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Dear Andreas,<br>
<br>
sorry for the late reply. I can understand your point of view and I
also had to think twice in order to find a possible explanation for
this behavior. You are right that just calling a pricer which
returns SCIP_SUCCESS and does not add any variables should not
change the solver behavior. However, already the fact that there is
an active pricer changes the behavior of SCIP, because some
reductions, e.g., in propagation, can only be performed if the model
description is fully present already. Therefore, if a pricer is
present, some components of SCIP are disabled, which may lead to the
differences you were observing.<br>
<br>
Best,<br>
Gerald<br>
<br>
<div class="moz-cite-prefix">On 15.04.19 13:56, Linß, Andreas wrote:<br>
</div>
<blockquote type="cite"
cite="mid:a55e64ad0f024396a0a039ec562608e4@uni-kassel.de">
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<p><span id="ms-rterangepaste-start"></span></p>
<p><span>Dear SCIP Community,</span></p>
<p><span><span>I am currently working on a Branch and Price
algorithm with SCIP and the C++ interface</span> with
</span><span>SCIP version 6.0.1. <span>I've noticed the hints
and the VRP example and implemented the callback
functions. So<span> my pricer returns *result
=SCIP_SUCCESS when it has found a new variable, or it
could prove that no more variables with negative reduced
cost exists. I am solving my problem with the following
settings:<br>
</span></span></span></p>
<div>SCIP_CALL( SCIPsetHeuristics
(scip,SCIP_PARAMSETTING_OFF,true));<br>
SCIP_CALL( SCIPsetSeparating
(scip,SCIP_PARAMSETTING_OFF,true)); <br>
</div>
<div>
<div> SCIP_CALL( SCIPsetLongintParam(scip,"limits/nodes",
2000));<br>
SCIP_CALL( SCIPsetIntParam(scip,"pricing/maxvars",10000));</div>
<div><br>
</div>
<div><span>I stoped the solution process for comparability
after 2000 Branch and Bound nodes</span>.</div>
<div><br>
</div>
<div>With a pricer, which have to generate the variables, i
have 11.227 dual Lp calls and 2027 primal LP calls with 2902
own_pricer calls with 1201 generated variables.
<br>
</div>
<div>With a problem with all variables an a pricer, that can
not generate variables, i have 9273 dual calls and 2001
own_pricer calls, with 0 generated variables.
<br>
</div>
<div>With a full problem with all variables an no pricer, i
have <span>2837</span> dual LP calls.
<br>
</div>
<div><br>
</div>
<div>The variables of case 1 and case 3 are generated the same
way. The only difference of these cases is the possibility
to use a pricer, that only returns SCIP_SUCCESS.
<br>
</div>
<span>So it is confusing, that the solver, with the pricer,
calls dual LP more often than without, although the pricer
does nothing.
<br>
I thought, that the LP is solved with the existing variables
of memory and model and after that, the pricing is called.
The pricing can not improve the model, so the LP should not
be touched again. But my way of thinking does not explain
the difference of 2837 and 9273 calls. <br>
</span></div>
<div><span><br>
</span></div>
<div><span>I am searching for an explanation, why the dual LP
is called more often, when I am activating my own pricer.
<br>
</span></div>
<div><span>Also I hope, that you understand my point of view <span>and
I hope you have an explanation for this phenomenon.</span><br>
</span>
<div><br>
</div>
<div><br>
</div>
<span><span></span></span></div>
<span><span>Nice regards<br>
Andreas</span></span><span id="ms-rterangepaste-end"></span><br>
</div>
<br>
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