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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Linear programming duality theorem

As far as I know, there are 2 versions of this theorem: 1) $\max \{xc^T: xA \le b, x \ge 0, x \in R^n\} = \min \{by^T: Ay^T \ge c^T, y \ge 0, y \in R^m\}$ 2) $\max \{xc^T: xA \ge b, x \in R^n\} = \min \{by^T: Ay^T = c^T, y \le 0, y \in R^m\}$ Can…
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Is this the most efficient way to rearrange a linear programming objective with an absolute for lpsolve?

If linear programming is to be used to solve an objective function which contains absolutes then the absolute terms have to be rewritten using extra values, for example, the trivial objective "minimise $\left| x_1 + x_2 \right|$"…
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Can someone explain this Linear Programming example's explanation?

Can anyone explain part c) to me from this explanation? I don't understand how the author gets: $x=\frac1b$ when $a>b$ and $x=\frac1a$ when $b>a$ Intuitively I don't see how x can be used in both of those equations. I tried drawing it but I don't…
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Solving linear Programming problem with simplex method.

I have tried this question but can't come up with a maximization answer. I am not certain where I am wrong but I think my equations have an issue, you can't take look at them below the question. The questions states, An investor has to invest in an…
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Set of optimal directions is a cone

Let $\vec{u}$ be an optimal point for the linear programming problem: \begin{equation} \min{ \vec{c}^T \vec{x}}\\ \text{s.t. } A\vec{x}=\vec{b} \text{ and } \vec{x} \geq \vec{0} \end{equation} where $A\in M_{m\times n}$, $\vec{c}\in\mathbb{R}^n$,…
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Show that Feasible Region of Linear Program is a Single Point

I have a set of variables $x_i$ for which $x_i \ge 0$, and a set of linear equations relating them: $A \mathbf{x} \le \mathbf{b} $. The typical constraints for a linear program. Is there a general way to check if the region of feasible solutions is…
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TRUE OR FALSE: A noncanonical linear programming problem with more unconstrained independent variables than constraints is unbounded.

I believe this is true because when we have unconstrained independent variables, we must pivot each one and file it in order to convert the tableau to canonical form. Now, if we have more columns than rows in a tableau, and we must pivot on each…
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Linear programming question: Sensitivity Analysis

I was given a problem where a home computer table sells for $36$ dollars and uses $6$ board ft of lumber, $2$ finishing hrs, and $2$ carpentry hrs. Should the company manufacture any home computer tables? Given LP: $\max$ $z$ = $60x_1$ + $30x_2$ +…
comp890
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Basic Feasible solution And Optimality condition

Maximize : z = $ x_1 + 2 x_2 - 3 x_3 + 4 x_4 $ subject to $ x_1 + x_2 + 2 x_3 +3 x_4 = 12$ $x_2 + 2 x_3 + x_4 = 8$ where $ x_1 , x_2 , x_3 , x_4 >= 0 $ I have calculated all the possible basic solution these are (0,0,3,2) and z =…
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Linearization of a max function

I have to cope with a constraint of the form (1) in the following problem: $$\begin{align}\max\quad& x+y\\ \text{s.t.}\quad& x + y \leq \max \{x,y\} &(1)\\ &0 \leq x \leq U_x&(2)\\ &0 \leq y \leq U_y&(3)\\ \end{align}$$ In the following link you…
Clement
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How to formula the given linear programming model?

Chem Labs uses raw materials I and II to produce two domestic cleaning solutions, A and B. The daily availabilities of raw materials I and II are 150 and 145 units, respectively. One unit of solution A consumes 0.5 unit of raw material I and 0.6…
Hamada
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changes on RHS of a constraint in LP

Question: What change in the RHS vector $b=(8,4)^T$ would increase on the optimal value of the objective function? Attempt: Suppose we change the first component of $b$, say now we have $b' = (k,4)$, the basis matrix $B = [ (1,-1)^T; (0,1)^T] $ …
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Changes in Primal and Dual Solutions When Scaled

Suppose that we have an LP in the standard form $$\text{(P) min }c^Tx: Ax=b, x\le 0$$ and it's dual would be $$\text{(D) max }b^Tx: Ax\le c$$ Let $\overline{x}$ and $\overline{y}$ be the optimal solutions to (P) and (D) respectively. How…
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how to express the following constraint for linear programming

I would like to express the following constraints mathematically: For a flow $f$ the sum of all the weights $w_{ij}$ of the edges for which $x^f_{i,j} \gt 0$ should be less than $W^f$. I apologize I am not able to express myself correctly, English…
Corey
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Farkas Lemma using duality

To Prove: $Ax =b, x \geq 0$, $ x\in \mathbb{R}^n$ has solution $\iff$ there is no $y \in \mathbb{R}^m$ (y is unrestricted in sign) such that $y^T A \leq 0 $ and $y^Tb > 0$. Attempt. We consider the following primal-dual \begin{align*} \max 0 x…
James
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