Authors

  • S.M.Kamoldinov

Author Biography

  • S.M.Kamoldinov

    Tashkent State University of Economics

    kamoldinovs03@gmail.com

DOI:

https://doi.org/10.71337/inlibrary.uz.mead.116622

Keywords:

Multi-argument linear function argument linear constraints extremum graphical method mathematical modeling objective function.

Abstract

This article deals with bringing economic problems to the problem of linear programming and solving them graphically. Also, at first, linear programming will be touched upon, its solution methods and mathematical interpretation of the given problem: a special emphasis will be placed on solving it through a linear function. As an example, the issue of optimal production planning for the “Olmos” furniture factory is given.


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ECONOMIC PROBLEMS INTO LINEAR PROGRAMMING PROBLEMS

AND SOLVING THE SIMPLEX METHOD

S.M.Kamoldinov

Tashkent State University of Economics

kamoldinovs03@gmail.com

Login

As is known, problems related to the theory and application of

quantitative methods and models are solved by bringing them to the problem of linear

programming. The condition of certainty is understood as a situation in which all

parameters and conditions of system control are certain, that is, there is no random

effect. In such problems, the method of linear optimization is used, which aims to

create an optimal production plan, determine the optimal volume of trade, purchase

or transportation, optimal financial planning, and similar goals. Planning is one of the

main functions of management.

Annotation. This article deals with bringing economic problems to the

problem of linear programming and solving them graphically. Also, at first, linear

programming will be touched upon, its solution methods and mathematical

interpretation of the given problem: a special emphasis will be placed on solving it

through a linear function. As an example, the issue of optimal production planning

for the “Olmos” furniture factory is given.

Key words: Multi-argument linear function, argument, linear constraints,

extremum, graphical method, mathematical modeling, objective function.

If the number of variables in the mathematical model of a linear

programming problem is more than two (with some exceptions), the problem cannot

be solved graphically. The simplex method is used to solve such problems.

The simplex method is a method of successively moving from one basic

solution (one end of the solution polygon) to another until the objective function of a

linear programming problem takes the optimal (maximum or minimum) value. This


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method is a universal method that allows you to solve any linear programming

problem, unlike the graphical method, which is designed to solve problems with only

two variables. is considered .

The simplex method was proposed in 1947 by the American

mathematician R. Danzig, and since then it has been widely used in industrial

production to solve linear programming problems involving thousands of variables

and constraints. Before describing the simplex method, let us recall some concepts of

a system of linear equations.

To us

n

variable

m

Given a system of equations:

11 1

12 2

1

1

21 1

22 2

2

2

1 1

2 2

...

...

......................

...

n n

n n

m

m

mn n

m

a x

a x

a x

b

a x

a x

a x

b

a x

a

x

a x

b

 

 

 

(1)

In linear programming problems

(

)

ij

A

a

(

1, 2, ...,

;

1, 2, ..., )

i

m j

n

matrix color

r

m

is,

m

n

The situation is interesting.

If (1) the system

m

If the determinant of the matrix formed from the

coefficients before the variables is different from zero, then the basis for such

variables is are called variables .

remaining

n m

variables are either independent or non-independent. are

called variables .

If (1) the system

1

2

( ,

, ...,

)

n

x x

x

solutions

0

j

x

(

1, 2, ..., )

j

n

If the

condition is satisfied, such solutions are called feasible solutions, otherwise they are

called impossible solutions .

A solution to a system in which the non-basic variables are zero is called

a basic solution .

Analysis and results

For convenience in calculations, it is advisable to present the simplex

method in tabular form.

Simplex table.

The following algorithm is used to solve linear

programming problems using the simplex method.


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Step 1. Construct an initial simplex tableau;

Step 2. Check the solution for optimality. End the process when an

optimal solution is found;

Step 3. Find the state that leads to optimality;

Step 4. Switch to a new solution and return to step 2.

The general form of a simplex table is given in Table 1 (

m

– number of

conditions,

n

– number of variables)

Objective function

B

as

is

changers

C

oef

fi

ci

en

ts

of

the

obj

ect

ive

funct

ion

incl

uded

in

the

basi

s

B

as

is

sol

ut

ion

val

ues

Coefficients of the terms of the problem

j

F

j

j

C

F

line definition

j

j

C

F

A string defining the optimality criterion

Table 1. Simplex table view

• The first row of the table records all (main and additional) variables;

• Table

B

The first column, separated by the letter , lists the basic

variables.

