[Clp] Incorrect solution for LP problem

[Ted Ralphs]

I am the guilty party who made the changes to CoinLpIO. I was extending the
reader so that it recognizes multiple objectives. I am also not an expert
on the LP format, but what is wrong here is that the objective does not
have a name. If you change it to:

Minimize
  obj: C1

then it should work as expected. If there is only one objective, It is
supposed to assign the default name of "obj" and looking at the code, it
seems it should still be doing that. However, it is throwing an error. I
will debug it and let you know.

Cheers,

Ted

On Wed, Oct 22, 2014 at 2:46 PM, John Forrest <john.forrest at fastercoin.com>
wrote:

> Kish,
>
> Seems to be a change to CoinLpIO - objective is being ignored - something
> to do with no objective name possibly.  Coding has changed for CoinlpIO but
> I am not an expert.  Will look at it tomorrow morning, unless whoever made
> changes to CoinLpIO fixes problem before then.
>
> John
>
>
> On 22/10/14 18:28, Kish Shen wrote:
>
>> Hi,
>>
>> I updated CBC yesterday (for dealing with handling of messages via
>> message handlers -- thanks John!), but this CBC is failing one of our
>> existing tests. It looks like the problem is in CLP, as CLP seems to be
>> returning an incorrect objective value for the following LP problem:
>>
>> \Problem name: eclipse3
>>
>> Minimize
>>   C1
>>
>> Subject To
>> R1: C1 + C2 >= 7
>> R2: - C2 + C1 = 0
>>
>> Bounds
>> C1 free
>> C2 free
>>
>> End
>>
>> The objective should be 3.5, but 0.0 is returned.
>>
>> I have been able to reproduce this problem using the clp executable --
>> by import(ing) the LP file and then solve.
>>
>> This is from CBC 2.8 that I downloaded yesterday. The problem was not in
>> the earlier CBC 2.8 that I was using, which was probably downloaded about a
>> year ago.
>>
>> Is this a problem in CLP, or am I doing something wrong?
>>
>> Thanks in advance for any help/information!
>>
>> Cheers,
>>
>> Kish
>> _______________________________________________
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>> Clp at list.coin-or.org
>> http://list.coin-or.org/mailman/listinfo/clp
>>
>>
>>
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-- 
Dr. Ted Ralphs
Professor, Lehigh University
(610) 628-1280
ted 'at' lehigh 'dot' edu
coral.ie.lehigh.edu/~ted
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