Re: [Help-glpk] [Fwd: Interface for exact solutions]

[Heinrich Schuchardt]

Hello Nico,

so your current changeset is in branch get_exact_values.
https://github.com/nicodelpiano/glpk/commits/get_exact_values

Thank you for your contribution.

I have started reviewing the changes. Some parts of the code may have to
be adjusted before Andrew can integrate them:

Do we need three different scmp structures and three initalization
routines? I suggest to add the additional parameters to the existing
smcp structure.

smcp->exact_size is only used in malloc statements. That is strange.
Shouldn't the following code consider the value you have chosen for
exact_size?

You dereference parm for malloc. Afterwards you check if it is NULL.
You should move the check to before malloc.

Why do you malloc at all? You are calling mpz_get_str with str = NULL.
So you request allocation of memory here.

smcp is a parameter structure. You should not put results there.
Why can't you use the glp_prob structure for transfering the results?

Do we really need glp_exact_sol()? Can't the result transfer be
integrated in the existing glp_exact() function?

mpz_get_str should be called with a custom allocator using xmalloc and
xfree. Use mp_set_memory_functions to set custome allocation function.
This will make it easier to identify mermory leaks.

When I checked out the branch it contained a superfluous file "prec".

Best regards

Heinrich Schuchardt


On 07/12/2016 03:39 PM, Nico Del Piano wrote:
> Hello Heinrich,
> 
> thanks for your fast reply and sorry for the code, yes, it was a complete 
> mess!
> 
> I created a new cleaned branch, this is the specific commit
> https://github.com/nicodelpiano/glpk/commit/da11fac3996d9ed1012f1c50e76971e20f2b343e
> 
> I am using gmp, so I first configure the project with --with-gmp.
> 
> Best regards,
> 
> Nico.
> 
> 2016-07-12 9:48 GMT-03:00 Heinrich Schuchardt <address@hidden>:
>> Hello Nico,
>>
>> your mail had to be forwarded manually because you're not subscribed to the 
>> GLPK Help list.
>>
>> In GitHub the history of the exactsolver branch is messed up.
>>
>> You have been committing all sorts of files which are not source like 
>> configure.log, •.o, ...
>>
>> I cannot find any meaningful commit messages.
>>
>> Please, create a clean branch.
>>
>> Best regards
>>
>> Heinrich Schuchardt
>>
>> http://www.xypron.de
>>
>> Am 12.07.16 um 14:35 schrieb Andrew Makhorin
>>
>>> -------- Forwarded Message --------
>>> From: Nico Del Piano <address@hidden>
>>> To: address@hidden
>>> Subject: Interface for exact solutions
>>> Date: Tue, 12 Jul 2016 08:44:39 -0300
>>>
>>> Hi all,
>>>
>>> I'm using the exact simplex solver provided by glpk to compute exact
>>> solutions from a project written in Java (using the Java bindings
>>> java-libglpk) and I haven't found a way to retrieve those exact
>>> values: I'm getting double precision solutions.
>>>
>>> To overcome this, I defined a not-so-pretty interface to store these
>>> exact values (I provided two ways to do this, both for rational
>>> precision and fixed precision) here [1]. Basically, I just copied the
>>> `glp_smcp` structure and added some parameters to properly store the
>>> solutions in the desired precision. I also added two solvers
>>> `glp_exact_sol` (for rationals) and `glp_fixed_sol` (for user-defined
>>> precision). For example, if we use the `glp_fixed_sol` solver, we can
>>> specify in the structure the precision we want, and store there the
>>> solutions, in order to get those values later on.
>>>
>>> Obviously, this doesn't seem to be the best approach, so the purpose
>>> of this email is to discuss how to improve this interface, or, even
>>> better, how to add this feature in glpk. Furthermore, if you think
>>> this can be done in glpk and I'm just ignoring it, please let me know.
>>>
>>> Thanks,
>>>
>>> Nico.
>>>
>>> [1]: https://github.com/nicodelpiano/glpk/tree/fixed_precision
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> Help-glpk mailing list
>>> address@hidden
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>