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

[Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx>]

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


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