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
1
vote
1 answer

Modifying primal constraint in a LP problem

Suppose we have a primal-dual pair in standard form, Add a scalar multiple of one primal constraint to another primal constraint. Does this change the dual solution? Try Supose we have primal $ \max cx $ subjeect to $Ax = b $, $x \geq 0$ and the…
James
  • 3,997
1
vote
1 answer

multiplication of nonzero scalar in a constraint of the primal

Suppose we have primal and its dual in standard form, that is \begin{align*} (P) \max z = cx \\ st \; \; Ax = b \\ \; \; \; x \geq 0 \\ \end{align*} \begin{align*} (D) \min z = by \\ st \; \; yA \geq c \\ \; \; \; y \; \; \; free…
1
vote
1 answer

Formulating a LP minimization problem

Attempt Let $x_i$ be the number of workers to be hired that starts its shift on day $i$. So we want to minimize the function $f( {\bf } ) = \sum_{i=1}^7 x_i$. The constraints: $$ x_1 \leq 17 $$ $$ x_1 + x_2 \leq 13 $$ $$ x_1 + x_2 + x_3 \leq 15…
James
  • 3,997
1
vote
0 answers

Solution to a primal LP relation to the dual

Suppose we have the following LP \begin{align*} \min z = x_1 + 2x_2 \\ x_1 \geq 1 \\ x_1+x_2 \geq 2 \\ x_1,x_2 \geq 0 \\ \end{align*} We can use simplex or a graphical method to find the optimal solution which is $2$. and the optimal feasile…
1
vote
1 answer

Finding the dual of a linear programming problem

Consider the LP $min f(x_1,...,x_n) = \sum_{i=1}^n i x_i $ such that \begin{align*} x_1 \geq 1 \\ x_1 + x_2 \geq 2 \\ ... \\ x_1 + ... + x_n \geq n \end{align*} Im trying to find the Dual and an optimal solution to the LP attempt The dual is…
James
  • 3,997
1
vote
1 answer

Finding degenerate and nondegenerate BFS

Consider the Linear programming problem $$ maximize \; \; \; z = x_1 + 2x_2+ 3 x_3 $$ subject to \begin{align*} x_1+x_2+2x_3 & \leq 4 \\ x_1 &\leq 4 \\ x_i &\geq 0 \end{align*} Find a nondegenerate basic feasible solution, a degenerate BFS, and…
1
vote
1 answer

Suppose that for a certain LP no basic feasible solution is degenerate. Does it follow that this LP has a unique optimal solution?

I was wondering if the following is true. Suppose that for a certain LP no basic feasible solution is degenerate. Does it follow that this LP has a unique optimal solution?
1
vote
1 answer

Deciding whether a LP problem has an optimal solution

We have an LP problem with 4 extreme points $x_i$, $i=1,2,3,4$ and 4 extreme directions $d_i$ with objective function with coefficients given by vector $c$ such that $c^T x_1 = 7, c^T x_2 = 12, c^Tx_3 = 8, c^Tx_4 = 10$ and $c^Td_1 = -5 $,…
James
  • 3,997
1
vote
0 answers

Simplex method: Why tableau row operation produces correct indicator vector?

I learned the objective variable can be written as: $$ z = c_B^T \bar{b} - \xi^Tx $$ where $\bar b = B^{-1} b$ and $\xi$ is the "indicator vector" which is usually put at the top or bottom of simplex tableau. But I do not understand why each…
Wei Zhong
  • 457
1
vote
1 answer

Showing a point in a polyhedron is an extreme point

Attempt Suppose $x_1 \neq x_2$ are two points in $P$ such that $0 = \lambda x_1 + (1- \lambda) x_2$ for $\lambda \in (0,1)$. IF we make $\lambda = 1/2$ then we see that $0 = \frac{1}{2} x_1 + \frac{1}{2} x_2 \implies x_1+x_2= 0$. this implies that…
James
  • 3,997
1
vote
1 answer

Trying to prove an statement with unclear premises

Attempt First of all, I am confused as to the wording of the problem, they say the new constrain is $a^T x \geq \beta$, but they didnt say what $a$ is. Can we assume is a row of $A$? IF so, then here is what I can do: Since $x^*$ is feasible to the…
James
  • 3,997
1
vote
1 answer

simplex method: zero nonbasic variables, zero the leaving variable

I am learning the simplex method and was wondering why we always search for solutions of the form basic $\cup$ nonbasic where nonbasic variables take on zero value. Let's look at a concrete example: let 8$x_1$+10$x_2$+7$x_3$=…
1
vote
1 answer

Simplex method (need a clarification of an obvious fact)

We wish to minimize $y^Tb$ subject to $y\ge0$ and $y^TA\ge c^T$. Why is it true: if $-c\ge0$ and $b\ge0$, the (obvious) minimizer is $y=0$. I cannot seem to figure this thing out, albeit the text states that it is obvious. Perhaps I am having one…
1
vote
1 answer

linear programming problem- formulation and solution

Two tailors P and Q earn \$150 and \$200 per day respectively. P can stitch 6 shirts and 4 trousers a day, while Q can stitch 10 shirts and 4 trousers a day. How many days should each work to produce at least 60 shirts and 32 trousers at minimum…
1
vote
0 answers

Shadow Prices symmetry in Linear Programming

In linear programming problems the shadow price of a constraint is the difference between the optimised value of the objective function and the value of the objective function, evaluated at the optional basis, when the right hand side (RHS) of a…
Koinos
  • 191