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Dear Guillerme,<br>
<br>
you are right, SCIPsolveConcurrent tries to speed up the solving
process by using multiple cores. It does not parallelize the tree
search but runs the same instance multiple times in parallel with
different settings, communicates some global information between the
threads, and terminates when the first one is finished (in some
deterministic approximation of time).<br>
<br>
In order to use this, you need to compile one of the thread
processing interfaces (TPI) of SCIP, be default, none is built. You
can choose between TPI=tny (for TinyCThread, a portable
implementation of a subset of the C11 threads) or TPI=omp (for
OpenMP). If you compiled without TPI, the solve call for your
pricing problem probably returns with some error and I guess you do
not add a variable, which in the end causes the error you see
because SCIP does not have a variable to branch on but also no
optimally solved LP.<br>
<br>
I hope that helps, please write again if this does not fix the
issue.<br>
<br>
Best,<br>
Gerald<br>
<br>
<div class="moz-cite-prefix">On 11.04.2018 02:06, Guillerme Duvillié
wrote:<br>
</div>
<blockquote type="cite" cite="mid:20180411000610.GV19246@samus.home">
<pre wrap="">Dear all,
I'm a little bit puzzled about the difference between SCIPsolve and
SCIPsolveConcurrent. Based on what I understood, SCIPsolveConcurrent was
some sort of parallel implementation of SCIPsolve.
If this is the case, I experience something that seems weird to me. I'm
implementing branch and price algorithm for some special cases of
multidimensional affectation problems. When I use SCIPsolve to solve the
pricing problem, the resolution is really slow, the pricing is solved
over and over again and the general solution gets stuck to the
provided initial solution even after one hour of computations. On the
other hand, using SCIPsolveConcurrent returns the following error after
few miliseconds (and two pricing iterations):
[src/scip/solve.c:4503] ERROR: pricing was aborted, but no branching
could be created!
[src/scip/solve.c:4933] ERROR: Error <-10> in function call
[src/scip/scip.c:16231] ERROR: Error <-10> in function call
[src/scip/scipshell.c:100] ERROR: Error <-10> in function call
[src/scip/scipshell.c:392] ERROR: Error <-10> in function call
[src/cmain.c:162] ERROR: Error <-10> in function call
SCIP Error (-10): method returned an invalid result code
Snce I'm a SCIP beginner, the probability that I made a mistake in my
code is close to 1, but I cannot understand why switching from one
solving method to another returns such different answer.
Thank you in advance.
</pre>
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</pre>
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