<div dir="ltr"><div><div>Hello again,<br><br></div>I have already solve the problem! Because following binpacking example, I just left SCIPsetObjIntegral() without noticed that my solution does not fullfill this condition. Now, I obtain the optimal value of 3.2 recognized. However, SCIPgetOrigObjscale() and SCIPgetTransObjscale() are still 0 and 1, respectivelly. Should I expect both values equal to 1 ?<br><br></div>Thanks for all,<br></div><div class="gmail_extra"><br><div class="gmail_quote">2015-03-10 17:52 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>Hi Christina,<br>
<br>
</div><span class="">
<blockquote type="cite">
<div dir="ltr">
<div>
<div>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>
</div>
</div>
</div>
</blockquote></span>
But you get output lines from SCIP don't you? Just pipe them to some
file and send this to me.<span class=""><br>
<br>
<blockquote type="cite">
<div dir="ltr">
<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>
</div>
</div>
</blockquote></span>
Do you activate your pricer before calling SCIP solve? If not, SCIP
might detect that the objective value of each solution will always
be a multiple of some number, for example 0.2. In that case, if a
solution with value 3.2 was found, SCIP would set a cutoff bound of
3.0 + eps, which would be exactly 3.0001. But this should not happen
if a pricer is enabled. Perhaps you can check that
SCIPgetOrigObjscale() and SCIPgetTransObjscale() are both 1.0.<br>
<br>
Best,<br>
Gerald<div><div class="h5"><br>
<br>
<blockquote type="cite">
<div dir="ltr">
<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><br>
<br>
On 06.03.2015 17:08, Cristina Núñez del Toro wrote:<br>
</div>
</div>
</div>
<div>
<div>
<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>---<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>