Overview

Starform is an implementation of the Accrete algorithm. I've taken the code by
Chris Croughton and updated it according to my own criteria. I may not know 
much about the math, but I know a few things about programming, so my version
exists in search of the following goals:

 1. To have a good quality, documented, readable, comprehensible implementation
    of Accrete, useful for personal study, expansion, testing, embedding, and
    in general playing.

 2. To showcase a high-quality codebase that can be used to direct ports to 
    other languages as well as embed or call from other languages.
 
 3. To showcase modern C99 style and achieve an implementation that compiles
    without a lot of work under modern Unix operating systems, and Plan 9 (the
    supra-modern Unix).


In pursuit of these goals, my changes have mostly been as follows:

  - General refactoring, including renaming functions, breaking large functions
    into smaller ones, narrowing interfaces and interdependencies, and refining
    code responsibilities

  - Removing support for MS-DOS and other obscure/useless platforms I dislike.

  - Making the code more "objecty," removing global variables, doing less 
    up-front calculation in favor of lazier alternatives where possible.

  - Making starform into libstarform and changing the original utility into
    a shell that simply calls this library.


From here my goal is to produce a high-quality implementation of Starform in
several other languages. I'd like to start with Standard ML, because it can be
made to do things the C way if I must but is amenable to rewriting in a deeply
functional style. Eventually I'd like to finish ports to other languages, namely
Smalltalk, Common Lisp and Haskell, as at least one of these five languages will
certainly continue to exist in the next hundred years.

Finally, I intend to take the completed source code in all five languages and 
have six copies engraved in steel and launched into space in all directions.
Therefore, this code is licensed under the terms of the Revised BSD License.

Chris's README is below.

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Starform (also known as Accrete) was created by Matt Burdick in 1988.  Since
then it has been hacked about by many people.  This version is based on the
original released 'starform' code, as far as I know, with my hacks to it to
make it do what I want.

My changes are:

  Convert it to use ANSI C function prototypes, and have a header file for
  each module containing the exported functions and variables.

  Make it more modular, so that modules are not using data from modules that
  call them (and hopefully not calling functions 'upward' either).
  
  Put the 'main' function as the only thing in starform.c, so that (hopefully)
  all the other modules can be called by other programs.

  Add day/night and maximum/minimum temperatures for rocky (not gas giant)
  worlds.  The algorithm was stolen shamelessly from Stephen Kimmel's "World
  Builder" BASIC program, and then hacked about until it gave the sort of
  results my other simulations produce.

  Add stuff to list what materials are liquid on the planets' surface and
  what gasses might be in the atmosphere (if any).  It's guesswork to an
  extent (especially proportions), if you want to take it out look for
  function 'text_list_stuff' in module display.c and delete the calls to it.
  If you know more than I do about the amounts or properties (not hard!)
  please let me know any changes to make it better.  Note that I haven't yet
  made it look at the max and min temperatures to see whether stuff freezes or
  evaporates only part of the time...

  I've also added some ad-hoc moon generation stuff, if you define 'MOON' when
  compiling (add '-DMOON' to the CFLAGS variable in the makefile) then you'll
  get moons generated as well.  It's not scientifically based, though, so you
  probably don't want to do that...

Please read the INSTALL file to find out how to build it.

If you want to see the sort of output it produces, have a look at the EXAMPLE
files in this archive.

Chris Croughton, 1999.11.24
mailto:chris@keris.demon.co.uk

The following is Matt Burdick's original README file.

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This program is based on an article by Martyn Fogg in the Journal of the
British Interplanetary Society (JBIS) called 'Extrasolar Planetary Systems:
a Microcomputer Simulation'.  In it, he described how to generate various
sun-like solar systems randomly.  Since he did a good job of listing
references, I decided to implement it in Turbo Pascal on my PC.

Later, I translated it to C for portability, and the result is what you see
in front of you.  Because of my need to run this on an IBM-PC, there are two
makefiles included with the program: 'Makefile' (for unix systems), and 
'starform.mak' for MS-DOS systems.  To create the executable on a unix 
system, type in 'make' alone; type 'make starform.mak' if you are on 
an MS-DOS machine and using Microsoft C.

Thanks go to Sean Malloy (malloy@nprdc.arpa) for his help with the random
number routines and to Marty Shannon (mjs@mozart.att.com) for the
lisp-style output format, command-line flags, and various other pieces.

Enjoy, and if you find any glaring inconsistancies or interesting pieces to
add to the simulation, let me know and I'll include it in any other
distributions I send out.

Now for some references.  These are not the only good references on this 
subject; only the most interesting of many that were listed in Fogg's 
article in vol 38 of JBIS:

For a good description of the entire program:
	"Extra-Solar Planetary Systems: A Microcomputer Simulation"
	Martyn J. Fogg,  Journal of the British Interplanetary Society
	Vol 38, pp. 501 - 514, 1985

For the surface temperature/albedo iterative loop:
	"The Evolution of the Atmosphere of the Earth"
	Michael H. Hart, Icarus, Vol 33, pp. 23 - 39, 1978

For the determination of the radius of a terrestrial planet:
	"The Internal Constitution of the Planets"
	D. S. Kothari, Ph.D. , Mon. Not. Roy. Astr. Soc.
	Vol 96, pp. 833 - 843, 1936

For the planetary mass accretion algorithm:
	"Formation of Planetary Systems by Aggregation: A Computer Simulation"
	S. H. Dole, RAND paper no. P-4226, 1969

For the day length calculation:
	"Q in the Solar System"
	P. Goldreich and S. Soter, Icarus, Vol 5, pp. 375 - 389, 1966


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 I can be reached at the email address burdick%hpda@hplabs.hp.com
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