[Ipopt] Null pointer crash

[Plett, Kelly]

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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