[Coin-discuss] re: Preserving row and column names using readLP & OsiSolverInterface

[Francois Margot]

Matt:

I sent the new version to Laci on Wednesday 2/8.

Francois

On Fri, 10 Feb 2006, Matthew Saltzman wrote:

> Are there unit test changes in the offing related to this issue? Currently, 
> the OSI unit test fails (at least with CPLEX) when saving and reading back a 
> problem with non-unique row names.
>
> On Mon, 6 Feb 2006, Matthew Saltzman wrote:
>
>> On Mon, 6 Feb 2006, Francois Margot wrote:
>> 
>>> 
>>> John:
>>> 
>>> I will make the changes. Note that, as far as I know, it is impossible
>>> to specify ranged constraints in the "Cplex" LP format
>>> (see http://plato.asu.edu/cplex_lp.pdf). They have to be written
>>> as two separate constraints.
>> 
>> Or as equality with explicit bounded slack.
>> 
>> I tried setting a bound on a constraint in CPLEX, but it appeared not to do 
>> the right thing.
>> 
>> 		Matt
>> 
>> 
>>> 
>>> Francois
>>> 
>>> 
>>> On Mon, 6 Feb 2006, John J Forrest wrote:
>>> 
>>>> Francois,
>>>> 
>>>> OK - tighten restrictions on row names but then writeLP should be 
>>>> changed.
>>>> writeLP must produce a valid model from a valid model.  Either it must be
>>>> enforced that changeNameOnrange be true or a better alternative is to
>>>> write out the ranged constraint correctly.
>>>> 
>>>> John Forrest
>>>> 
>>>> 
>>>> 
>>>> Francois Margot <fmargot at andrew.cmu.edu>
>>>> Sent by: coin-discuss-bounces at list.coin-or.org
>>>> 02/04/2006 08:54 AM
>>>> Please respond to
>>>> Discussions about open source software for Operations Research
>>>> <coin-discuss at list.coin-or.org>
>>>> 
>>>> 
>>>> To
>>>> Discussions about open source software for Operations Research
>>>> <coin-discuss at list.coin-or.org>
>>>> cc
>>>> 
>>>> Subject
>>>> Re: [Coin-discuss] re: Preserving row and column names using readLP     &
>>>> OsiSolverInterface
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>>> On Thu, 2 Feb 2006, John J Forrest wrote:
>>>> 
>>>>> Francois,
>>>>> 
>>>>> I strongly disagree.  If there are no names or no duplicates then the
>>>> code
>>>>> I added is not invoked.  If there are duplicates then without my change
>>>>> accessing some row names will give a segmentation error.  The hash
>>>>> functions are never used for row names and it is only row names I am
>>>>> checking.
>>>> 
>>>> First, there is now a memory leak: since stopHash(0) sets numberHash[0] 
>>>> to
>>>> 0,
>>>> when the CoinLpIO object is deleted, the array names_[0] is not freed
>>>> properly.
>>>> 
>>>> Second, the method CoinLpIO::rowIndex() now sometimes behaves 
>>>> incorrectly:
>>>> 
>>>> asking for the index of a row having a particular name always returns -1,
>>>> i.e. it claims that no name is in the list of row names.
>>>> 
>>>>> 
>>>>> So I think my solution does not harm anyone and helps people who have
>>>>> duplicates.
>>>> 
>>>> One bug is replaced by two. I am not convinced that this is an 
>>>> improvment.
>>>> 
>>>> I think that we have to decide if we want to support duplicate row names
>>>> or not. In the current implementation, the warning that is printed when
>>>> non distinct row names are identified was intended to warn the user that
>>>> strange behavior (including possible seg faults) might come from that
>>>> fact.
>>>> 
>>>> If we want to fully support identical row names, I see 2 possibilities:
>>>> 
>>>> 1) Remove hash tables for row names and replace them by a vector. This
>>>> requires
>>>> changes in several methods dealing with row names.
>>>> 
>>>> 2) Have hash tables storing duplicates. Requires a new set of hash table
>>>> methods.
>>>> 
>>>> In addition, we have to provide a method that returns all the indices of
>>>> rows
>>>> having a given name.
>>>> 
>>>> The other possibility (my preference) is to tighten the restrictions on
>>>> names:
>>>> all row names must be distinct. If non distinct names are provided, then
>>>> either an error is raised or the names are automatically replaced by
>>>> default
>>>> names.
>>>> 
>>>> I can make the changes once we agree on what we want to do.
>>>> 
>>>> Francois
>>>> 
>>>> 
>>>> 
>>>> _______________________________________________
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>>>> Coin-discuss at list.coin-or.org
>>>> http://list.coin-or.org/mailman/listinfo/coin-discuss
>>>> 
>>>> 
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>> 
>> 
>
> -- 
> 		Matthew Saltzman
>
> Clemson University Math Sciences
> mjs AT clemson DOT edu
> http://www.math.clemson.edu/~mjs
>
>