<div dir="ltr"><div><div>Dear Gerald,<br><br></div>thank you for you response. <br><br><br></div><div>About 2) yes, I am sure that pricing is performed at this node, and 3) I start the B&P with a with a set of initial variables that gives a feasible primal solution to the integer problem. Both, initial and priced variables are marked as removable and all constraints are marked as modifiable. <br><br>About 1), I think this could be actually the problem. I do not compute the lower bound at any point. I just followed the binpacking example to create my own implementation but I missed this issue. In fact, I also noticed that whenever an integer LP solution gets into the pricing callback, scip do not update the best upper bound in case of promising one. I read a previous email about this issue and recommended to use SCIPupdateCutoofbound() and/or SCIPsetObjlimit(). However, what I am more concerned about why this integral and feasible solution is not stored as a Primal bound of the original Integer Master Problem thant setting a new cuttoffbound. If you can help me explaining me a little bit more about this because I'm find myself quite lost with that.<pre></pre><br></div><div>Best regards,<br></div><br><div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">2015-03-04 19:35 GMT+01:00 Gerald Gamrath <span dir="ltr"><<a href="mailto:gamrath@zib.de" target="_blank">gamrath@zib.de</a>></span>:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
Dear Christina,<br>
<br>
sorry for the late reply, but we were quite busy in the last weeks.<br>
<br>
There might be different reasons for this behavior.<br>
<br>
1) Does your pricing callback compute a lower bound and sets the
lowerbound pointer accordingly? If this is higher than the cutoff
bound, the node will be cut off.<br>
<br>
2) Perhaps the propagation already detected infeasibility? Are you
sure that you perform pricing at this node?<br>
<br>
3) Are all your variables created by pricing and all constraints
marked to be modifiable? Otherwise, the enforcement might also
detect infeasibility of an unmodifiable constraint.<br>
<br>
Best,<br>
Gerald<br>
<br>
<div>Am 19.02.2015 um 15:27 schrieb Cristina
Núñez del Toro:<br>
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<div>
<div>Dear all,<br>
<br>
</div>
I am currently implemented a Branch&Price
algorithm. For my problem, I have 3 types of
variables, say "x","y" and "z". I have just finished
my on branching rule that implies to only branch on
the "z" variables. Apparently, everything goes ok; I
mean, everytime SCIP enters to the branchexeclp
routine, it looks for the most fractional "z"
variable and do branch on it. However, I have
noticed that a certain point of the algorithm, after
finishing the pricing loop, SCIP "skips" (sorry for
the joke) the branching phase (the node is cutted
off/pruned), I mean, it does not enter to any
branching callback method and goes directly to the
handler constraint to propagate another node. As far
I understand, this would be of course a normal
behaviour if, after finishing the pricing stage :<br>
<br>
</div>
a) the objective value of the current LP is greater or
equal than the incumbent,<br>
b) the current LP solution is an integer solution,<br>
</div>
c) the current LP solution is an integer solution and it
is optimal.<br>
<br>
</div>
However, I found a pruned node with a fractional LP
solution (inluding some "z" variables with fractional
value) but with the objective value <span lang="en"><span>strictly lower than
the incumbent.<br>
<br>
</span></span></div>
<span lang="en"><span>Is
there any reason for expecting this? <br>
<br>
</span></span></div>
<span lang="en"><span>Thanks
in advances,<br>
<br>
</span></span></div>
<span lang="en"><span>Best
regards,<br>
</span></span>
<div>
<div>
<div>
<div>
<div>
<div>
<div>
<div><br>
<br>
-- <br>
<div>---<br>
Cristina Nuñez<br>
</div>
</div>
</div>
</div>
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</div>
</div>
</div>
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<br>
<fieldset></fieldset>
<br>
</div></div><pre>_______________________________________________
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</pre>
</blockquote>
<br>
</div>
</blockquote></div><br><br clear="all"><br>-- <br><div class="gmail_signature">---<br>Cristina Nuñez<br></div>
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