[Ipopt] Null pointer crash

[Plett, Kelly]

Hi Andreas,

I've been meaning to get back to the list that it was completely my
fault.  Hans' original reply triggered my memory enough to look at some
code I'd added to BacktrackingLineSearch::DoBacktrackingLineSearch.  In
order to cope with an infinite loop in one particular problem, I added
the highlighted code:

      while (alpha_primal>alpha_min ||
             n_steps == 0 ) {
        // always allow the "full" step if it is
        // acceptable (even if alpha_primal<=alpha_min)
        Jnlst().Printf(J_DETAILED, J_LINE_SEARCH,
                       "Starting checks for alpha (primal) = %8.2e\n",
                       alpha_primal);

>       if (alpha_primal-alpha_min < 1.0e-10) {
>         alpha_primal = alpha_min;
>         Jnlst().Printf(J_DETAILED, J_LINE_SEARCH, "Setting alpha to
ALPHA_MIN after %d steps\n", n_steps);
>         break;
>       }

Not sure how appalling it is, but it got that particular case solving
again (I can't remember the details, but alpha_primal had slowly worked
its way to be 1e-200 above alpha_min or something like that).  Anyway,
after I added "&& n_steps > 0" to that hack, the crash disappeared.

Thanks again,
Kelly 

> -----Original Message-----
> From: Andreas Waechter [mailto:andreasw at watson.ibm.com] 
> Sent: February 2, 2010 9:28 AM
> To: Plett, Kelly
> Cc: ipopt at list.coin-or.org
> Subject: Re: [Ipopt] Null pointer crash
> 
> Hi Kelly,
> 
> Have you been able to fix this in the meantime?  I have not 
> seen this problem before, and since it is at the heart of the 
> code, it would surprise me if you found a bug there.
> 
> However, if you can still reproduce this error, I suggest you 
> first check your code with a memory checker to make sure 
> there is no issues with writing into invalid memory or using 
> unintialized values.  If you can't find anything with this, 
> please let us know what options you are using. 
> Also, have a look at the output file for a print_level at 
> least 7 and see if you see something strange before the error 
> occurs (e.g., did your code return false when evaluating any 
> of the problem functions or derivatives)...
> 
> Regards,
> 
> Andreas
> 
> On Mon, 18 Jan 2010, Plett, Kelly wrote:
> 
> > Hi all,
> >
> > We have been using Ipopt with good success to optimize various 
> > black-box process models, so thanks to all who have 
> contributed to the project.
> > However...
> >
> > Recently I have been running into an increasing number of crashes in
> > IpoptCalculatedQuantities::curr_d_minus_s() on a null s 
> pointer.  When 
> > I bump up COIN_IPOPT_CHECKLEVEL to 3, I observe SmartPtr assertions 
> > starting in IpoptCalculatedQuantities::trial_slack_x_L() because
> > ip_data_->trial()->x() is null.  This occurs in AcceptTrialPoint on 
> > the max_correction = correct_bound_multiplier(...) line with the 
> > following call stack:
> > 	ipopt.dll!_wassert(const wchar_t * expr=0x0f594ea4, 
> const wchar_t * 
> > filename=0x0f594e40, unsigned int lineno=433)  Line 384 C
> > 	ipopt.dll!Ipopt::SmartPtr<Ipopt::Vector const >::operator*()
> > Line 433 + 0x1c bytes	C++
> > 	ipopt.dll!Ipopt::IpoptCalculatedQuantities::trial_slack_x_L()
> > Line 357 + 0x8 bytes	C++
> > 	ipopt.dll!Ipopt::IpoptCalculatedQuantities::trial_compl_x_L()
> > Line 1823 + 0xc bytes	C++
> >> 	ipopt.dll!Ipopt::IpoptAlgorithm::AcceptTrialPoint()  Line 658 +
> > 0x1d bytes	C++
> > 	ipopt.dll!Ipopt::IpoptAlgorithm::Optimize(bool isResto=false)
> > Line 367	C++
> >
> > Being new to the internals of Ipopt, under what conditions will the 
> > trial x vector be null?  Is there anything specific I 
> should look for 
> > in the diagnostics that might help me identify the root cause?  Any 
> > guidance would be greatly appreciated!
> >
> > The case in which I am currently observing this behaviour 
> is tiny (one 
> > variable, one inequality), but I have seen it in larger 
> ones as well.  
> > I can reproduce in both Ipopt 3.6.0 and 3.8.1.
> >
> > Thanks in advance,
> > Kelly
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