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<div class="moz-cite-prefix">Hi Emily,<br>
<br>
it looks like in the second log file, no restart is performed at
all. As far as I can see in your code snippet, you did not
deactivate the pricer using SCIPdeactivatePricer(), but just
internally set a flag such that it always just returns.<br>
<br>
However, with an active pricer, restarts are not allowed, so SCIP
just does not do a restart ("number of runs" is 1) and just
continues solving. This was changed compared to the old mails you
are referencing. Therefore, you do not do presolving again, and if
you did not set the result pointer to SCIP_SUCCESS before
returning in the pricer while it is pseudo-deactivated, SCIP might
even not be able to use the node LP relaxation values as lower
bound (because your pricer returns SCIP_DIDNOTRUN by default,
meaning that there might still be improving columns and the dual
bound must not be used).<br>
<br>
The problem is that you are currently not allowed to deactivate a
pricer during solving. You could try to change this by changing
line 5048 in src/scip/scip.c from<br>
SCIP_CALL( checkStage(scip, "SCIPdeactivatePricer", FALSE,
TRUE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE,
FALSE, TRUE, FALSE, FALSE) );<br>
to<br>
SCIP_CALL( checkStage(scip, "SCIPdeactivatePricer", FALSE,
TRUE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, TRUE,
FALSE, TRUE, FALSE, FALSE) );<br>
(set the fifth-last parameter to TRUE). However, I'm not
completely sure if deactivating a pricer during solving may
corrupt internal data structures.<br>
<br>
If you run into any troubles after the change, please try the
following:<br>
In src/scip/solve.c lines 3605 and 3609, change <br>
"set->nactivepricers == 0" to "(set->nactivepricers == 0 ||
stat->userrestart)".<br>
<br>
This will allow a user restart even if pricers are active. Then,
you need to follow the advice given in the old mail and implement
the exitsol callback to change the modifiable flags and deactivate
your pricer.<br>
<br>
Best,<br>
Gerald<br>
<br>
On 01.09.2015 17:50, Aao Du wrote:<br>
</div>
<blockquote
cite="mid:CAEa_GvO4BPk2+uE_YjAyj_Ndnj9Ry2AvHOqgv2QhPihZ7faTQQ@mail.gmail.com"
type="cite">
<div dir="ltr">
<div>
<div>Hi Jakob,<br>
</div>
<div><br>
</div>
I have attached the log files. For the instance solved by the
first method, the log file is for the second part of the
solving process where the final master problem is fed to SCIP.
(So the time does not include the root node time)<br>
For the instance solved by the second method, the solving time
does include the root node time (which is around ~100
seconds).<br>
</div>
<div>Note that in larger instances. the difference become more
significant. <br>
</div>
<div><br>
</div>
<div>Just to check whether the way I am doing is correct. In the
scip_redcost method, I have the following code lines at the
beginning: <br>
</div>
<div>if(SCIPgetDepth(scip) == 1)<br>
</div>
<div> Change the modifiable flag of the constraints, and<br>
SCIPrestartSolve(scip)<br>
</div>
<div> isrestart = true; (isrestart is a pricer variable
which is initialized to false) <br>
</div>
<div> return SCIP_OKAY<br>
</div>
<div>if (isrestart)<br>
</div>
<div> return<br>
<br>
<br>
</div>
<div>In the previous emails, it was instructed to change the
flag of constraints at the scip_exitsol method, but that
method is not entered until the mixed integer master problem
is solved optimally. So trying that did not work either. (<a
moz-do-not-send="true"
href="http://listserv.zib.de/pipermail/scip/2011-September/000754.html"><a class="moz-txt-link-freetext" href="http://listserv.zib.de/pipermail/scip/2011-September/000754.html">http://listserv.zib.de/pipermail/scip/2011-September/000754.html</a></a>)<br>
</div>
<div><br>
</div>
<div>Emily<br>
</div>
<br>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Tue, Sep 1, 2015 at 3:41 AM, Jakob
Witzig <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:witzig@zib.de" target="_blank">witzig@zib.de</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">Hi Emily,<br>
<br>
probably the presolving in the second case is finished
earlier because [i] presolving after a restarts is reduced
(but I'm not sure) [ii] the presolver itself remember that
they could not find anything (because your constraints were
modifiable) and they do not run.<br>
<br>
If you want, you can send me your two log-files and I will
have a look at it.<br>
<br>
Best,<br>
Jakob<span class=""><br>
<br>
On 08/31/15 15:57, Aao Du wrote:<br>
</span>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex"><span
class="">
Hi Jacob,<br>
<br>
I believe I did not explain my question well. Here are
the two methods I<br>
have tried:<br>
1) Solve the master problem at the root node. Change the
variables type<br>
and write it as an lp file.Then solve the MIP separately
with SCIP.<br>
2) Define the variables as integer from the beginning.
