Tutorials/LLSSS

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This is a rough draft of a tutorial for basic LLSSS spaceship searches.

Lattice Life slice spaceship search (LLSSS) is a part of Keith Amling's rlife search suite available here. It is inspired by Andrew J. Wade's LSSS search program. Any questions about installing and using LLSSS can be asked in this forum thread.

Installing

Prerequisites

LLSSS is written in Rust and requires the Rust compiler. You can install the Rust compiler for your system by following the steps given here. This tutorial assumes that you are using a Unix-like command line terminal with git. Those running Windows may wish to compile and run LLSSS through Windows subsystem for Linux (WSL2). Compilation of LLSSS may take up to 7GB of RAM.

Downloading and compiling the program

First, create a new folder for LLSSS and open a command-line terminal in this folder. Clone the rlife repository with the following command: 

git clone https://codeberg.org/amling/rlife

Next, enter the newly created rlife folder by running 

cd rlife

To compile the program, run the following command: 

cargo build --release

Compilation will take several minutes and may take up to 7GB of RAM. Have patience.

When compilation is complete, the program binary will be contained in the newly created folder target/release. To enter this folder, run 

cd target/release

You are now ready to run LLSSS. When running LLSSS in the future, you can simply open a command terminal in the release folder without needing to recompile the program.

rlife actually contains three variants of LLSSS, called "llsss", "llsss-recentering", and "llsss-recentering-wao". Each works slightly differently, and requires slightly different input. For this example, we will find the turtle using a front-to-back search with even symmetry using each LLSSS variant.

First, we will set an environment variable that tells LLSSS to stop when it finds a solution. This is accomplished by running 

export LLSSS_HALT_ON_ENDS=true

If you wish to turn this feature off again, simply use the same command with "true" replaced by "false". If LLSSS_HALT_ON_ENDS is false, then many searches will run forever. If you want to kill the search while it's running, you can use the keyboard shortcut Ctrl+C.

llsss

To find the turtle using a fixed-width search, you can run the following command: 

./rlife llsss c3-f2b '@zero:9' --rule 'B3/S23' --left-edge even --filters wcaf > ouput.txt

Let's break down the input:

  • "./rlife" tells the terminal to run the rlife binary that we just compiled.
  • "llsss" tells rlife to run a fixed-width LLSSS search.
  • "c3-f2b" is the geometry of the search. In this case we're searching for c/3 orthogonal ships from front to back.
  • "'@zero:9'" is a "magic grid generator" for the geometry (see the options section for more details). In this case we are searching for a ship starting from empty ("zero") rows with "width" 9.
  • "--rule 'B3/S23'" sets the rule to Life.
  • "--left-edge even" sets the left edge to have even-width bilateral symmetry.
  • "--filters wcaf" is the "W-cycle avoidance filter". In this case, it stops the search if at some point all partial results have an empty first row (this would mean that no ships exist at the given width).
  • "> ouput.txt" sends the output to output.txt.

There are two things to note in particular about the above input. First, the "width" of the search is 9, but finding the turtle in an even-symmetric search should only require a width of 6. The extra 3 columns come from the fact that LLSSS includes both the duplicated column on the left (due to symmetry), and two empty columns on the right.

The other thing to note is that "--filters wcaf" isn't actually necessary for this search. In this example, the turtle will be found regardless of whether it's included. We include it here as a matter of good practice. If we did not include it, and a ship did not exist at this width, then the search would continue forever. To see this, you can try running the above search at width 8 with and without "--filters wcaf".

The above search will only take a few seconds to run. To locate the completed spaceship in the output, we need to search output.txt for the first occurrence of "[Info] End". In this case, you'll find something like this: 

[INFO] End ("LlsssEndsZero"):
[INFO] | ......... | ......... | ......... |
[INFO] | ......... | ......... | ......... |
[INFO] | ......... | **....... | **....... |
[INFO] | ***.*.... | ..*.**... | **.***... |
[INFO] | ***.**... | ....**... | ......*.. |
[INFO] | **....*.. | ...*.*... | ..**.*... |
[INFO] | ***...... | ..**..... | **....... |
[INFO] | ...**.... | **.**.... | **..*.... |
[INFO] | ...*..... | ..*...... | ***.*.... |
[INFO] | ..*.*.... | ....*.... | ...*..... |
[INFO] | ****..... | ....*.... | ......... |
[INFO] | ****..... | ......... | ***.*.... |
[INFO] | ....**... | *****.... | ******... |
[INFO] | ......... | ....**... | ***.**... |
[INFO] | .....*... | ......... | ......... |
[INFO] | **....... | ......... | ......... |
[INFO] | ......... | ......... | ......... |
[INFO] | ......... |           |           |

Notice that this shows just one of the symmetric halves of the turtle in each of its three phases. You will need to construct the complete symmetric spaceship yourself using a Life editing application, such as Golly or LifeViewer.

llsss-recentering

llsss-recentering is a variant of LLSSS that allows the center of the search to drift to the left or right analogously to floating rows in ikpx. The input is almost identical to that for llsss: 

./rlife llsss-recentering c3-f2b '@zero' 6 --rule 'B3/S23' --left-edge even --filters wcaf

Besides replacing "llsss" with "llsss-recentering", the only other difference is replacing "'@zero:9'" with "'@zero' 6". The new parameter after '@zero' is called the mid_steps and can be thought of as the "width" of a recentering search. In this case, a mid_steps value of 6 is sufficient to find the turtle.

llsss-recentering-wao

llsss-recentering-wao is an alternate recentering variant of LLSSS that uses a different method (other than --filters wcaf) to force live cells in the first row. The input looks somewhat different from the previous two setups: 

./rlife llsss-recentering-wao c3-f2b '@zero' 6 --wao-left-pad 0 --wao-right-pad 0 --wao-idx ALL --rule 'B3/S23' --left-edge even --wao-left-edge-errors

First, notice that we removed "--filters wcaf", as it's no longer necessary. We also added several new options. Most importantly, the new option "--wao-left-edge-errors" must be included if you set the "--left-edge" to some form of symmetry. It should not be included in an asymmetric search. The options 

--wao-left-pad 0 --wao-right-pad 0 --wao-idx ALL

are not discussed here. We will simply be including them (with these same values) in all wao searches in this tutorial.

Options

A list of options can be generated by running 

./rlife <search-method> --help

where <search-method> is one of "llsss", "llsss-recentering", or "llsss-recentering-wao". Some, but not all, of these options are documented below:

This section is incomplete.

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