I've noticed that there doesn't seem to be any established notation to refer to the 64 different Margolus rules (besides writing out all the transitions), so I've thought up a system of referring to them similar to the one for Wolfram cellular automata. I'd be surprised if no-one thought of a system like this before, but I don't see it in use anywhere, so...
Firstly, take the six transitions of the rule; for convenience, let's list them in the order David Eppstein's website does (each digit represents a 2x2 block):
Code: Select all
00 00 00 01 11 11
00 01 11 10 10 11
Eppstein's website writes "-> 1" if a live block is produced, and "-> 0" otherwise. For the Margolus rule simulated by 2x2 blocks in the 2x2 rule (B36/S125), which is the most well-known of the Margolus rules to the point of often being referred to as simply "the
Margolus rule", we have:
Now, we concatenate those six digits into one binary string, and convert that to a decimal number, like the Wolfram rule naming scheme does. Thus, the Margolus rule in B36/S125 can be referred to as Margolus Rule 8, or M8.
EDIT: I have decided to adopt dvgrn's suggestion below; the binary string is now converted to an octal number instead of decimal, meaning the Margolus rule in B36/S125 is now Margolus Rule 10, or M10.