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
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finding the requirement space and feasibility of a LP problem

Attempt: Let $x_5,x_6$ be slack variables so our system now looks like \begin{align*} \max \; \; \; & -x_1 - x_2 + 2 x_3 + x_4 \\ \text{subject to} \; \; \; & 2x_1 + x_2 + x_3 + x_4 - x_5 = 6 \\ & x_1 + 2…
James
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Modeling a problem as a linear programming problem

Attempt Let $x_{ij}$ be the amount of money we invest for a period of $j$ months. We want to maximize the total cash at end of month 4 (or beginning of month 5). We have that objective function is $$ z = 1.001 x_{11} + 1.005 x_{12} + 1.01 x_{13} +…
James
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Why do we introduce artificial variable in two phase simplex method?

In two phase simplex method we use artificial variables when our constraint is greater than or equal to some constant. I just want to know what is the purpose of these artificial variables?
Shariq
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Proving the existence of a solution to an LP

I'm working on the following exercise: Let $c \in \mathbb{R}^n$ and $A \in \mathbb{R}^{m*n}$. For an any arbitrary $b \in \mathbb{R}^m$ we consider the following problem $(P_b)$: $$min_{x \in \mathbb{R}^n} c^Tx$$ $$\text{such that } Ax = b, x \ge…
3nondatur
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Can a non-degenerate LP have multiple optimal solutions?

In linear programming, an LP can have multiple optimal solutions if it contains degenerate vertices, i.e. where one of the base-variables is 0. Can an LP also have multiple optimal solutions if it does not contain degenerate solutions? If so, what…
dtech
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Degenerate solution in linear programming

How can I determine if a solution in a linear programming problem is degenerate without I use any software or the graphical display of the solution; For example in the model: $$\max\{2x_1 + 4x_2\}\\\phantom{ aa}\\ …
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Sensitivity analysis in linear programming

Could someone please explain in detailed steps how to apply a sensitivity analysis to such problem: $$maximize \ \ 2x_1 + 3x_2 \\ s.t. \ \ 4x_1+3x_2≤600 \\ 2x_1+2x_2≤320 \\ 3x_1+7x_2≤840 \\ x_i≥0$$ The goal is it to determine the boundaries of…
Bastian
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When to use which simplex algorithm?

in linear programming we use simplex method to find optimal solution. But I have also seen methods like Two Phase Method, Dual method, M-method. My question is, how do I know which method to use? For example when do I use two phase method?
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Linear Programming with target values.

I'm trying to figure out the general solution to a min-max problem. The general form of the problem is as follows: x1 + x2 + ... + xn = T a1x2 + a2x2 + ... + anxn = At * T x1 >= 0 x1 <= T1 …
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A linear program for maximizing a fraction

Given $\lambda_1,\ldots,\lambda_n \geq 0$ and an $n\times n$ matrix $A$, I wish to maximize the ratio $$ \frac{\lambda_1x_1 + \cdots + \lambda_nx_n}{x_1+\cdots+x_n}, $$ where $x_1,\ldots,x_n \geq 0$ are not all zero and $A\mathbf{x} \leq \mathbf{0}$…
Hubble
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How to show a primal program is unbounded by using weak duality?

In weak duality theorem, we assume $x_i$ and $y_i$ are feasible. But how could we show a primal program is unbounded by this theorem? Suppose we have a primal program: $\max \mathbf c^\top \mathbf x, \mathbf A\mathbf x \leq \mathbf b, \mathbf x \geq…
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Convert the non linear problem into standard minimization linear programming form

I have to convert the non linear problem into standard minimization linear programming form Minimize: $|x|+|y|+|v|$ Subject to: $$x+y\le1$$ $$2x+v=3$$ I dont have any idea how can I do it...I would appreciate any help.
luka5z
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Dual problem of a maximization primal problem $P$?

Suppose we have a primal problem $P$ which is stated as a maximization problem $\max c^{T} x$. The dual problem is defined (Introduction to Linear Optimization by Dimitris Bertsimas) only for a primal minimization problem. Then what is the dual…
Shuzheng
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Linear programming: Basic solution

Let $P = \{ x \in R^n : Ax \leq b, x\geq 0\}$ and $Q= \{ (x, r)' \in R^{n+m}: Ax + r= b, x \geq 0, r\geq 0\}.$ Show that $$x \text{ is basic solution of } P \iff (x, b-Ax) \text{ is basic solution of }Q$$ Type: The restrictions in Q are associated…
Giiovanna
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What constraints are needed to to switch on a binary variable in a linear programming model?

I am trying to create a binary variable ($z$) within a linear model which 'switches' on only when another variable ($d$) becomes greater than zero. I have had some success using the following two constraints (where $M_l$ and $M_u$ are lower and…