[Stellar-discuss] n processors

[Piet Hut]

Hi Bill, and All:

Greetings from Lund, Sweden, where we are in the middle of the MODEST-6a
workshop (see http://www.astro.lu.se/~melvyn/modest6a.html).

The most interesting new development, right on the first day of the
meeting, Monday, Dec. 12, was that we clearly and somewhat unexpectedly
reached a critical mass of people interested in real hands-on
experimentation on glueing together stellar dynamics, evolution and
hydro; topics we've been talking about for years, but it suddenly is
all going to happen now.  So we decided that we needed a mailing list.
The question is: shall we use the "stellar-discuss" list for this more
general goal, or should we have a second parallel list.  Personally,
I think there will be so much technical overlap (how DO you couple
Fortran and C, or X and Y, and how DO you do this and that), that most
people will want to be on both lists.  So I propose widening the use
of "stellar-discuss" -- and of course, detailed questions in a
particular field can be addressed in the subject line as such, so that
not everyone has to read everything.

Bill, since you started to get the ball rolling, is that okay with you,
to enlarge "stellar-discuss" to talk about modeling stellar evolution,
stellar dynamics, and stellar hydrodynamics, as well as the question
how to interface all three?

As background information, let me try to summarize that part of the
first day of the workshop that is relevant for our discussion.

In the morning, we heard two talks, by Ross Church from Cambridge, UK,
and by Evert Grebbeek from Utrecht, NL, both present here already on
this email list.

Ross reported running various 10,000-body systems with NBODY6,
starting with single stars, where each star had a life Eggleton code
attached to it.  He showed HR diagrams, and good agreement with the
BSE code of Jarrod Hurley etal.  He also included physical collisions
between stars, but in a very simple way: after the collisions he
replaced the merger remnant by a ZAMS model of the same mass, simply
because he had not had time to do something better.

Evert followed, by reporting that he was able to do now exactly what
Ross had not yet done, namely to construct starting models for merger
remnants, in a fully automated way.  Starting from Jamie Lombardi's
make-me-a-star code, he constructed a merger remnant with a realistic
stratification of temperature, density, entropy, chemical composition.
He then carefully interpolated from ZAMS models to the required actual
merger remnant model, and he demonstrated that he could indeed start
Eggleton's code from those new models, all fully automatically.

Given that their efforts were nicely complementary, it will be very
natural for Ross to include Evert's work as a module to add to the way
her runs his code.  Work by others from the workshop might be relevant
here as well: Houria Belkus mentioned that she has a program to provide
spectra for a population of stars, so she could take snapshots that are
output by Ross's code, and transform those in observational spectral
information; this is in the context of her work with Joris Van Bever,
also in developing stellar dynamics/evolution codes.

In addition, Jan Pflamm, a graduate student from Bonn, showed me a
little scripting language that he had written, similarly to what Ernie
Mamikonyan, graduate student with Steve McMillan, had started doing,
to orchestrate stellar dynamics runs, making initial conditions,
integrating systems in time, and then analyzing them.  He told me that
he was inspired by the talk I gave at the end of the Modest meeting in
Edinburgh last year, in which I stressed the need for a very modular
approach.  Right afterwards, over Christmas, he started writing his
own modular environment, and I was very impressed to see what he has
all set up in one year.  He even wrote an Aarseth-like code from
scratch, like Joris van Bever, in C, based on Aarseth's book.  All
quite amazing!  And like Steve to Ernie, also Jan's PhD advisor, Pavel
Kroupa, kept saying to me that this was not his idea and that he was
not sure whether this was the right thing to do for his student, but
that clearly Jan did not want to do anything else.  (Steve, do I
represent Pavel and you correctly ;>?)

Well, having heard all these eager young people, we now have a pool of
graduate students who are actually hands-on working on writing Modest
sofware for their thesis projects.

This is the first time, in the three and a half years since we started
with Modest-1, that we are clearly going beyond repeating the same
talking discussions, and we are now moving into hands-on-working
discussions.  I now really feel that Modest is fully working.  So I
immediately called for an extra one-hour discussion breakout group,
at 5 pm, after all the normal talks and discussions were finished.
I defined the new discussion group around the topic of a "Framework"
for sharing modules in simulations.  The same questions of interfaces
and data structures came up again, as in MODEST-1, but now with the
context that a number of young folks are actually fully ready to start
working on it together.

So we decided to start an email list, and to begin writing toy model
codes, to act as stubs, so that we can first interface the stubs with
each other, as dummies to do some very simple simulations, much along
the lines of what Jun and I wrote for the review paper of Modest-1,
and what we put on the Modest web at that time; see our web site
http://manybody.org/modest/modest_star.html .

In addition, we started talking about scripting languages to
orchestrate the dance of modules in a simulation.  Jan Pflamm is
thinking about rewriting his own little language plus parser,
switching to Python instead (today I will make a few "ahum"
remarks about having a quick look at Ruby, just to point out that
there are alternatives as well ;>, but of course any scripting
language will do, and it is up to the developer what to choose).
This will be a rich topic for email list conversations, with now
Jun and me and Ernie and Jan all starting to write scripts for
experimentation -- and presumably Peter Teuben is itching to do
something similar for Nemo as well.

Greetings from Sweden, where today is the day of Saint Lucia,
the Queen of Light, a big tradition here: this morning in our
hotel over breakfast, ten students caroled for us in a lovely
way, with the woman playing Lucia actually wearing life burning
candles in her hair!!!  --  all reminded me somehow of the
dangers and problems of trying to integrate life stellar evolution
in a star cluster simulation . . . . an auspicious day to start a
new collaboration  q(^_^)p .

Cheers,

Piet