Xlife(6) Xlife(6)
NAME
Xlife - Conway's Game of Life, for X
SYNTAX
xlife [-geometry string] [initial pattern file]
DESCRIPTION
brings up a single window in which the user may experiment
interactively with cellular automata. In its default mode, the
program helps the user play with John Horton Conway's `Life' game.
By default Xlife will run in a window taking up 4/5ths of your screen;
you can use your window manager's Zoom or Resize feature to make it
fill the whole screen. This window is a viewport on a universe which
is effectively unbounded (4.2 billion on a side).
The -geometry option sets the Xlife window size and position as per
usual for X applications.
COMMANDS
8 Move your view of the universe up.
2 Move your view of the universe down.
6 Move your view of the universe right.
4 Move your view of the universe left.
5 Center the universe on the screen (based on
average position of the cells).
. Center the universe view on the cursor (also
Button 2 in normal mode).
=,+ Zoom the view in, magnifying the area around the
mouse cursor.
- Zoom the view out.
g Toggle running the game.
o Step forward one generation.
S Save the universe to a file adding extension .l.
If there is currently a boxed pattern, only the
boxed pattern is saved.
l Load (actually add to) the universe from a file
with extention .l. This lets you overlay multiple
saved states to make for some interesting effects.
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Xlife(6) Xlife(6)
Loaded pattern is initially considered tentative,
and may be manipulated in various ways before
incorporating it into main pattern. (To indicate
this, it's surrounded by a bounding box.) Clear
the universe if you want to start from scratch.
Load assumes pattern is in last directory
accessed.
h (Hide) stop displaying after each generation, does
not iconify.
c Toggle showing of cell counts
? Help for xlife.
! Place random cells on the area of the universe on
the screen.
r Redraw the screen.
R Change the (2-state) rules in "stays alive
on"/"born on" format. The standard rules are 23/3
(alive on two or three neighbors, birth on three
neighbors for an empty cell). Alternatively,
enable a payoff matrix with the syntax
<float>$<float> as described in the PRISONER'S
DILEMMA section.
F Load n-state rules from a given file (see the N-
STATE SUPPORT section below).
N Change the file's internal name.
A Add comments.
V View comments.
C Clear the universe. If there is a boxed pattern,
clear that instead.
Q Quit
f Run at a fast speed (no delay)
m Run at a medium speed
s Run at a slow speed
p Toggle running display of mouse position.
Position is only for reference during a session,
and does not effect coordinates of saved points.
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Xlife(6) Xlife(6)
O Set current mouse position to be the origin of
displayed coordinates.
G Generate tentative loaded pattern for one or more
steps.
U Undo load of tentative pattern.
I Force tentative pattern to be incorporated into
main pattern (automatic with g, h, o, l, and W
commands).
W Write (and flush from memory) script of loaded
patterns into a file with '.' extension. When
loaded, this script corresponds the earliest
ancestor of current pattern that can be
reconstructed from loaded patterns (does not
included changes made with mouse). Origin of
written pattern is mouse position when 'W' is
typed.
D Discard current load script, including any
tentative pattern, but leave cell population
intact. (Helpful for using an old pattern as a
template to construct a load script).
BUTTON BINDINGS IN NORMAL MODE
1 Activate a cell at the cursor.
2 Erase any previous selection box. If you drag the
cursor with button 2 held down, then release it,
the rectangle between the press and release points
is boxed and made tentative (as though it had just
been loaded and not yet incorporated). The
tentative pattern can then be moved, flipped, and
rotated before re-incorporating it.
3 Delete a cell at the cursor.
BUTTON BINDINGS WITH TENTATIVE PATTERN LOADED
1 Move pattern to current position.
2 Flip pattern about its x-axis.
3 Rotate pattern clockwise about its origin.
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Xlife(6) Xlife(6)
LOAD FILE FORMAT
A .l image file is an ordinary text file consisting of lines
terminated by the newline character. It is interpreted as one or more
image sections separated by section lines beginning with '#'. Lines
led by `##' are considered comments and ignored.
Each image section is interpreted according to the format letter
following its section line #. The format letters are:
A -- Absolute. Each line is interpreted as an absolute (x,y)
coordinate pair.
R -- Relative. Each line is interpreted as a relative (x,y)
coordinate pair.
P -- Picture. Each line in the section is interpreted as a scan line
of a relative image. Each '*' character turns the corresponding bit
on. All other characters leave the corresponding bit off.
I -- Include. A #I line should have whitespace-separated fields after
the #I consisting of a pattern name and five optional integer
parameters (x, y offsets, rotation, flip, and delay as defined in
section on inclusion, below). The named pattern is loaded as if it had
been included in the image at this point with the given transformation
applied. The offsets, if present, displace the load point of the
pattern relative to the current mouse position. The include facility
is useful for assembling `sampler' collections of interesting
patterns, as well as maintaining structured representations of complex
patterns.
