[Coin-discuss] CBC applied to maximization problems

[Laszlo Ladanyi]

Francois has submitted code to print a warning message:

   if(objsense == -1) {
     printf("### WARNING: CoinLpIO::readLp(): Maximization problem
reformulated as minimization\n");
     objectiveOffset_ = -objectiveOffset_;
   }

It has been committed to stable/2.3 and to trunk.

--Laci

On Tue, 2 Dec 2008, Hart, William E wrote:

>
> Mike:
>
> But how does the wrapper know when to flip, if it's simply being handed an LP file?  Do I need to parse the LP file before CBC does?
>
> I can't think of a way of dealing with this that isn't kludgey.
>
> --Bill
>
>> -----Original Message-----
>> From: Michael Hennebry [mailto:hennebry at web.cs.ndsu.nodak.edu]
>> Sent: Tuesday, December 02, 2008 8:27 PM
>> To: Hart, William E
>> Cc: fmargot at andrew.cmu.edu; coin-discuss at list.coin-or.org
>> Subject: Re: [Coin-discuss] CBC applied to maximization problems
>>
>> On Tue, 2 Dec 2008, Hart, William E wrote:
>>
>>> Here's my scenario.  I have a wrapper script that passes a
>> LP or MPS file to CBC, and then parses the output.  The
>> results of this optimization process are then returned to the
>> user.  The confusing thing is that a user sees minimization
>> results when passed a maximization problem.  Logically, it's
>> identical, but this will be surprising and confusing to
>> non-technical users.
>>
>> I think that the answer is to have the wrapper do the flipping.
>> The wrapper can print the warning.
>> The wrapper could also negate any output that needed negating.
>>
>>> If CBC/CoinLpIO simply printed a warning that this problem
>> was being reformulated, that would be enough for me to
>> correctly parse the output.  (Working with the library
>> directly, this wouldn't be an issue because I could check the
>> max/min sense of the original problem...).
>>
>> --
>> Michael   hennebry at web.cs.ndsu.NoDak.edu
>> "Pessimist: The glass is half empty.
>> Optimist:   The glass is half full.
>> Engineer:   The glass is twice as big as it needs to be."
>>
>>
>
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