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<div class="moz-cite-prefix">Dear Emiliy,<br>
<br>
</div>
<blockquote
cite="mid:CAEa_GvPuWk7uECOseGaMpYxpfAQ9O4Fix7VchZJP+T48hqo90Q@mail.gmail.com"
type="cite">I made the change to the SCIPdeactivatepricer. Now
based on the statistics, restarting is performed and there are 2
runs. However, compared to the method 1, it is still slower. What
I see in the first method,s logfile, there are several round of
presolving performed and several runs(which I think it means
aeveral restarts happen?). It looks to me the second method does
only the first round of presolving that is performed in method 1.
Is there a reason to expect this? I could not figure if there is
any parameter that I need to adjust in oreder to have several
restarts?</blockquote>
Indeed, the effect of the first restart is measured (in terms of
fixed variables) and more restarts are only allowed if at least 10%
of the variables were removed. It may be that this is not the case
for the restart you trigger and thus, no second restart will be
performed. You can change the parameter "presolving/restartminred"
to adjust this behaviour, e.g., just set it to 0.0 to see if another
restart is then performed.<br>
<br>
If there is still a significant difference afterwards, please send
us the log files again. If you do so, please include also the SCIP
output during solving.<br>
<br>
<blockquote
cite="mid:CAEa_GvPuWk7uECOseGaMpYxpfAQ9O4Fix7VchZJP+T48hqo90Q@mail.gmail.com"
type="cite">
<div class="gmail_extra"><br>
</div>
<div class="gmail_extra">Also, i am changing the modifiable flags
and deactivating pricer in the redcost method. Doing it in the
exitsol method did not perform restrating as it enters the
exitsol method only when the whole problem is solved. I am not
sure if this is what is supposed to happen.</div>
</blockquote>
<br>
Did you change the lines in solve.c? Without this, the restart will
not be triggered. If a restart is triggered, the exitsol method
should be called, so that you can disable the pricer and mark the
constraints unmodifiable.<br>
<br>
<br>
Best,<br>
Gerald<br>
<br>
<blockquote
cite="mid:CAEa_GvPuWk7uECOseGaMpYxpfAQ9O4Fix7VchZJP+T48hqo90Q@mail.gmail.com"
type="cite">
<div class="gmail_extra"><br>
</div>
<div class="gmail_extra">Thanks in advance,</div>
<div class="gmail_extra"><br>
</div>
<div class="gmail_extra">Emily<br>
<div class="gmail_quote">On Tue, Sep 1, 2015 at 1:35 PM, Gerald
Gamrath <span dir="ltr"><<a moz-do-not-send="true">gamrath@zib.de</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
<div>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
<div>
<div><br>
<br>
On 01.09.2015 17:50, Aao Du wrote:<br>
</div>
</div>
</div>
<blockquote type="cite">
<div>
<div>
<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"
target="_blank">http://listserv.zib.de/pipermail/scip/2011-September/000754.html</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"><a class="moz-txt-link-abbreviated" href="mailto:witzig@zib.de">witzig@zib.de</a></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><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> 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">witzig@zib.de</a><br>
</span>
<div>
<div> <mailto:<a moz-do-not-send="true">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> 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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<br>
--<br>
Jakob Witzig<br>
<br>
Konrad-Zuse-Zentrum für<br>
Informationstechnik Berlin (ZIB)<br>
<br>
Division Mathematical Optimization and
Scientific Information<br>
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<div>
<div> <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>
<br>
Tel. : <a moz-do-not-send="true"
href="tel:%2B49%20%280%2930%2084185-416"
value="+493084185416" target="_blank">+49
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Fax : <a moz-do-not-send="true"
href="tel:%2B49%20%280%2930%2084185-269"
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