[Bonmin] Assertion in OsiSimpleInteger::createBranch()

[David Wilkinson]

Hi Stefan:

I will certainly upgrade to Bonmin 1.8.6, as I see it has all the 
changes regarding FORTRAN_INTEGER_TYPE and NO_CATCH_ALL that you and I 
have been discussing. Thanks for that! But are there other changes 
relative to Bonmin 1,8.4?

What do you mean by "fixed integer variable"? Do you mean one where the 
user has set the upper and lower bounds to be the same? That I certainly 
have not done.

Until recently we were using (the very ancient) Bonmin 1.3.2, and 
interestingly this problem did not arise there.

David Wilkinson

============================

On 20.06.2017 09:29, Stefan Vigerske wrote:
> Hi,
> 
> it sounds as if Bonmin tries to branch on a fixed integer variable.
> You might want to trace who created this OsiBranchingInformation and
> why this has happened.
> 
> Also consider upgrading to Bonmin 1.8.5 or 1.8.6 first. Bonmin 1.8.4
> is 21 months old.
> 
> Stefan
> 
> On 06/20/2017 03:16 PM, David Wilkinson wrote:
>> This is a Bonmin question, but I haven't seen any activity in the 
>> Bonmin group for a while, so I am sending to the Ipopt group also.
>> 
>> I am using Bonmin 1.8.4 with "B-BB" algorithm to solve a problem with 
>> two integer variables, both with lower bound 0 and upper bound 3, with 
>> an initial guess of (1,1). I am seeing an assertion error in 
>> OsiSimpleInteger::createBranch() around line 626 of 
>> OsiBranchingObject.cpp. The purpose of the assertion is to check that 
>> the upper bound for the variable under consideration is greater than 
>> the lower bound. When I hit the assertion, the value of columnNumber_ 
>> is 0, and both info->lower_[0] and info->upper_[0] are 0.0, so the 
>> assertion is correctly triggered.
>> 
>> Since assertions are not supposed to happen, I initially suspected 
>> user (me) error in setting up the problem, but I do not think so, 
>> because our driver program repeatedly requests optimizations of a 
>> similar type (with different objective and constraint functions, but 
>> the same bounds), and several such optimizations have been done 
>> correctly before this one. It may be that these optimizations do not 
>> fully satisfy the Bonmin convexity requirements, but surely this 
>> should not cause an assertion in the code? Our program will tolerate 
>> cases where Bonmin fails and emits an exception, and indeed if I throw 
>> an exception in OsiSimpleInteger::createBranch() instead of the 
>> assertion, our program continues with other successful Bonmin 
>> optimizations.
>> 
>> Any ideas?
>> 
>> Thanks,
>> 
>> David Wilkinson
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