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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Dual problemn -> what to do with summand in objective function not connected to variable

say I have the simple primal problem $$ \text{max } Z = 3x_1 + 2x_2 -7 $$ s.t. \begin{align*} 3x_1 + 5x_2 &\ge 6 \\ 7x_1 + 55 x_2 &\ge 44 \\ x_1,x_2 &\ge 0 \end{align*} Now would I be able to use the summand $-7$ is the dual problem? Where does it…
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Represent point (20,10) as a convex combination of the LP’s bfs.

I am having difficulty understanding how you represent a specific point and write it as a convex combination of the linear programming bfs. According to an example found in operations research textbook, it gives an example where you represent a…
comp890
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Why do we only solve linear programming with equality constraints but not inequality?

I only see people deal with linear programming by converting it to standard form and solve using simplex algorithm. My question is why we stay focused on equality constraints rather than inequality ones while tackling linear programming?
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how to express big-M formulation as an indicator constraint

I want to solve the following LP using CPLEX. In the CPLEX documentation it is suggested to use indicator constraint instead of big-M formulation. I searched on google the term "indicator constraints" but except some research papers I could not find…
Corey
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Formulate model

Carter Enterprises is a soybean trading company. Once a month a representative attends a commodity sale where he either buys or sells soybeans in bulk. Carter uses a local warehouse for storing soybean inventory. The warehouse charges $\$10$ per…
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Just formulate linear program

A company produces fragrances $A$, $B,$ and $C$. There is virtually unlimited market demand for these. Fragrance $A$ sells for \$$10$ per gallon, $B$ for $\$56$ per gallon, and $C$ for $\$100$ per gallon. Producing $1$ gallon of $A$ requires $1$…
AQEEL
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My result doesn't agree with results from online calculators

I'm doing an exercise about linear programming, but my answer doesn't agree with the answer from online calculators like this and this. Below is the problem statement: $$Minimize: u = 4x - 3y, s.t.$$ $$y \le -x + 1$$ $$y \le x + 1$$ $$y \ge 0$$ I…
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Linear Programming - Creating a sequence

I have some numbers in an array and i want to model a LP problem that generates the absolute sequence of the numbers (according to their growing order). For example input [4,2,1,5] ---> output [3,2,1,4] That is,if i sort [4,2,1,5], 4 has the third…
Jhdoe
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Followup Question: Linear Programming - Preventing Staff Scheduling Shift Overlap?

I am trying to understand part of the methematical model and answer posted in the following question: Linear Programming - Preventing Staff Scheduling Shift Overlap? My question is concerning @Erwin Kalvelagen answer. The M is just a constant e.g.…
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Write the dual for the following linear program

Write the dual for the following linear program: max($3x_1 + 8x_2$) subject to $x_1 + 4x_2$ ≤ 20 $x_1 + x_2$ ≥ 7 $x_1$ ≥ -1 $x_1$ ≤ 5 The posted solution is as follows, but does not show the steps. Where did I go wrong?
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finding optimal solution of a min network flow problem

We have the following the min cost network flow problem. Notice that the arcs $(1,2), (2,3), (4,2), (3,6), (5,6)$ give a feasible basis. We easily find a feasible solution: $$ (x_{12}, x_{23}, x_{36}, x_{42}, x_{56}) = (-6,-1,-1,-3,-1) $$ where…
James
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How many boxes of each mixture should the company make to maximize profit? Linear Programming Problem

A company makes two snack mixtures. A box of mixture A contains 6 ounces of peanuts, 1 ounce of M&M's, and 4 ounces of raisins and sells for \$4.25. A box of mixture B contains 12 ounces of peanuts, 3 ounces of M&M's, and 2 ounces of raisins…
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Linear Programming Word Problem: Theater

I'm having trouble understanding the second constraint. A theater is presenting a program on drinking and driving for students and their parents[...] admission is 2.00 dollars for parents and 1.00 dollar for students. However, the situation has…
Slecker
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What is the dual for the following LP

Minimize $c^Tx$ subject to, $b_l \leq Ax \leq b_u \\ l\leq x \leq u$ where $A$ is an $m \times n$ matrix. My approach was to separate each inequality into two. So, $b_l \leq Ax\\ Ax\leq b_u\\ l\leq x\\ x\leq u$ And the dual objective would then…
user88923
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Changes to LP if a new constraint is added

Applying simplex, I found out the optimal solution to be $z^*=16$ and $x^{*} = (8,0,0,0,12)$ where $x_4,x_5$ are slack variables. Now, suppose we add constraint $x_2+2x_3 = 3$ So, If I were to add this constraint to the optimal tableau, we see that…