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<div class="moz-cite-prefix">Dear Christina,<br>
<br>
it should not be a problem if you do not set a lowerbound. Just to
be sure, you could set it to -SCIPinfinity().<br>
<br>
So we will need to investigate your problem further. Could you
send me a log file (including statistics)?<br>
<br>
About the integer LP solutions: This should automatically be done
by the simplerounding heuristic. Did you perhaps disable the
heuristic by accident?<br>
<br>
Best,<br>
Gerald<br>
<br>
On 06.03.2015 17:08, Cristina Núñez del Toro wrote:<br>
</div>
<blockquote
cite="mid:CAKuRvOHv6MUJitKvi4xWbMOQGUcDFXeMEjizqJxt7skN0mUw5A@mail.gmail.com"
type="cite">
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<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.<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 moz-do-not-send="true"
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>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>
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<br>
<br clear="all">
<br>
-- <br>
<div class="gmail_signature">---<br>
Cristina Nuñez<br>
</div>
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