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Dear Feng,<br>
<br>
please note that the master consists of (continuous) tour and
(integral) arc variables. This brings the advantage that it is
sufficient to branch on the arc variables only. Of course, you can
formulate the master problem without arc variables but then you need
integrality requirements on the tour variables. This brings the
problem that branching on the tour variables changes the nature of
the pricing problem and thus it is not solvable with the help of
dynamic programming anymore.<br>
<br>
In contrast to this, branching on the arc variables does not really
change the pricing problem. y_e = 0 just removes edge e from the
graph you use to search for the tour with the most negative reduced
cost. y_e = 1 does not change anything.<br>
<br>
Write me a personal mail if you have more questions about the VRP
example.<br>
<br>
<br>
Best regards,<br>
<br>
Benny<br>
<br>
<br>
<div class="moz-cite-prefix">On 04/01/2015 02:39 PM, Feng Gao wrote:<br>
</div>
<blockquote
cite="mid:CAEptEzVoJe6GphWdyjj2dV1YQzE353tmF+df_PyaoA6-fBofaA@mail.gmail.com"
type="cite">
<div dir="ltr">Dear all,
<div><br>
</div>
<div>Is there anybody familiar with the VRP example in SCIP? </div>
<div>When the pricer find a tour with negative reduced cost, why
was the column added back in the form of arc variable? Is the
problem in the main program master problem or original
problem? If it is master problem, adding back arc variable
does not make sense.</div>
<div><br>
</div>
<div>Sorry if this is a rather easy question. But I heard that
the problem should be the master problem in the main program.</div>
<div><br>
</div>
<div>Best regards,</div>
<div><br>
</div>
<div>Feng Gao</div>
</div>
<br>
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<br>
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</pre>
</blockquote>
<br>
<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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