[Couenne] Couenne error with final solution

[Akshay Gupte]

Hi Pietro,

I am running Couenne within AMPL since I have to solve some other models 
first and hence not using a .nl file as input to Couenne. I do not think 
it is writing a .sol solution file in this case. Is there another way to 
check ?

This error was reproduced on a number of instances I tried. Is this a 
bug or is there some disconnect (w.r.t. tolerances etc.) between Cbc and 
Couenne that I am not aware of ?

Regards,
Akshay

--
Akshay Gupte
Ph.D. student, Operations Research
School of Industrial&  Systems Engineering
Georgia Institute of Technology
Email: akshayg at gatech.edu


On 4/4/2012 5:43 PM, Pietro Belotti wrote:
> Akshay,
>
> Couenne sometimes finds feasible solutions that Cbc deems infeasible, 
> and hence keeps printing 1e50 as the best upper bound (the lines that 
> begin with "After 100 nodes," are printed by Cbc). You may want to 
> check if the reported upper bound of -3.562291e+04 corresponds to a 
> feasible solution, i.e., is there a .sol file?
>
> Cheers,
> Pietro
>
> -- 
> Pietro Belotti
> Dept. of Mathematical Sciences
> Clemson University
> email: pbelott at clemson.edu
> phone: 864-656-6765
> web:   http://myweb.clemson.edu/~pbelott
>
> On Wed, 4 Apr 2012, Akshay Gupte wrote:
>
>> Hi,
>>
>> I am attaching a sample output below:
>>
>>
>> Cbc0013I At root node, 1 cuts changed objective from -37772.749 to 
>> -37772.688 in 2 passes
>> Cbc0014I Cut generator 0 (Couenne convexifier cuts) - 1 row cuts 
>> average 2.0 elements, 320 column cuts (321 active)
>> Cbc0010I After 0 nodes, 0 on tree, 1e+50 best solution, best possible 
>> -37772.688 (777.18 seconds)
>> Cbc0010I After 100 nodes, 44 on tree, 1e+50 best solution, best 
>> possible -37739.148 (819.40 seconds)
>> Cbc0010I After 200 nodes, 93 on tree, 1e+50 best solution, best 
>> possible -37724.941 (835.35 seconds)
>> Cbc0020I Exiting on maximum time
>> Cbc0005I Partial search - best objective 1e+50 (best possible 
>> -37724.941), took 23515 iterations and 255 nodes (838.10 seconds)
>> Cbc0035I Maximum depth 80, 0 variables fixed on reduced cost
>>         "Not finished"
>> Stats: /tmp/at2730.nl   233 [var]    0 [int]  592 [con]  823 [aux]   
>> 1595 [root]     1595 [tot] 0.008999 [sep]  838.775 [time]  838.782 
>> [bb]        -3.772494e+04 [lower]
>> -3.562291e+04 [upper]     255 [nodes]
>>
>> couenne: Optimization interupted on limit.
>>
>> In the "Stats" line, a finite upper bound is being reported. However, 
>> just before exiting on maximum time, the "best solution" is +Inf.
>> The reported lower bounds are consistent in the two lines.
>>
>> What is going on here ?
>>
>> -- 
>> Regards,
>> Akshay
>> -- 
>> Akshay Gupte
>> Ph.D. student, Operations Research
>> School of Industrial & Systems Engineering
>> Georgia Institute of Technology
>> Email: akshayg at gatech.edu
>>
>>