CP/M/CPM_CDROM.iso/simtel/sigm/vols200/vol246/abstract.246

Text File | 1986-02-12 | 9KB | 214 lines

    The disk SIG/M 246, in addition to the usual ancillary files, is
entirely devoted to the library TORU.LBR. This is a specialized volume,
which requires familiarity with Conway's game of LIFE and some previous
knowledge of the programming language Convert.


        - - - -  T O R U . L B R  - - - -


    The motivation of the disk was to furnish an example of Convert
programming, but the example is interesting in its own right. We have a
typical example of programming in higher level languages, in which the
language is useful for quickly obtaining results, but whose code does not
deliver the speed and economy of which the CPU is capable. Convert can also
be used as a macro generator, to produce efficient machine language code.

    Once one has surmounted the novelty of learning the rules of LIFE
and working with some configurations which come readily to mind, it is
found that some systematic investigations have to be made. Both the folklore
and the few published results concerning LIFE show the results of following
the evolution of all the patterns built up from a few live cells - say up
to ten or twenty cells.

    Exploring all the configurations possible in a limited region is
one possible investigation, which quickly turns tedious because of the
exponentially large number of possibilities which have to be considered.
Here there are presented three programs,

        TOR4.COM
        TOR5.COM
        TORX4.COM

which examine all the states possible in tori of small dimensions - namely
4 and 5. Since TOR5.COM runs for a day and a half on a 5 MHz Intel 8085,
it is readily apparent that it will be hard to make an approach to a 6x6
torus, not to mention any larger ones.

    This brute force approach of working systematically through all the
possibilities may be somewhat questionable. When it is possible, it certainly
gives results in a straightforward manner. By analyzing the results which are
accessible in this form, it may be possible to formulate a more subtle approach
or even to refine the crude approach quite considerably.

    This refinement is already apparent in the programs here presented.
Rather than work on a complex macro assembler in Convert, results at first
were taken from the programs by executing them in HEX form with NDDT, using
either ^P or NDDT's disk output capabilities to obtain results.

    First, it was found that the program had to do its own writing to
disk, so that the results could be saved, edited, and reproduced. It was not
hard to extract this subroutine form another program and incorporate it into
the torus program.

    Next, it was found that there were too many repeated solutions,
because of symmetry. The torus not only has the eightfold symmetry of a
square (four rotations, with or without reflection) but the pattern can be
moved around on the torus. Forcing the center state to be a live cell is not
a very adequate solution to the problem. For the 4x4 torus, there are 128
symmerty variants of a given pattern; for a 5x5 torus there are 200 variants.
Not only does this produce a pile of paper, they all have to be sorted out.
So, the assembly language program produced by Convert was modified to reject
redundancies due to symmetry.

    Then, it is found that it is hard to keep a computer running for
long hours at a stretch. Power failures are an ever present threat, but
it also happens that other uses for the computer will be found, with a
certain impatience to interrupt the long program to get something else
done. Consequently an interrupt and restart procedure were called for.
At the same time it is nice to have the program give some reassurance
that it is still alive and how far it has progressed, when it is running
for long periods without actually producing output.

    Consequently, while one of these programs is running, one may
exercise one of the following options, by typing the corresponding key:

        =   Type the current state (console only) as a binary
            number to see how far the program has advanced.

        S   Close the output file TORn.DAT, then save a core
            image as RTORn.COM.

        ^C  Close the output file and exit.

As usual, ^C typed after ^S while console output is in progress will return
to CP/M, and the output file (at least its current extent) will be lost. To
restart a program that was saved, simply execute the saved core image. The
same program may be restarted several times in succession. Since each new
image uses the same output file, the previous TORn.DAT should be renamed
before restarting, supposing that its contents should be preserved.

    A word of caution - if TOR4.COM or TORX4.COM (TOR5.COM runs too
long to make its execution within TORU.HLP reasonable) is to be invoked
by HJELP from a menu, be sure that there is a little space on the disk to
hold the .DAT file (10K is sufficient), and that the disk is not write-
protected.

