[SCIP] Long runtimes of VRP solver

[Shen Li]

Thanks a lot for the prompt and helpful response, Gerald!

Best
Shen

> On 31 Jan 2019, at 08:49, Gerald Gamrath <gamrath at zib.de> wrote:
> 
> Dear Shen,
> 
> don't worry, nothing went wrong, this is similar to the behavior I observed.
> 
> Note that the VRP example is just a very basic example for how a pricer can be implemented. It does not focus on providing good performance since this would complicate the code. If you want to implement a branch-and-price code, I would always recommend to look at the binpacking example or the coloring application. These two provide a better overview of what is normally needed for branch-and-price code, including problem data and a dedicated branching rule.
> 
> Best regards,
> Gerald
> 
> On 30.01.19 11:51, Shen Li wrote:
>> Dear SCIP mailing list
>> 
>> I just compiled the VRP example of the SCIP package, and I obtained the following output for eil22.vrp (part of the SCIP/VRP data files):
>> 
>> (…)
>>  time | node  | left  |LP iter|LP it/n| mem |mdpt |frac |vars |cons |cols |rows |cuts |confs|strbr|  dualbound   | primalbound  |  gap   
>> (…)
>>   428s|   300 |    15 |554079 |1689.8 | 256M|  20 |  29 |  37k| 273 |  13k| 273 |   2 |   0 | 421 | 3.687105e+02 | 3.750000e+02 |   1.71%
>> 
>> SCIP Status        : problem is solved [optimal solution found]
>> Solving Time (sec) : 476.24
>> Solving Nodes      : 359
>> Primal Bound       : +3.75000000000000e+02 (23 solutions)
>> Dual Bound         : +3.75000000000000e+02
>> Gap                : 0.00 %
>> SCIP Status        : problem is solved [optimal solution found]
>> Total Time         :     476.24
>>   solving          :     476.24
>>   presolving       :       0.00 (included in solving)
>>   reading          :       0.00
>>   copying          :       0.06 (3 #copies) (minimal 0.02, maximal 0.03, average 0.02)
>> (…)
>> 
>> I found it surprising that it took 428 seconds to solve this instance, which is typically solved within fractions of a second. Is this is similar to the behaviour you have observed? If not, any pointers to where I may have gone wrong would be greatly appreciated!
>> 
>> Many thanks
>> 
>> Shen
>> 
>> 
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