"glider loop" for single-glider-only oscillators, or no?

[dvgrn]

(This post was actually written on 2/15/2024, but Moderator Shenanigans(TM) were needed to get this post to the top of the thread. This explains the October date...)

Quoting part of a post from the "Reviewing Special:RecentChanges" thread, and moving several following posts to this new thread -- since the topic doesn't seem to be resolving itself immediately, and the extended discussion might get a bit more attention from the community here:

... confocaloid appears to have written one of the LifeWiki definitions (Loop) (EDIT: sorry, no, it's Loop (disambiguation)) that clearly implies that a glider loop can indeed consist of a glider bouncing back and forth. Any "back and forth" shuttle-like motion is going to prevent any possibility of multiple gliders in the loop, and yet that definition specifically mentions "back and forth".

I happen to think that confocaloid's definition in Loop (disambiguation) is correct, and that there's no need to try to exclude one-glider back-and-forth loops from any of the general LifeWiki definitions of "loop".

I'd personally prefer to see people use, e.g., "Jubjub shuttle" rather than "Jubjub loop" for oscillators consisting of two of the same reflector -- EDIT: especially if the glider is returning on the exact same lane -- because "shuttle" is more precise in that case, and it makes it more likely that people will know what a shuttle is due to having another good example to look at. But that doesn't mean that "Jubjub loop" is technically incorrect, or that anybody should be corrected for using it.

If this seems to be a controversial topic, it's probably time to create a new LifeWiki discussion thread for it.

[confocaloid]

In this case, confocaloid appears to have written one of the LifeWiki definitions (Loop) that clearly implies that a glider loop can indeed consist of a glider bouncing back and forth. Any "back and forth" shuttle-like motion is going to prevent any possibility of multiple gliders in the loop, and yet that definition specifically mentions "back and forth".
[...]

That is incorrect. I did not write any definitions in the linked page Loop.

What I did was to add "back and forth" to https://conwaylife.com/w/index.php?titl ... did=140460 which is another page. That was likely a copy/paste error due to the existence of Glider loop (a specific pattern, rather than a general concept). I don't know why nobody corrected that error.

It is incorrect to describe Jubjub reflector shuttles as "loops".

a p116 snark loop (not shuttle) can have 1 glider or more

That does not seem to be valid, either. Try to construct a p116 Snark loop with just one glider in it. Here is one with two -

Code: Select all

x = 51, y = 51, rule = B3/S23
20b2o$20bobo$22bo4b2o$18b4ob2o2bo2bo$18bo2bobobobob2o$21bobobobo$22b2o
bobo$26bo2$12b2o$13bo7b2o$13bobo5b2o$14b2o25bo$39b3o$38bo$38b2o3$33bo
12b2o$24b2o8bo12bo$3b2o19bo7b3o12bob2o$4bo20b3o11b2o4b3o2bo$2bo24bo11b
2o3bo3b2o$2b5o14b2o21b4o$7bo13bo8b2o15bo$4b3o12bobo7bobo12b3o$3bo15b2o
8bo13bo$3b4o21b2o14b5o$b2o3bo3b2o11bo24bo$o2b3o4b2o11b3o20bo$2obo12b3o
7bo19b2o$3bo12bo8b2o$3b2o12bo3$11b2o$12bo$9b3o$9bo25b2o$28b2o5bobo$28b
2o7bo$37b2o2$24bo$23bobob2o$23bobobobo$20b2obobobobo2bo$20bo2bo2b2ob4o
$22b2o4bo$28bobo$29b2o!

[...]
There are many forum posts containing incorrectly applied / inconsistent / misunderstood terminology. I'd say putting everything from the forums to the wiki unchanged is a horrible idea.
The forum posts will never be a consistent source for terminology (too many people using different wording, not always correctly, not always consistently).
However, the wiki can be consistent, and it should be consistent because the wiki is aimed towards readers/newcomers.

[dvgrn]

That is incorrect. I did not write any definitions in the linked page Loop.

What I did was to add "back and forth" to https://conwaylife.com/w/index.php?titl ... did=140460 which is another page. That was likely a copy/paste error due to the existence of Glider loop (a specific pattern, rather than a general concept). I don't know why nobody corrected that error.

It is incorrect to describe Jubjub reflector shuttles as "loops".

Right -- sorry, I did link to the wrong page. The Loop (disambiguation) page is the one I meant to link to, exactly as you have figured out.

Speaking for myself, I would never have been tempted to correct that "error", because it doesn't look like an error to me.

Glider loops are certainly allowed to have only one glider in them, and I don't see why any attempt should be made to exclude loops that that go back and forth, even when the "back" partially or completely overlaps the "forth".

