[Lemon-user] performance of network simplex on instance i_n13

[Matthew Galati]

       $ ./tools/dimacs-solver -double i_n13.dimacs.int
>        Run NetworkSimplex: u: 3.46s, s: 242.48s, cu: 0s, cs: 0s, real:
> 247.726s
>
>        Feasible flow: found
>        Min flow cost: 8.47715e+11
>
> It is 247, but only 3.4s in the userspace??? First I said, no, the user
> and system times must have been changed. But I checked the related code
> and couldn't find any bug.
>
>
On my machine (linux/g++), user time matches real time for this instance.
This is giving the correct solution - and seems to take long (relative to
other solvers).






> Secondly, if I use -int or -long, it runs basically in 0s and gives a
> feasible solution, but a wrong one (Min flow cost: 137). I guess, the
> reason is that the demand is given in a floating point form (9.03353e
> +06). I would at least expect a format error message in this case.
>

I don't think the reader checks for this - so it is probably just treating
it as int or long and truncating - causing the wrong objective.






Thirdly, I replaced the demand to integer format (9033530), and rerun
> "./dimacs-solver -long". It says: "Feasible flow: not found". Why?
>


My guess would be an overflow here.
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