in the objective

I know that if there is a absolute values in Linear Programming problem, i.e. $min \sum_{i} c_i|x_i|$ s.t $Ax \leq b, x \geq 0$ > then, I can change $|x_i|$ into new variables such as $|x_i| = x^{+}_i + x^{-}_i$ s.t. $x^{+}_i , x^{-}_i \geq…