B and E -- Pattern blocks. Patterns enclosed by #B <name> and #E lines
are skipped when loading a whole file, but may be accessed by adding
:<name> to the file name. They are useful for bundling related
patterns into the same file. Access is by sequentially skipping lines
not in the block, so excessive numbers of blocks in the same file may
slow down the loading process. Pattern blocks may not be nested.
Relative image sections are normally drawn with 0,0 on the current
mouse position (coordinates may be negative). This may be changed by
including a pair of whitespace-separated integers after the format
character. If this is done, these will be interpreted as a pair of x
and y offsets, and the image section will be drawn with its upper left
corner displaced from the cursor position by those offsets. This
facility can be used to write image files that will load patterns
centered on the cursor.
A leading image section with no header line is treated as though it
had a `#A' header. Thus, version 1.00 image files will load properly.
N -- Name This line contains the internal name of the pattern (which
may differ from the XXX.l name of the file.
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O -- Owner This line contains information on the person who wrote the
file, it is written in the form: id "name"@machine date, for example.
#O jb7m "Jon C. R. Bennett"@sushi.andrew.cmu.edu Fri Jan 12 18:25:54
1990
C -- Comment Lines begining with "C" are comments that the user may
have automatically writen to the save file, and which may be viewed
from within Xlife.
U -- Use Format is #U followed by a filename. This directive is
ignored if Xlife is in 2-state mode. In N-state mode (see below), it
loads a rule-set file just as if the user had typed in the name. If
the named file is already loaded, it will not be reloaded.
More section formats may be added in the future.
PATTERN INCLUSION
The #I command, as described above, has the following format:
#I <pattern> <x> <y> <rotate> <flip> <delay>
Any prefix of fields that includes a pattern name is acceptable, with
the natural defalts (no delay, no flip, no rotate, no y or x offset).
In the above
<pattern> 20
is a pattern name (described below);
<x>,<y> 20
are integers representing horizontal and vertical offsets; and
<rotate> 20
is an integer that specifies the number of times the pattern is
rotated 90 degrees clockwise around the origin. Any rotation
value (positive or negative) is acceptable, as all are taken mod
4 (true mod, not "%").
<flip> 20
is a multiplier (1 or -1) for the y coordinate that specifies a
flip about the x-axis. Other integers are accepted and silently
mapped to 1.
<delay> 20
is an integer specifying the number of generations to perform
before loading the pattern (negative values have same effect as
0).
Note that all of the transformations applied to an included
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pattern are taken relative to the pattern that includes it.
Thus, loading an assemblage of included patterns works as one
would expect.
A pattern name takes one of the following three forms:
<file> include whole file <file> (like old format)
<file>:<name> include pattern block <name> in <file>
:<name> include pattern block <name> in current file
(Note that <file>: is not allowed.)
A file may also include literal or pattern blocks. A pattern block is
a pattern given in any acceptable format between a line containing "#B
<name>" and another line containing "#E". Pattern blocks are skipped
when including a whole file.
(Note that pattern blocks cannot be nested.)
N-STATE SUPPORT
Xlife includes support for automata with up to 8 states using the
(von-Neumann-style) 4-cell rotationally symmetric neighborhood; to
invoke it, load a rule-set file using the `F' command. Many
interesting automata including the Wireworld construct and the UCC
described in E. F. Codd's 1968 ACM monograph can be implemented by
specifying appropriate transition functions.
When Xlife is used in this mode, the program uses color to indicate
states. Pattern picture files may contain digits to specify the
states of picture cells; `*' is interpreted as 1. Color-picker radio
buttons are set up at the right-hand side of the input window; by
clicking your cursor on a button, you set button 1 to paint with that
color. You can return to 2-state mode with the `R' command.
Refer to the rule-set file `codd.r' for an example of transition
definition syntax. Each line contains either a directive or 6 digits
arranged as
<old-state><neighbor><neighbor><neighbor><neighbor><new-state>
For <old-state> or <neighbor> you may also specify a state set; digits
enclosed in square brackets. This wild-cards the transition in the
obvious way. Comments (begun with `#') are permitted in the file.
You can arrange for rulesets to be loaded automatically by putting a
`#U' directive in a pattern file. When you save a pattern, a #U is
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automatically generated into the save file giving the name of the
current ruleset.
The directive
states <maxstates>
tells the code what the automaton's count of cell states is. The
default is 8.
If, while evolving a pattern, the code finds a cell and neighborhood
in a state for which no transition has been specified, the program
queries the user for a new state, and the tuple implied is added to
the database. This behavior can be modified by including a line of the
form
passive <maxstate>
which instructs the code that all combinations of cell and neighbor
states up to and including <maxstate> for which there is no explicit
rule leave the cell status unchanged. A `passive' declaration in a
rules file can be partially overridden by later, explicit transition
rules.
