<div dir="ltr"><div><div>Hello Gerald,<br><br><br>I have revised the initial parameters settings and, as
you said, I had the heuristic as disabled (and also the separating and
presolving). Now, the heuristic is not disabled but the separating and
presolving. I'm sending you the statistics file. I'm not using the
runshell SCIP command line interface, so I don't know where can obtain
the log file. Is there another way to obtain it without including the
SCIP command line?<br><br></div><div>What I have discovered is that the initial cutoff bound (3.0001) is lower than my (already known) optimal value (3.2). So, even the LP gets an integer solution with value of 3.2, scip never takes this bound into account. I have already checked my code and I never set this cutoff bound, so I suspect this 3.0001 is set by scip from the very beginning. In fact, I have tried starting the B&Price with different initial columns. Even if the initial columns yields feasible or infeasible solution, the cutoff bound is always 3.0001 after finding the first feasible LP solution. You may think that I have something wrong in my problem definition and that 3.2 is actually not my optimal solution, but the same cutoff bound of 3.0001 appears even when the initial columns gives a integer (and obviously feasible) LP solution with value equal to 3.2. It is somehow normal?<br></div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">2015-03-09 18:43 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">
<div>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<div><div class="h5"><br>
<br>
On 06.03.2015 17:08, Cristina Núñez del Toro wrote:<br>
</div></div></div><div><div class="h5">
<blockquote type="cite">
<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.<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>
</div>
<blockquote type="cite">
<div>
<div>
<div dir="ltr">
<div>
<div>
<div>
<div>
<div>
<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>
</div>
</div>
</div>
</div>
</div>
</div>
<br>
<fieldset></fieldset>
<br>
</div>
</div>
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</pre>
</blockquote>
<br>
</div>
</blockquote>
</div>
<br>
<br clear="all">
<br>
-- <br>
<div>---<br>
Cristina Nuñez<br>
</div>
</div>
</blockquote>
<br>
</div></div></div>
</blockquote></div><br><br clear="all"><br>-- <br><div class="gmail_signature">---<br>Cristina Nuñez<br></div>
</div>