[SCIP] How to deactivate aging and avoid scip internal pricer ?

[Sandra Ulrich Ngueveu]

Hello Gerald,

Thank you very much for your reply.

The model is small (302 variables).

Setting parameter age limit to -1 does not seem to deactivate scip 
internal pricing (442 variables from our pricing versus 66334 from scip).

Also, let me specify that at the beginning of each pricing 
phase///PRICERREDCOST, /we displayed the number of variables previously 
added by our pricer and the result of SCIPgetNPricevarsFound. During 
several iterations, the two numbers were the same. But at some point the 
second number becomes higher than the first, and the difference between 
the two numbers increases until the end of the branch-and-price.

The statistics displayed at the end (with scipprintstatistics) showed 
that scip's pricer is very fast (0.03s), so we not longer expect to gain 
any speed-up there.

But we would still like to deactivate it if possible, to help us 
investigating the following issue : Let's consider two disjoint sets of 
columns S1 and S2, and their union Sall (= S1 U S2). We are trying to 
understand why in our branch-and-price, adding Sall leads to a worse 
final solution than adding S1 example. Therefore we are carefully 
rechecking our code and we would like to deactivate scip's pricer if 
possible.

Best regards,

Sandra


Le 25/06/2018 à 19:19, Gerald Gamrath a écrit :
> Dear Sandra,
>
> I don't think that SCIPgetNPricevarsFound returns what you are 
> interested in. As far as I can see, this is the total number of 
> variables that were added to the to the pricestore. This may be 
> variables "priced" by SCIP, but also the variables you priced, as well 
> as all variables in your original formulation, that go through the 
> pricestore once to enter the LP. Perhaps your original formulation is 
> quite large?
>
> Setting the age limit to -1 should normally do the trick. There are 
> other things like "lp/cleanupcols(root)", but those are disabled by 
> default.
>
> When you look at the statistics after solving ("disp stat" in the 
> interactive shell or SCIPprintStatistics()), you should see how many 
> variables are really added by your pricer and by the internal SCIP 
> pricing ("problem variables").  Is there a nonzero number for the latter?
>
> Best,
> Gerald
>
> On 25.06.2018 18:28, Sandra Ulrich Ngueveu wrote:
>> Hello,
>>
>> We are doing a Branch-and-Price with SCIP. Using function 
>> "SCIPgetNPricevarsFound", we realized that a very higher number of 
>> variables were "priced" by scip, compared to the number of columns 
>> that we explicitely added (127253 instead of 475).
>>
>> We would like to deactivate such internal pricing (which according to 
>> some forum is related to column aging) just to verify if the code 
>> would be faster for our specific problem. We tried setting parameter 
>> lp/colagelimit to -1, but the number of additional pricedvars 
>> declared by scip remained unchanged.
>>
>> Could you please tell us if there is another parameter we could 
>> activate or deactivate to achieve the desired behaviour ?
>>
>> Best regards,
>>
>> Sandra U. Ngueveu
>>
>

-- 

Maître de Conférences / Associate Professor
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Equipe ROC
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