• The second row of the table, starting from cell 3, lists the coefficients

of the objective function.

b

C

The coefficients of the variables included in the basis are placed in

the column (except for the last two rows).

• The coefficients of the conditions are given in the rows dedicated to the

basic variables.

0

P

The column contains the values of the basic variables.


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• Last

j

j

C

F

The line is aimed at determining the optimality criterion.

j

F

using the latest information

j

j

C

F

is a row, the last cell of which

contains the current value of the objective function.

This

1

2

1

2

1

2

1

2

2

10

2

14

0,

0

2

3

max

x

x

x

x

x

x

F

x

x

We determine the solution of the problem using the simplex method. To bring

the problem into canonical form, we use the following addition

1

s

,

2

s

We introduce

variables:

1

2

1

1

2

2

1

2

1

2

1

2

1

2

2

10

2

14

0,

0,

0,

0

2

3

0

0

max

x

x

s

x

x

s

x

x

s

s

F

x

x

s

s

 

    

(2)

There are a total of 4 equations in the system of equations, i.e. 2 basic

ones

1

x

,

2

x

and 2 additional ones

1

s

,

2

s

There are variables. The vector of coefficients

of the objective function is

C

, and the matrix of coefficients of the constraint

conditions is

A

and the right-hand side vectors of the conditions

B

are defined as

follows:

1

2

3

4

( ;

;

;

)

(2; 3; 0; 0)

C

c c c c

11

12

13

21

22

23

1

2 1

,

2

1 1

a

a

a

A

a

a

a

 

 

1

2

10

14

b

B

b

   

   

 

 

Step 1. Construct an initial simplex tableau

Let's construct a simplex table for our example above. The objective

function

1

2

1

2

2

3

0

0

z

x

x

s

s

   

Write it in the form of a table, taking into account the system (2)

We fill in the following ( Table 2 ).


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B

b

C

0

P

1

x

2

x

1

s

2

s

2

3

0

0

1

s

0

10

1

2

1

0

1

s

0

14

2

1

0

1

j

F

0

0

0

0

0

j

j

C

F

2

3

0

0

Table 2. Elementary simplex table

2, 3, and 4 of the initial simplex tableau consist directly of the objective

function and the system coefficients (

A

matrix,

C

and

B

pay attention to vectors).

j

F

The row elements are found as follows. The vector consisting of the coefficients of

the objective function in the basis is scalar multiplied by the vectors in the condition

column. That is,

0

0

b

C

 

  

 

a vector

1

1

2

A

 

  

 

is scalar multiplied by a vector, etc. In

this way

j

F

all elements of the row are found.

j

j

C

F

The row elements are the

coefficients of the objective function, respectively

j

F

is obtained by subtracting the

elements of the row. Since the variables not included in the basis are equal to zero

1

0

x

,

2

0.

x

the value of the basis variables is taken from the last column:

1

10,

s

2

14.

s

j

F

The number in the last cell of the row is the value of the objective function

at the initial step.

0.

F

In the first step, the values of the last row match the coefficients of the

objective function. This completes the first step.

Step Two. Check the result for optimality

Optimality of the obtained result

j

j

C

F

is determined by the non-negativity

of all numbers in the row. If

j

j

C

F

all elements in the row are zero or negative If the

result obtained is optimal and the process is completed. If there is at least one positive

element among these elements, then optimality has not been achieved and the solution

can be improved.


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In our example, the result is not optimal because the last row contains

two positive numbers. This completes the verification of the optimality condition.

Step Three. Finding the optimality-directing state

We determine the maximum element from the last row of the initial table,

which is equal to 3. The column containing the largest positive element in the last row

of the simplex table is called the decisive column (Table 3).

B

b

C

0

P

1

x

2

x

1

s

2

s

0

/

ij

P

a

2

3

0

0

1

s

0

10

1

2

1

0

10/2=5

1

s

0

14

2

1

0

1

14/1=14

j

F

0

0

0

0

0

j

j

C

F

2

3

0

0

Table 3. Determination of the decisive element

In the table given in Table 3, the decisive column is indicated by an arrow. In

order to find the decisive row, we introduce an additional column and divide the

elements of the column by the elements of the decisive column. We take the smaller

of the resulting numbers:

min{5, 14} 5.

