Re: [eigen] Getting started / Compiling and running your first program

[Thomas Klimpel <jacques.gentzen@xxxxxxxxx>]

I agree that link to this:
http://eigen.tuxfamily.org/index.php?title=FAQ#How_do_I_get_good_performance.3F

is better than a complicated command line which includes -NDEBUG


How about an example with nice debug compile flags instead?

g++ -I /path/to/eigen/ my_program.cpp -o my_program -g -Og

This will already eliminate the biggest speed disadvantages, and will
be easier to debug, especially for the beginner (which is implicitly
addressed here).

Regards,
Thomas

On Thu, Jan 31, 2019 at 10:35 PM Christoph Hertzberg
<chtz@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> I agree on that we could/should mention that for good performance
> Eigen-code should be compiled with something like `-O2 -DNDEBUG
> -march=native` (`-mtune` is implied by `-march`). Or link to this:
> http://eigen.tuxfamily.org/index.php?title=FAQ#How_do_I_get_good_performance.3F
>
> I would however strongly discourage compiling with `-DNDEBUG` until you
> tested your code for correctness, since this prevents several trivial
> beginner mistakes (or rather exposes them). We actually also have quite
> a few questions/"bug reports" about unexpected behavior which was in
> fact caused by some wrong usage.
>
> Christoph
>
>
>
> On 31/01/2019 18.30, Thomas Klimpel wrote:
> > Hi,
> >
> > http://eigen.tuxfamily.org/dox/GettingStarted.html
> >
> > in section
> > Compiling and running your first program
> > suggests
> >
> > g++ -I /path/to/eigen/ my_program.cpp -o my_program
> >
> >
> > How about also suggesting an example with typical release compile
> > flags? Something like:
> >
> > g++ -I /path/to/eigen/ my_program.cpp -o my_program -O2 -DNDEBUG
> > -march=native -mtune=native
> >
> >
> > Not sure whether it would really save any beginner from unknowingly
> > benchmarking different linear algebra libraries in debug mode, but at
> > least we can try. (I just read such a benchmarking report, with Eigen
> > and PETSc as the libraries... As you can imagine, the C library had
> > some speed advantages over the C++ template library under those
> > circumstances.)
> >
> > Regards,
> > Thomas
> >
> >
> >
>
>
> --
>   Dr.-Ing. Christoph Hertzberg
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