## Linprog error "-96@30"?

### Aron Brenner (view profile)

on 18 Sep 2019
Latest activity Commented on by Aron Brenner

on 19 Sep 2019

### John D'Errico (view profile)

When I try to use linprog in MATLAB, it returns the error:
LINPROG has stopped because it encountered an internal error. We are sorry for the inconvenience.
I tried to run the following code:
f = [3,3.4]
A = [3,4]
b = [20000]
linprog(f,A,b,[],[],[0 0],[10000 10000])
Any help would be greatly appreciated. Thanks!

### John D'Errico (view profile)

on 18 Sep 2019

You are trying to solve the problem of minimizing
3*x + 3.4*y
subject to the constraint
3*x + 4*y <= 20000
with bounds of [0,10000] for both x and y.
The solution seems pretty clear to me. It will happen at x=y=0. What does linprog say?
linprog(f,A,b,[],[],[0 0],[10000 10000])
Optimal solution found.
ans =
0
0
So it had no problems at all.
My guess is one of two things happened. You might be using an old MATLAB release, and possibly there was a bug. I seriously doubt that. As this is a trivial problem to solve.
An alternative is you have your own code named linprog. So do these things. First, tell us what release you are using. If you don't, then all I can say is sorry, but it worked perfectly fine using a current release.
Then, look closely at the result of:
which linprog -all
Does it show something strange? Have you written your own version of linprog? There should be only one copy of linprog. In my case, it lives here:
/Applications/MATLAB_R2019a.app/toolbox/optim/optim/linprog.m

Aron Brenner

### Aron Brenner (view profile)

on 18 Sep 2019
Thanks for the help! I am indeed using an older version of MATLAB. I realized I should have been minimizing -3*x - 3.4*y, so I changed f to be [-3, -3.4]. I still received the same error message, so I'm currently installing MATLAB 2019. Hopefully this will fix the problem. Thanks again!
John D'Errico

### John D'Errico (view profile)

on 18 Sep 2019
It should do so. I have no idea why it failed, as that is a pretty simple problem to solve.
Aron Brenner

### Aron Brenner (view profile)

on 19 Sep 2019
Yep that fixed the problem. Thanks!