After the root<br>
node, restart the scip and change the modifiable flag of
constraints.<br>
<br>
Now these two methods solve in two significantly
different solution<br>
time. From the log files, I figured the number of
variables in the final<br>
master problem is decreased in the first method after
presolving by<br>
SCIP. However, in the second method, after the scip is
restarted(which I<br>
think does the presolving too), the number of variables
stay the same.<br>
I would appreciate if you can help me figure out the
reason<br>
<br>
Thanks,<br>
Emily<br>
<br>
On Mon, Aug 31, 2015 at 4:19 AM, Jakob Witzig <<a
moz-do-not-send="true" href="mailto:witzig@zib.de"
target="_blank"><a class="moz-txt-link-abbreviated" href="mailto:witzig@zib.de">witzig@zib.de</a></a><br>
</span>
<div>
<div class="h5">
<mailto:<a moz-do-not-send="true"
href="mailto:witzig@zib.de" target="_blank">witzig@zib.de</a>>>
wrote:<br>
<br>
Hi Jens,<br>
<br>
what do you mean was 'differ in the results'? Only
solving time and<br>
nodes? The problem is, that the variable order can
change if you<br>
write the problem is an lp file. You can try to
write your problem<br>
as an mps or cip file.<br>
<br>
If you want, you can send me the log-files
including the statistics<br>
of the two solves (1: copy into a subscip, 2:
write as an lp and<br>
solve separately) and I will have a look on it.<br>
<br>
Best,<br>
Jakob<br>
<br>
<br>
On 08/31/15 08:33, Jens Leoff wrote:<br>
<br>
Hi,<br>
<br>
I also tried to write a heuristic to solve my
Branch & Price<br>
problem as<br>
Price & Branch. I tried to copy the node
problem to a subscip<br>
where I<br>
change the constraints to be non-modifiable.
Apart from that the<br>
scips<br>
differ in what plugins are included (no
pricer, but e.g.<br>
separators).<br>
However, I also wasn't able to produce the
same results this way<br>
as one<br>
can obtain by writing the node problem as a
MIP and solving this<br>
separately with scip.<br>
<br>
I guess this kind of heuristic would be
interesting for lots of<br>
Branch &<br>
Price applications.<br>
So, I would like to know how to do this
properly as well.<br>
<br>
Best,<br>
<br>
Jens<br>
<br>
<br>
</div>
</div>
<div>
<div class="h5">
On <a moz-do-not-send="true"
href="tel:31.08.2015%2008" value="+13108201508"
target="_blank">31.08.2015 08</a>
<tel:31.08.2015%2008>:06, Jakob Witzig wrote:<br>
<br>
Hi Emily,<br>
<br>
you can use the method SCIPvarChgType to
convert the<br>
variables into<br>
integers, but the method can only be
called if the variables<br>
are not<br>
part of the problem, e.g., before you call<br>
SCIPtransformProb. Do you<br>
use sub-SCIPs to solve your subproblems?
If yes, than you<br>
can call the<br>
method mentioned above before you start
solving the subproblem.<br>
<br>
I don't get the connection between your
two ways. Why is<br>
changing the<br>
variables and changing the modifiability
flag of the constraint<br>
equivalent?<br>
<br>
If you restart your problem SCIP tries to
transform cuts<br>
into globally<br>
valid constraints and will fix all
variables that have equal<br>
global<br>
upper and lower bounds, i.e., the
variables can removed from the<br>
problem. Hence, if you could not tighten
the bounds of your<br>
variables<br>
enough or you didn't found global valid
cuts a restart<br>
directly after<br>
the root will give you the same problem as
before.<br>
<br>
I think changing the flags of a constraint
should be done<br>
before you<br>
start solving your subproblem.<br>
<br>
Best,<br>
Jakob<br>
<br>
<br>
On 08/31/15 04:38, Aao Du wrote:<br>
<br>
Dear all,<br>
<br>
I have a decomposed model, a master
problem and<br>
subproblems. I am trying<br>
to perform pricing only at the root
node, and then<br>
change the variables<br>
to integer and solve it again. I have
tried two ways.<br>
One is to print<br>
the lp format of the problem after
root node, with<br>
variables as integer,<br>
and give it to SCIP binaries. In this
way, the second<br>
part of the<br>
solving process ( solving the final
master problem with<br>
binaries) is<br>
performed fast.<br>
The other way, is to define the
variables as integer<br>
from begining, and<br>
stop pricing at the root node, and
change the constarints to<br>
unmodifiable. In this way, after the
lp of master<br>
problem is solved, it<br>
takes way more than the first method
to solve it.<br>
Following a previous<br>
email, I tried to restart the master
problem after root<br>
node, but it did<br>
not make any change in the time. I
thought maybe i am<br>
doing sth wrong.<br>
What is the proper place in the
pricerobj to change the<br>
modifiable flag<br>
of constraints? I think it should be
somewhere before<br>
redcost, or maybe<br>
in it.<br>
<br>
Sorry for the long email.<br>
<br>
Thanks,<br>
Emily<br>
<br>
<br>
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<div class="HOEnZb">
<div class="h5">
<br>
<br>
-- <br>
Jakob Witzig<br>
<br>
Konrad-Zuse-Zentrum für<br>
Informationstechnik Berlin (ZIB)<br>
<br>
Division Mathematical Optimization and Scientific
Information<br>
Research Group Mathematical Optimization Methods<br>
<br>
Takustrasse 7<br>
14195 Berlin<br>
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value="+493084185416" target="_blank">+49 (0)30
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