[Dip] good news

[Matthew Galati]

Hi Ayse,

Replying to the DIP mailing list since this might be relevant to other users - although I think you are the only one so far. :)


I am assuming the following happens when solving the subproblem - i.e., one of your blocks.
"Coin0508I Presolve thinks problem is unbounded
Error: CBC IP solver 2nd status = 7"

This is because the BCP method in DIP does not consider extreme rays. Rather it assumes that the feasible region is bounded in all directions. I have yet to see any real-world example where extreme rays are needed. It should be easy to bound your feasible region by giving lower and/or upper bounds to all your variables - even if they are artificially big. Try that and see if that helps. In some future release of DIP, I will add extreme rays so this can be dealt with more naturally.



"I am kind of confused why one method does not work and the others do and also I am wondering how to decide which method to use, is there any documentation that I can read about this?"

There is no real documentation to help a user decide this. In fact, that is part of why we wrote DIP - so it is easy to try different methods without having to recode anything.

See
  https://coral.ie.lehigh.edu/~magh/decomp/decomp_INFORMS09.pdf  and
  http://coral.ie.lehigh.edu/~ted/files/papers/DECOMP04.pdf
for some background information on the different algorithms. There will be much more detail in my thesis - which is due out in one month. I will post that when it is complete.

Thanks,
Matt



From: Ayse Durukan [mailto:adurukan at mail.uh.edu]
Sent: Thursday, October 29, 2009 2:08 PM
To: Matthew Galati
Subject: Re: RE: good news

Hi Mr. Galati,
I tried converting the mps files using cplex and it worked. Also manually removing the lines before NAME header helps too.
After converting the files, I kept getting the same error until I start playing with the main settings. When I solve it with DIP's CPM method it works fine.
When I solve it with DIP's BCP method it gives following error
Coin0508I Presolve thinks problem is unbounded
Error: CBC IP solver 2nd status = 7
When I set doCut=1 and doDirect=1 it works too.
I am kind of confused why one method does not work and the others do and also I am wondering how to decide which method to use, is there any documentation that I can read about this?
Also, please see the attachment for the problem's mps files and block files.

Thank You
Ayse