[Symphony] Dramatic performance drop since 5.1.10

[Ted Ralphs]

This is unfortunate, but not actually too surprising. In 5.2, we added
features that were focused on solving the more difficult instances and
tuned our parameters to improve speed on those instances, but probably
neglected to ensure that performance on easier instances was not too
degraded. Thanks for the reminder :). What frequently happens when you
do parameter tuning on larger instances is that smaller instances
actually get slower as an unintended consequence. It's a difficult
balance to strike. Let us look at these and see if we can come up with
a better balance of improving performance on large instances without
degrading performance on smaller instances. In any case, it should be
relatively easy to replicate the performance of 5.1 with customized
parameter settings.

Chers,

Ted

On Thu, Sep 10, 2009 at 5:11 AM,  <Pierre.Lebodic at lri.fr> wrote:
> Hello,
>
> I've been using the C callbacks of Symphony 5.1.10 for a while and I
> recently tried updating to 5.2. On a batch of 80 test instances, I
> measured the run time of the updated solver. "Sys time" went from 2sec
> with 5.1 to 2m55sec with 5.2. As a comparison, cbc 2.3 takes 23sec. A
> little digging made me try with feasibility pump disabled, which roughly
> cut the sys time in two, but it's still nowhere close the previous
> version. I'd like to know if there are parameters that can be changed to
> get closer to how fast Symphony 5.1 performs. I'm solving 0-1 problems. I
> can provide MPS files if needed.
>
> The reason why I'm willing to switch to 5.2 is that I'm experiencing what
> seems to be a bug: when TM_gap_limit != -1, feasible solutions that don't
> respect the gap limit are produced. As far as I've been able to see, this
> bug seems to be fixed in 5.2. If you know about this bug, a quick edit in
> my 5.1 source would also do the trick.
> Thanks in advance
>
> Pierre Le Bodic
>
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-- 
Dr. Ted Ralphs
Associate Professor, Lehigh University
(610) 628-1280
ted 'at' lehigh 'dot' edu
coral.ie.lehigh.edu/~ted