<html><head></head><body><div style="font-family: Verdana;font-size: 12.0px;"><div>Hello Pierre-Emmanuel,</div>
<div> </div>
<div>without any limit on time, B&B nodes, or gap, Couenne will run until it closes the gap, i.e. until the lower and upper bounds match. It seems that it can't find a better solution than -0.8535 and can't raise the lower bound from -1.</div>
<div> </div>
<div>You can specify the option "time_limit" to stop it at some point. It is correct as you say that if you impose an allowable_gap option that is just above the current gap the optimization will stop, but, as you ask in your second question, it won't certify optimality. This can only happen if you let it run to completion.</div>
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<div> </div>
<div>Regards,</div>
<div>Pietro</div>
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<div style="margin:0 0 10px 0;"><b>Sent:</b> Thursday, April 09, 2020 at 3:44 PM<br/>
<b>From:</b> "Pierre-Emmanuel Emeriau" <emeriau.pe@gmail.com><br/>
<b>To:</b> couenne@list.coin-or.org<br/>
<b>Subject:</b> [Couenne] Couenne keeps running outputting the same B&B value</div>
<div name="quoted-content">Hello,<br/>
<br/>
I am having some issue trying to solve my bilinear nonconvex problem (of<br/>
small dimension, attached if needed). I am using couenne interfaced with<br/>
pyomo.<br/>
I am expected the optimal value to be around 0.85 but when I launch the<br/>
solver, couenne seems to be blocked at the same line:<br/>
```Cbc0010I After 4200 nodes, 1329 on tree, -0.85355341 best solution,<br/>
best possible -1 (15.43 seconds)````.<br/>
And it keeps going on as if it cannot terminate the branch&bound<br/>
algorithm. The solution seems good to me but I am wondering why couenne<br/>
does not stop at some point. If I set ```allowable_gap``` to an<br/>
unreasonable value (above 0.15) it will terminated and I assume this is<br/>
because:<br/>
```Cbc0011I Exiting as integer gap of 0.14644659 less than 0.15 or 0%```.<br/>
But not if I set this flag to a value below 0.14. Maybe it cannot close<br/>
the gap. Could that be the case? Which brings me to my next question:<br/>
can I certify optimality?<br/>
<br/>
Thanks a lot for your help.<br/>
Best,<br/>
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