A couple of posts up was my attempt at a survey of existing LifeWiki definitions. As they currently stand, the definitions that I found predominantly imply that "loop" can perfectly well apply to something like a Jubjub shuttle. Am I missing any other existing LifeWiki definitions that clearly state that "loop" should not be applied to back-and-forth gliders?

[confocaloid]

A couple of posts up was my attempt at a survey of existing LifeWiki definitions.

Once again, links "Loop" and "Glider loop" (in the post you linked) are incorrect. They should be links to disambiguation pages instead. EDIT by dvgrn: Fixed, thanks.

Further, I already wrote that the part "back and forth" in https://conwaylife.com/w/index.php?titl ... did=140460 is an error and should be removed.

Glider loops are certainly allowed to have only one glider in them, and I don't see why any attempt should be made to exclude loops that that go back and forth, even when the "back" partially or completely overlaps the "forth".

That's because "allowed to have only one glider" is different from "required to have only one glider".

An actual glider loop could have just one glider, but that is not a requirement. It is possible to insert a second glider (moving reflectors further away from each other if necessary), while still avoiding collisions. That would generally change period, but the mechanism remains the same.

In contrast, a shuttle made out of two 180-degree reflectors (with output glider lane on a collision path with the input glider lane) cannot be modified to have more than one glider, without gliders colliding with each other. Such shuttles are not loops. They don't look like loops, they don't feel like loops, and they don't function like loops either.

[dvgrn]

In contrast, a shuttle made out of two 180-degree reflectors (with output glider lane on a collision path with the input glider lane) cannot be modified to have more than one glider, without gliders colliding with each other. Such shuttles are not loops. They don't look like loops, they don't feel like loops, and they don't function like loops either.

It seems to me that that criterion for whether something is a loop or not, isn't quite the right criterion. For Jubjub shuttles specifically, where the glider bounces straight back and forth on exactly the same lane, the word "shuttle" does seem more appropriate to me. It's kind of an edge case -- a "zero width glider loop", which I'd rather call a shuttle but it could maybe count as a loop... at least, I don't think it's worth arguing with anybody who might want to put it in that category.

However, there are other cases where a glider loop cannot be modified to have more than one glider, without gliders colliding with each other -- and they're not shuttles. At best they're quasi-shuttles -- but "glider loop" seems like a perfectly accurate term.

I had the following as an edit to the previous post, but have moved it here:

EDIT: Here's an interesting sample usage of "glider loop" from way back in 1996:

From: Mark Niemiec
Date: Wed, 3 Jan 1996 11:14:23 -0800
Subject: New P15 glider-reflector


Just before Christmas, I found a new way of reflecting a glider 180 degrees
off a pentadecathlon and a P5 HW-sparker. There are two ways of doing
this (as in the two-pentadecathlon reflector), one of which has a
different phase than either the single- or double-pentadecathlon reflectors.
This permits construction of P105(+120n) and P165(+120n) loops.
This fills in all periods 15n except 45.

Code: Select all

#C P105 glider loop (extensible to 105+120n)
x = 43, y = 65
17b3o$16bo3bo$16bo3bo$17b3o5$17b3o$16bo3bo$16bo3bo$17b3o4$2bo4bo$2ob4ob
2o$2bo4bo7$31b2o6b2o$24bo4bo4bo2bo4bo$25bo3bo4bo2bo4bo$23b3o3bo4bo2bo4bo
$31b2o6b2o$21b2o2$19bo4bo2$14bo2bobob2obobo$14b4ob2o2b2ob3o$20b4o5bo$16b
2obo4bob2obo$16bo2bo4bo2bob2o$17bo3b2o2b2o4bo$14b3o2b3o2bobob3o$14bo2b4o
4bo2bo$15bobo2b2obobobo$16bo5b2obob2o$20b2obobo$20b4obo$24bo$20b2o$18bo
2bo$17bo2bo$14bo2b2obobo3b2o$14b3o3bobobo2bo$17b2o5b3o$16bo3b3o$16b3o4b
2o$14b2o3bob2o2bo$15bobo2bobobo$13bo2bob3obob2o$13b2obobobobo2bo$16bo6b
2o$16b4ob2o$22bo$16b6o$16bo$17b3o$19bo!