You can also specify rules depending on a neighbor count. A rule line
of the form
S(N*C)R
with S, N, C, and R being digits, is interpreted to mean that if a
cell has state S and exactly C neighbors of state N, the result state
is R. For an example of usage, see the Wireworld rules file.
When the evolution function encounters a neighborhood for which there
is no defined transition, it stops and boxes that neighborhood. You
are prompted for a result state. Once you've entered it, the
evolution function continues and the new transition rule is appended
to a new-transitions file in the current directory.
PRISONER'S DILEMMA MODELS
In the June 1995 Scientific American, the article "The Arithmetic of
Mutual" Help" (by Martin A. Nowak, Robert M. May and Karl Sigmund)
describes an interesting class of cellular automata that model
iterated Prisoner's Dilemma situations. These games can illustrate
stable and winning cooperate/defect strategies for situations in which
each agent repeatedly interacts with near neighbors. In the same
issue, Alun L. Lloyd's "Mathematical Games" column goes into more
detail about these simulations.
These are two-state automata. In Alun's implementation one state
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Xlife(6) Xlife(6)
always cooperates, one always defects (higher states could model Tit-
for-Tat, Generous Tit-for-Tat, or Pavlov). There is a payoff matrix
of the following form:
center box tab(;); l | c c. Payoff;Cooperate;Defect _ Cooperate;1;a;
Defect;b;0
To make the game interesting, b must be greater than 1. (Lloyd's
simulation only considers the case a = 0.) On each round, each cell
first plays the game with each of its neighbors in turn. Then, each
cell looks at the payoffs of its neighbors (and its own payoff) and
switches to the strategy with the highest payoff).
To set up such a game, use the `R' command in the following form:
R<b>$<a>
For example, to set up Lloyd's simulation, do `R1.85$0'. In these
simulations, use the following mapping between states and strategies:
0
Quiescent.
1
Live, always cooperates.
2
Live, always defects.
Interesting b values are in the range (1, 2]; Lloyd likes 1.85.
Different values produce wide ranges of different behaviors, including
stable end states, statistical equilibria and cycles with large
swings. Initial clustering of cooperators is also important; a single
cooperator will always be snuffed by surrounding defectors, but a
block of 4 or more may be able to defend themselves and earn a high
enough relative payoff to convert neighbors.
Lloyd included illustrations of a 1.85 game starting with one defector
in a sea of cooperators. The resulting patterns look like Persian
carpets or Koch snowflake curves.
OTHER FEATURES OF RULE FILES AND
The directive
debug 1
will enable single-step debugging of pattern evolution (so you can
watch the transition function being applied). Diagnostic messages
will be sent to stderr.
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Xlife(6) Xlife(6)
Transition rules entered interactively are appended (commented with
user ID and timestamp) to the file new.transitions in the current
directory. This file can later be selectively merged with your
original ruleset using a text editor.
ENVIRONMENT
The program has a compiled-in default for its global pattern
directory, LIFEDIR, which is normally /usr/local/lib/xlife.
If the the variable LIFEPATH is set to a colon-separated list of
directories, these directories (and their first-level subdirectories)
will be searched for pattern-file names and rulesets. The default
list includes "." and LIFEDIR; that is, pattern files are searched
for, by default, below the current directory and below the global
pattern directory.
The recommended way to organize your pattern directories is to have
one subdirectory per automaton. The distribution provides the
following:
life
contains an extensive library of interesting Life patterns.
codd
contains transition rules and components for the universal computer-
constructor described in E.F Codd's Cellular Automata Academic Press
1968 (ACM Monograph #3).
wireworld
contains transition rules and a test pattern for the Wireworld
automaton as described in the January 1990 issue of Scientific
American (Computer Recreations, p. 146).
misc
contains patterns for miscellaneous other automata.
These will be copied under LIFEDIR by a normal installation.
EXPLORATION
Here are some 2-state rules to experiment with:
23/3 the default, of course; Conway's "Life" rules.
1234/3 patterns "crystallize"
12345/45 patterns become contained
12345/4 same as above, but settles VERY quickly
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Xlife(6) Xlife(6)
5/12 floor tile patterns... Variations of this tend to
be interesting as well.
/2 most patterns expand indefinitely, some
interesting ones. Fast gliders.
BUGS
Old files in #P format may not have same y coordinate when read by the
new release. For best results, use "lifeconv -p name ..." on old
files.
Expose events don't restore the tentative pattern.
AUTHORS
Algorithm, implementation and file format enhancements: Jon
Bennett <jcrb@cs.cmu.edu>
Original X code: Chuck Silvers <cs4n@andrew.cmu.edu>
Enhancements to #I format and user interface: Paul Callahan
<callahan@cs.jhu.edu>
Auto-sizing, load format enhancements, 8-state support, all of the
non-Life automata, still-life detection, boxing: Eric S. Raymond
<esr@snark.thyrsus.com>
SEE ALSO
lifesearch(1), lifeconv(1).
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