linprog gives wrong solution?

Hi

I am trying to solve a simple linear programming problem in matlab:

500x + 400y -> min

x + y >= 90

0.02x + 0.05y <= 2.7

3x + 5y <= 360

According to the manual this should solve the problem:

f = [500, 400];

A = [-1 -1; 0.02 0.05 3 5];

b = [-90 0.03*90 4*90]';

[x, fval, info] = linprog(f, A, b)

I received the answer:

x=[60 30];

fval = 4.20e4;

info=1

On the other hand, the vertices of the area of acceptable solutions and the value of the function are as follows:

xy=[60 30; 90 18; 45 45]

f = 1e4*[4.2000 5.2200 4.0500]

It looks like the actual minimum is 4.05e4. What am I doing wrong? How to interpret this result?

Answer 1

[John D'Errico]

I'm surprised that you think [45 45] is a possible solution.

.02*45 + .05*45
ans =
       3.15

That is less than 2.7? Must be the new math.

Maybe you should consider if you have determined the shape of that region properly?

[Stan]

Fortunately, this is not a new math just my mistake in the calculation. Thanks