Therefore, the third row of the table is the

decisive row, and this row is indicated by an arrow. The element located at the

intersection of the decisive row and the decisive columns is the decisive is called the

element . In our example, the decisive element is equal to 2 and is shown in red in the

table. This completes step 3.

Step 4. Switch to a new solution

The transition to a new solution begins with the exchange of basic variables.

The basic variable at the beginning of the solution row is exchanged with the variable

in the solution column, and the corresponding coefficients are also exchanged. The

elements in rows 3 and 4 of the simplex table are recalculated using the Gauss-Jordan

method using the solution element. The Gauss-Jordan method proceeds as follows:

1) The decisive row is divided by the decisive element. The remaining

elements of the decisive column are filled with zeros.


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2) The remaining rows are recalculated using the "rectangle" method. You are

familiar with this method from the topic of solving a system of linear equations using

the Gauss-Jordan method.

Let's mention the "rectangle" method.

( , )

ij

a i j

a

Let us define the element at

the intersection of

( , )

a s k

the -row and -column

j

of a table such as . Let

i

– be the

decisive element and

( , )

a i j

the element to be recalculated. The table

( , )

a s k

and

( , )

a i j

Using the cells containing the values, we can construct a right rectangle as

shown in Table 4 below.

( , )

a i j

( , )

a i k

( , )

a s j

( , )

a s k

Table 4. Rectangle method

( , )

a i j

new value of

*

( , )

a i j

is calculated using the following formula:

*

( , )

( , )

( , )

( , )

( , )

a s j

a i k

a i j

a i j

a s k

As a result of the recalculation, we arrive at the following table 5. Thus, a

second table was constructed, and a new simplex table was created.

To speed up calculations, it is advisable to use the following rules.

B

b

C

0

P

1

x

2

x

1

s

2

s

2

3

0

0

2

x

3

5

1/2

1

1/2

0

1

s

0

9

3/2

0

–1/2

1

j

F

15

3/2

3

3/2

0

j

j

C

F

1/2

0

–3/2

0

Table 5. Second simplex table


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• If the decisive row contains elements equal to 0, the value of the

corresponding column elements remains unchanged in the new table;

• If the decisive column contains elements equal to 0, the corresponding

row in the new table remains unchanged. We proceed to the second step and check

the optimality criterion again.

The last row of the new simplex table contains a positive element

1

2

Since

there is no optimal solution, we will construct a new table. Now the decisive column

1

x

is the one corresponding to the only positive element in the last row (Table 6).

B

b

C

0

P

1

x

2

x

1

s

2

s

0

/

ij

P

a

2

3

0

0

2

x

3

5

1/2

1

1/2

0

10

1

s

0

9

3/2

0

–1/2

1

6

j

F

15

3/2

3

3/2

0

j

j

C

F

1/2

0

–3/2

0

Table 6. Determination of the decisive element

Minimum value in the last column

min{10, 6}

6

Since the decisive line is the

fourth line. So,

1

x

The variable enters the basis,

2

s

and comes out of the basis. We

construct a new table according to the above rule (Table 7).

B

b

C

0

P

1

x

2

x

1

s

2

s

2

3

0

0

2

x

3

2

0

1

2/3

–1/3

1

x

2

6

1

0

–1/3

2/3

j

F

18

2

3

4/3

1/3

j

j

C

F

0

0

–4/3

–1/3

Table 7. The last simplex table


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If we look at the last row of the resulting table, all the elements in the row are

non-negative, which indicates that we have reached the optimal solution. Optimal

plan from the table

1

6,

x

2

2

x

,

1

0

s

and

2

0

s

and the optimal value of the

objective function

max

(6; 2)

2 6

3 2 18

F

F

    

In the last table, the optimal value

of the objective function is formed in the pink cell.

Conclusion

Solving a linear programming problem using the simplex method is a

universal method, in which there is no limit to the number of variables, as in the

graphical method. In addition, the algorithm for solving a linear programming

problem using the simplex method is available in many application programs. In

particular, linear programming problems can be solved using the simplex method

using MS Excel and POM QM for Windows .

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