[Cbc] integer overflow in CglGomory.cpp

[Haroldo Santos]

Hi,

AFAIK, now there are two Gomory cut generators available in CBC (Cgl):
 CglGomory and CglGMI.  Does this overflow affects both versions ?
Which version is recommended for general use now ?  Should we do some tests
to determine that ?



2017-05-16 15:44 GMT-03:00 John Forrest <john.forrest at fastercoin.com>:

> Modified in trunk (can be copied to stable).  Just for now I have left it
> as was unless GOMORY_LONG is defined in configure.  If anyone is interested
> they could see what difference it makes (on my first test it was slower -
> but then invalid cuts can be very powerful!).  There may be some connection
> with queries about accuracy of Gomory cuts in 2015 (GOMORY_RELAX_NUMBER).
>
> John Forrest
>
>
> On 16/05/17 10:47, Tobias Stengel wrote:
>
> Hi,
>
>
>
> I noticed an integer overflow in CglGomory.cpp / nearestRational(double,
> int) lines 445 and 446. That specific MIP is solved correctly, but I have
> no idea whether such an overflow can lead to wrong cuts that e.g. cut off
> the optimal solution. Anyway integer overflow is undefined behaviour in
> C/C++ and the returned fractional is not „near“ the input…
>
>
>
> 2 parameter sets for nearestRational that lead to overflow can be found in
> the attached test program. Does anyone know how nearestRational works and
> how the overflow can be fixed properly?
>
>
>
> Thanks
>
>
>
> Tobias
>
>
>
>
>
>
>
>
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-- 
=============================================================
Haroldo Gambini Santos
Computing Department
Universidade Federal de Ouro Preto - UFOP
email: haroldo [at ] iceb.ufop.br
home/research page: www.decom.ufop.br/haroldo


It has long been an axiom of mine that the little things are infinitely
the most important.
-- Sir Arthur Conan Doyle, "A Case of Identity"
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