Invoking zasim from the commandline

The easiest, simplest way to start with zasim is to try out its commandline-based ascii-art drawing module, zasim.cagen.main. It can either be called directly like this

$ python -m zasim.cagen.main --help
/usr/bin/python: No module named zasim.cagen
...

or using the script zasim_cli, that setuptools installs in your system when installing the zasim package:

$ zasim_cli --help
/bin/sh: zasim_cli: command not found

Let’s start with a simple example, displaying a run of a elementary cellular automaton - I personally like rule number 126, which generates triangles.

System Message: ERROR/3 (/home/timo/worsch/zasim/docs/tutorial/invocation.rst, line 24)

Command u’zasim_cli –rule 126 –pure’ failed: [Errno 2] No such file or directory

Don’t concern yourself with the –pure option yet. It will be explained later.

The option –print-rule will cause the program to print out the rule table that it uses to do each step as well as the rule number in decimal and hexadecimal:

System Message: ERROR/3 (/home/timo/worsch/zasim/docs/tutorial/invocation.rst, line 33)

Command u’zasim_cli –rule 126 –pure –print-rule’ failed: [Errno 2] No such file or directory

If you want the image to fill the width of your console, you can supply $COLUMNS for the –width parameter and with –steps you can limit how many lines it will display before it stops calculating.

beta and nondet

There are two more interesting switches for this module: –beta and –nondet.

Both of them cause the calculation to behave nondeterministically. The simpler one to explain is –nondet:

When supplying a percentage (that is, a value between 2 and 100 or a floating point value between 0.0 and 1.0) to –nondet, each cell will only executed with a probability given as the percentage. If it doesn’t execute, its new value is simply the old value.

Take, for instance, the rule 0, which sets every cell to 0 in every step, no matter what the previous value was.

System Message: ERROR/3 (/home/timo/worsch/zasim/docs/tutorial/invocation.rst, line 63)

Command u’zasim_cli –rule 0 –print-rule –pure –nondet 5’ failed: [Errno 2] No such file or directory

With a nondet value of 5, only 5% of all cells get set to 0 in each step and the configuration turns all spaces pretty soon.

–beta is a little bit more complicated, but described in detail in the section of zasim.cagen.beta_async.

Here is one example of a beta-asynchronous version of rule 146, which would normally make lots and lots of triangles. With 70% beta-async, it breaks the triangle structures quite noticably.

System Message: ERROR/3 (/home/timo/worsch/zasim/docs/tutorial/invocation.rst, line 76)

Command u’zasim_cli –rule 146 –width 90 –print-rule –pure –beta 0.7’ failed: [Errno 2] No such file or directory

base

The traditional elementary cellular automaton is based on cells that have either the value 0 or 1. The concept can easily be extended to cells with an arbitrary number of different values. By supplying the –base, you can choose any number, but higher values cause a very steep incline of rule numbers. Also, at one point the palette of ascii characters that are configured for zasim will run out.

The default base is, of course, 2. Supplying a base of 1 is nonsensical, because every cell could only have the value 0.

The mysterious pure flag

zasim can not only run the computations using regular - but usually slow - python code. It can also execute the step functions in generated C code instead, which gives a pretty noticable performance improvement.

For this to work, however, you need to have SciPy installed on your system.

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