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Hello,<br>
<br>
I am solving the linear relaxation of a problem with column
generation, and I wanted to try deleting columns in the solving
process, to reduce the size of the Master Problem and its solving
time (which seems to be the bottleneck for my problem).<br>
I tried to follow instructions reported in the documentation
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<a href="http://scip.zib.de/doc/html/FAQ.shtml#Q5.11">http://scip.zib.de/doc/html/FAQ.shtml#Q5.11</a>,
using the parameters "pricing/delvars and delvarsroot". I marked my
variables as deletable as well. Everything works, and as results I
get less columns at the end (which is normal), and in the process I
generate the same number of columns as without the delete, meaning
(I think) that only useless columns are deleted, which is also nice.
The weird part is that the solving time of the version with the
delete is bigger, and this increase is for solving the Master
Problem (the time for the pricer stays the same). So, I was
wondering from where this increase comes from. In theory as I delete
columns the Master is smaller, so it should be quicker to solve.<br>
Then I also tried to play with parameters "lp/colagelimit" and
"lp/cleanupcols and cleanupcolsroot", but changing their values does
not affect at all the solution time, the number of columns at the
end or the number of columns generated in the solving.<br>
<br>
Do you have any insight of this behavior or any suggestion I could
try?<br>
<br>
I would also like to know how the "deletevars" work, meaning which
is the criteria used to delete a variable?<br>
<br>
Thanks in advance,<br>
<br>
Alessia<br>
<br>
<br>
<pre class="moz-signature" cols="72">--
Alessia Violin
Service Graphes et Optimisation Mathématique (G.O.M.)
Université Libre de Bruxelles
C.P. 210/01
Boulevard du Triomphe
B-1050 BRUXELLES
Tel: 02 650 58 80 - Fax: 02 650 59 70
Email: <a class="moz-txt-link-abbreviated" href="mailto:aviolin@ulb.ac.be">aviolin@ulb.ac.be</a>
Webpage: <a class="moz-txt-link-freetext" href="http://homepages.ulb.ac.be/~aviolin/">http://homepages.ulb.ac.be/~aviolin/</a></pre>
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