remove iterators and replace with for_each, parallel_for_each, parallel_reduction, ...

[SteffenSeckler]

Is your feature request related to a problem? Please describe.
Needed for proper kokkos support.
Also makes our lives easier

[SteffenSeckler]

particle deletion will probably become more complicated that way and probably needs an additional method, e.g., autopas::delete_if() or so.
This would also solve #435.

[SteffenSeckler]

or, probably also needed for the LC-reference-cell container (tentative name) just flag a particle as deleted and delete them only later.

[l-gaertner]

I will add a parallel_for_each in a future commit for #626
This will however just be calling the sequential for_each, until kokkos is integrated.

Additionally, examples (eg. md-flex) will be adapted in a future mr.

[FG-TUM]

I would actually like to use _parallel as a suffix in all of these names.

[l-gaertner]

I would actually like to use _parallel as a suffix in all of these names.

Camel cased or with underscore?

so forEachParallel or forEach_parallel ?

[FG-TUM]

Right, probably forEachParallel for consistency ;)

[l-gaertner]

On the topic of reductions:
Is there a necessity for "region reductions"?
Or are reductions currently (and in the future) always performed on all particles (still considering IteratorBehavior).

[FG-TUM]

Good question. I would assume reductions only of a subset of particles are also of interest.

[l-gaertner]

I know how to trigger your sense of creating Arbeitsbeschaffungsmaßnahmen and should probably stop right? xD

[l-gaertner]

Should we start to consider templating these?
Parallel and region forEaches and reducers [and const versions for both] start to generate a lot of code.
At least internally, for the public api this is probably a bad idea.

[FG-TUM]

I'd say just start implementing them, and when you notice that there is a huge overlap of code try to remove redundancies e.g. via templates or calls to helper functions.

[SteffenSeckler]

question: how are parallel foreachs named in kokkos or other codes? does it maybe make sense to use a similar naming scheme?

[l-gaertner]

question: how are parallel foreachs named in kokkos or other codes? does it maybe make sense to use a similar naming scheme?

parallel_for and parallel_reduce
https://github.com/kokkos/kokkos/wiki/ParallelDispatch

I would honestly keep it consistent with the rest of AutoPas.