    As the results of a program begin to accumulate, additional ideas
begin to form as to what further results could be produced, what shortcuts
could be taken, and so on. Indeed, if the program is interesting at all it
will continue to evolve, and may end up with little resemblance to its
original form.

    For example, the results could be presented in a much more visual form,
without having to resort to pen and graph paper to truly appreciate them.

    The presence of TORX4.COM in the package is an example of this kind
of reasoning. Since the area that can be examined in a reasonable time is
limited to 25 or 30 cells, quite a few more possibilities in LIFE can be
sampled if they can be spread over different kinds of areas. Thus, some more
insight could be obtained by using a 4x5 rectangle in addition to the 4x4 and
5x5 squares. A rectangle can be closed up into a torus in several ways - by
giving it a slight twist for example. It could be made into a Moebius strip
or some other topological figure - all these variants imply a periodic pattern
in the ordinary plane which is used for LIFE. None of the variants replaces
analyzing an 8x8 torus; while the latter is beyond our reach, they will still
help in going beyond 4x4.


        - - - -  H J E L P . C O M  - - - -


    The entire library TORU.LBR is set up as both a SUBMIT file and as
a HELP file. TORU.SUB can be executed by typing

        RUN (TORU)

but is probably not too interesting to most people because its only function
is to use LU.COM to gather up TORU.LBR, which should NOT be on the disk prior
to execution.

    On the other hand, much of TORU.LBR can be browsed by typing

        HJELP (TORU)

and then working through the menus as in any other HELP file. HJELP has been
slightly modified for this disk, so that it maintains its own private I-O
area. This is necessary because of the new feature which has been added, that
.COM files can be incorporated in the menus and executed as part of HJELP. If
the file under execution also performs I-O to disk, it is essential that this
not clash with the I-O which HJELP will need to continue offering its menu and
passing to still further selections.

    It is still work for the future, to adapt embedded programs to the
format of HJELP. For instance, HJELP works best with 22 line panels, but this
is not the best format for a printed page. Thus if sample program output is
simply incorporated without revision into a HELP library, as is done in TORU,
its display will not be very aesthetic.

    Likewise, if a sample program produces copious output which runs off
the screen before it can be analyzed, its value is greatly diminished and the
reader is likely to be greatly annoyed.


        - - - -  A N C I . L B R  - - - -


    Since most SIG/M volumes contain a fixed set of ancillary programs,
we have decided to collect them into a library, so that they can be passed
as a group to a new disk which is under preparation. ANCI.LBR contains:

        USQ.COM        unsqueeze squeezed files
        REC.COM        recent version of REC80.COM
        CRC.COM        cyclic redundancy check
        LU.COM        pack and unpack libraries

    Two further ancillary programs,

        CNVSM.REC    Cnvrt compiler
        CNVLIB.REC    Cnvrt runtime library

are not included in the library because REC will not run programs from
the inside of a library, and to spare the user the inconvenience of having
to unpack them. Those LIFE enthusiasts who merely want to examine some LIFE
cycles will not need REC or Convert, but those who wish to see how Convert
is used to transform a protocol into an assembly language program may wish
to try out the process or to modify it.

    Finally, the programs

        RUN.COM        execute submit files & library programs
        HJELP.COM    browse through HELP files

were left outside of ANCI.LBR. RUN has to be, of course; HJELP gives the
most direct access to the main content of the disk and there is no need to
have to type RUN ((ANCI) HJELP) (TORU).

    For example:

        To run the cyclic redundancy check, type

            RUN  ((ANCI) CRC)

        To extract a library file, type

            RUN  ((ANCI) LU)

            and follow the normal instructions for LU.

        To unsqueeze FILE.EQT, type

            RUN  ((ANCI) USQ) FILE.EQT

        To see the main feature, type

            RUN (TORU)





[end]
[Harold V. Mcintosh, 9 August 1985]