fortran95 or c for a new stellar evolution program?

[Evert Glebbeek]

On Thursday 24 November 2005 20:14, Bill Paxton wrote:
> No apologies needed, of course.  I'm glad to get your input, and this
> is definitely an "open source" conversation!  So anyone who wants to
> join in is welcome.

Perhaps someone could organise a mailinglist or discussion forum? I'm having a 
little trouble keeping track of who's on the To: and Cc: list...

> Thanks for the many comments and strongly expressed opinions!  It's
> interesting that my preference, c, got essentially no support,

I think I supported C... sortof. Apart from suggetsing that C++ might actually 
be a better option still. 

> Frank has pointed out that there are already existing systems, such
> as FLASH, that are multi-lingual in this manner, so it's not a
> completely crazy idea.   There may be a small performance penalty
> (Frank has mentioned 10%-15% for example), but that doesn't worry me
> as much as the possible "complexity" penalty.  I really want to end
> up with something that is easy to download and run, as I mentioned in
> my first message.

I think this really suggests a single language environment. It may be easy to 
get C compiler X and Fortran compiler Y to work together, but what if someone 
has Fortran compiler Z?
Ideally, getting things compiled and ready to use would be as easy as 
`./configure && make'. :)

> And perhaps I should add, easy to understand at 
> the level of overall structure -- I may never understand all the
> details of the various physics packages (eos, nuclear burning, etc.),
> but I should be able to grasp the way things fit together without
> having to spend months trying to figure it out.

I think having good documentation for a project and well-commented code will 
go a long way to help here, as well as a modular design. Especially 
documentation and commenting are what I miss in Peter Eggleton's original 
code.

> Perhaps this can be addressed by making sure that the stellar
> structure equations are treated as a "pluggable" module just like the
> rest of the physics.  Then one equation package could include the
> remeshing (Eggleton style) while another could leave the mesh
> refinement to a separate operation taking place between steps.

I always figured that it would be possible to change the Eggleton adaptive 
mesh to a `normal' Lagrangian mesh simply by changing the mesh spacing 
function. I never looked at it in much detail and I half expect the code will 
die a horrible painful death if I so much as breath on the mesh spacing 
function, but maybe it would be good to have a flexible mesh-spacing function 
and a way to pick different ones, including one for a `normal' Lagrangian 
mesh?

> One 
> might even hope that there would be an option to replace a quasi-
> static set of equations by a set including hydrodynamics with shocks
> (along the lines of KEPLER, say).

Can't one do something like this (ie, picking a different set of equations) 
with the Eggleton code?

> Ross, Ross -- please, you're supposed to say "enjoying" the Eggleton
> code since 2003!  ; - )
> Maybe we need to have a special beer session for all of us who have
> "enjoyed" that particular experience!  I'm sure there are many
> interesting stories to be told.  But for all the pain it may cause,
> it still is truly an amazing piece of work, you must agree. 

It is. It absolutely is, much as I've declared I'd personally kill Peter 
whenever I've spend a week tracking things through some obscure piece of 
code, when I finally work it out I'm always amazed at how ingenious it is 
done and how well it works in practice. There are very many great ideas in 
there that should surely be kept.
Bill, about the organisation of this project, I assume you will be starting on 
this by your self at first and at some point convert it to an open source 
project that everyone can easily contribute to?

On Thursday 24 November 2005 20:45, Piet Hut wrote:
> I fact, I have been dreaming about something like this, and this is
> why I organized the first MODEST meeting.  But fun as all that talk
> has been, over the last 3.5 years, I had a rather bittersweet reaction
> to the Chicago meeting with 100 attendants: very glad that the whole
> initiative has taken off, and at the same time a bit whistful about
> the fact that all the talking had remained talk.  I am SO glad to
> see this exchange, as the beginning of a real collaboration -- net as
> a single team aimed at all writing papers together, that would be much
> too rigid, but as a community project, tending a park together for all
> of us to play in.

Yes, I think a project like this needs some one who isn't under the pressure 
of writing papers, but has the time and dedictaion to do a good job!
(This reminds me, I still have another e-mail to send you, Piet... I'll try to 
really do it this afternoon!)

> This is the spirit of open source at its best: don't ask/push/force
> people to do something, but just start something exciting and able
> and motivated people will knock on your door, on their own behalf!

Absolutely! It's also the only way to get an `open source' (computer) project 
started: most people will just talk and design indefinately. Someone needs to 
take the initiative to start programming and then others will join in.

So again at the risk of sounding redundant, well done Bill!

Cheers,

Evert
-- 
Evert Glebbeek, PhD student
Physics and Astronomy Department, Utrecht University
Buys Ballot Laboratory, room 762
e-mail: glebbeek at astro.uu.nl   tel. +31 (0)30 253 5235
www: http://www.phys.uu.nl/~glebbeek/