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Dear Diego,<br>
<br>
I don't really see a difference to your previous question (see
below) for which you already received an answer by Gerald. Please
let me know if I miss something.<br>
<br>
<br>
Cheers,<br>
<br>
Benny<br>
<br>
<br>
<div class="moz-cite-prefix">On 03/22/2016 11:30 AM, <a class="moz-txt-link-abbreviated" href="mailto:dponce@us.es">dponce@us.es</a>
wrote:<br>
</div>
<blockquote cite="mid:e07300280d1b3f4f822afbe920753841@us.es"
type="cite">
<p>Hello SCIP,</p>
<p>I have implemented the stabilization method described by Pessoa
et al on a column generation framework. Among the algorithm,
sometimes there is not variable added (what doesn't mean that
the pricing finishes), so to avoid that SCIP "think" the
optimality is reached, I add a phantom variable on this step. </p>
<p>Is it necessary?</p>
<p>I there a better way to do that?</p>
<p>Thanks in advance.</p>
<p>Best.</p>
<p>Diego. </p>
</blockquote>
<br>
<div class="moz-cite-prefix">On 04/24/2015 10:49 AM, Gerald Gamrath
wrote:<br>
</div>
<blockquote cite="mid:553A038F.9030806@zib.de" type="cite">
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http-equiv="Content-Type">
<div class="moz-cite-prefix">Dear Diego,<br>
<br>
you are right, you need to handle the case of a misprice
explicitly. If your pricer finishes without adding variables
(and your result pointer is set to SUCCESS), SCIP will assume
that there are no improving variables and use the current LP
value as a dual bound.<br>
<br>
This means, whenever you are not sure if there are more
improving variables, you should set the result pointer to
DIDNOTRUN and SCIP won't use the LP value as dual bound. On the
other hand, it will stop pricing and perform branching, which
you do not want to do either.<br>
<br>
Therefore, your pricer should just handle this case. If it
performed pricing with smoothed dual values and does not find an
improving variable, it should just perform another round of
pricing (without returning from the PRICERREDCOST callback). In
this round, you either adjust your alpha to give a higher weight
to the original dual values or just use those alone and perform
exact pricing without smoothed duals.<br>
<br>
Best,<br>
Gerald<br>
<br>
On 21.04.2015 12:50, <a moz-do-not-send="true"
class="moz-txt-link-abbreviated" href="mailto:dponce@us.es">dponce@us.es</a>
wrote:<br>
</div>
<blockquote cite="mid:2ab1e2bacf7a8ccaa7b65e4546f721f3@us.es"
type="cite">
<p>Hello list,</p>
<p>as part of a Branch-and-Price procedure, I'd like to apply
stabilization in order to add less variables at the end to
check optimality. As I readed in another thread, smoothing
approach (Pessoa et al.) is a good option in SCIP.</p>
<p>I have it implemented, but it avoids correct solutions. I
think the problem is the following: when a misprice (there are
columns to add but the pricing do not provide such columns
using the convex combination) happens, the pricing detect that
no variables were added and SCIP go out the pricing before
time. How could I deal whith this problem?</p>
<p>Thanks in advance.</p>
<p>Diego.</p>
<p> </p>
<div> </div>
<br>
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<pre class="moz-signature" cols="72">--
______________________________
Benjamin Müller
Zuse Institute Berlin
Takustr. 7, 14195 Berlin
<a class="moz-txt-link-abbreviated" href="mailto:benjamin.mueller@zib.de">benjamin.mueller@zib.de</a>
+49 30 841 85-195</pre>
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