Linear programming, interested in only 1 variable

Question

0 个投票

Hello

It might be a stupid question, but I'm a bit confused. You have

inequalities, want to find the smallest for example

value.

So you need to solve

s.t.

. Calling a solver will give a result with

Is this the correct way to solve it?

variable values are meaningless

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Answer 1

Bruno Luong 2019-9-16

编辑：Bruno Luong 2019-9-16

2 个投票

If you want to minimize x1 under A*x <= b

f = zeros(size(x));
f(1) = 1;
x = linprog(f, A, b);

(x2,...,xn) is not meaningless, it's the associate components such that your constraint A*x <= b is satisfied.

Imagine you want to find most left corner of a 2D triangle.

It can be written as

A*x <= b

with x is 2 x 1, A is 3 x 2, b and 3 x 1.

the LINPROG returns you (x1,x2) coordinates of the left most corner (minimize x1) even if you ignore x2 it's still the ordinate of the corner.

Richárd Tóth 2019-9-16

all clear now thanks