Linear Programming solvable by MATLAB

Question

I want to solve linear Programming by MATLAB . For this purpose , I am following the following link . Linear Programming .

Here , a sample problem is given :

Find x that minimizes

f(x) = –5x1 – 4x2 –6x3,

subject to

x1 – x2 + x3 ≤ 20 3x1 + 2x2 + 4x3 ≤ 42 3x1 + 2x2 ≤ 30 0 ≤ x1, 0 ≤ x2, 0 ≤ x3.

First, enter the coefficients

f = [-5; -4; -6]; A = [1 -1 1 3 2 4 3 2 0]; b = [20; 42; 30]; lb = zeros(3,1);

Next, call a linear programming routine.

[x,fval,exitflag,output,lambda] = linprog(f,A,b,[],[],lb);

My question is that what is meant by this line ?
lb = zeros(3,1); Without this line , all problems solvable by MATLAB is seen as infeasible . Can you help me in this purpose ?

Bentoy13 · Accepted Answer · 2014-04-16 11:30:52Z

1

This is not common to ALL linear problems. Here you deal with a problem where there are some constraints on the minimal values of the solution:

0 ≤ x1, 0 ≤ x2, 0 ≤ x3

You have to set up these constraints in the parameters of your problem. The way to do so is by specifying lower boundaries of the solution, which is the 5th argument.

Without this line, the domain on which you search for a solution is not bounded, and exitflag has the value -3 after calling the function, which is precisely the error code for unbounded problems.

answered Apr 16, 2014 at 11:30

Bentoy13

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3 Comments

osimer pothe Over a year ago

I have another basic fundamental problem in solving linear programming problem by matlab . Can you please help me ?

Bentoy13 Over a year ago

Post a new question on SO :)

osimer pothe Over a year ago

stackoverflow.com/questions/23109138/…

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