#C P165 glider loop (extensible to 165+120n)

Code: Select all

x = 58, y = 69
22b3o8b3o$21bo3bo6bo3bo$21bo3bo6bo3bo$22b3o8b3o5$22b3o8b3o$21bo3bo6bo3bo
$21bo3bo6bo3bo$22b3o8b3o3$28b2o$7bo4bo15b2o15bo4bo$5b2ob4ob2o28b2ob4ob2o
$7bo4bo32bo4bo11$2b2o6b2o16b2o16b2o6b2o$o4bo2bo4bo4bo9b2o9bo4bo4bo2bo4bo
$o4bo2bo4bo3bo22bo3bo4bo2bo4bo$o4bo2bo4bo3b3o18b3o3bo4bo2bo4bo$2b2o6b2o
34b2o6b2o$20b2o14b2o2$18bo4bo4b2o4bo4bo$28b2o$13bo2bobob2obobo6bobob2obo
bo$13b4ob2o2b2ob8ob2o2b2ob3o$19b4o12b4o5bo$15b2obo4bob2ob2ob2obo4bob2obo
$15bo2bo4bo2bob2obo2bo4bo2bob2o$16bo3b2o2b2o6bo3b2o2b2o4bo$13b3o2b3o2bob
ob5o2b3o2bobob3o$13bo2b4o4bo2bo4b4o4bo2bo$14bobo2b2obobobo3bobo2b2obobob
o$15bo5b2obob2o2b2o5b2obob2o$19b2obobo10b2obobo$19b4obo10b4obo$23bo15bo$
19b2o14b2o$17bo2bo12bo2bo$16bo2bo12bo2bo$13bo2b2obobo3b2o2bo2b2obobo3b2o
$13b3o3bobobo2bo2b3o3bobobo2bo$16b2o5b3o6b2o5b3o$15bo3b3o9bo3b3o$15b3o4b
2o7b3o4b2o$13b2o3bob2o2bo4b2o3bob2o2bo$14bobo2bobobo6bobo2bobobo$12bo2bo
b3obob2o3bo2bob3obob2o$12b2obobobobo2bo3b2obobobobo2bo$15bo6b2o7bo6b2o$
15b4ob2o9b4ob2o$21bo15bo$15b6o10b6o$15bo15bo$16b3o13b3o$18bo15bo!

Unlike the "Jubjub shuttle" case, I wouldn't really want to call either of these "shuttles". The second example is a pair of gliders that each travel in a figure-eight loop pattern.

The first example has just one glider -- you can't add two gliders to the loop, because the return path overlaps. And yet the glider isn't just going straight back and forth the way it does in a Jubjub shuttle. It's going around in a loop, so maybe "loop" is a better term than "shuttle" here.

[confocaloid]

Unlike the "Jubjub shuttle" case, I wouldn't really want to call either of these "shuttles".

I don't see anything resembling a loop in the second example. The movement of gliders is X-shaped.

In the first example, one could describe the movement of the glider as a (long and thin) "loop", but one couldn't add a second glider. The visual appearance disagrees with how the pattern works.

I think such examples illustrate the idea that common names can be misleading, without contradicting the general concept referred by the same words.
A specific pattern might happen to be commonly called 'p137 loop' or 'p137 glider loop' etc., without actually being a loop. That by itself does not contradict anything. It's just that names of patterns are not always consistent with terms for general concepts.

Names of patterns can be (and sometimes remain) misnomers. But general concepts should be meaningful, intuitive and consistent, as far as possible at all.

[dvgrn]

In the first example, one could describe the movement of the glider as a (long and thin) "loop", but one couldn't add a second glider. The visual appearance disagrees with how the pattern works.

Can you explain a little further about why, in that first example, you think that "how the pattern works" is not actually "the glider going around in a long and thin loop"?

I haven't been able to find any authoritative statement anywhere that says it's necessary to be able to fit two or more gliders into a loop, before it can be correctly called a loop. So at the moment I don't see why there's any actual inconsistency or disagreement involved with calling that first example a "glider loop".

[confocaloid]

In the first example, one could describe the movement of the glider as a (long and thin) "loop", but one couldn't add a second glider. The visual appearance disagrees with how the pattern works.

Can you explain a little further about why, in that first example, you think that "how the pattern works" is not actually "the glider going around in a long and thin loop"?

I think that is too relaxed to be useful.
An interesting common property shared by loops is that it's possible to change the number of gliders in the loop and change distances between reflectors. That results in different oscillators with periods that are a common multiple of periods of all involved reflectors.
In that example, the glider goes back and forth, but doesn't "go around" anything, and trying to put two or more gliders (that would ostensibly "go around" each other) fails.

Another non-example is those "dependent reflector loops". They're commonly called "loops", but they are not loops, as the period cannot be adjusted by moving reflectors and adding/removing gliders.

The book Conway's Game of Life: Mathematics and Construction says this in Chapter 3 (3.5 "Glider loops and reflectors"):

By using four carefully positioned reflectors, we can then create a track for a glider to follow, as we illustrate with buckaroos in Figure 3.27. That particular track takes a single glider 180 generations to traverse, and has two gliders on the track, resulting in an oscillator with period 90. By changing the number of gliders in the loop and moving the buckaroos farther away from each other, we can create an oscillator with any period that is a multiple of 30.
[...]
Furthermore, we can only place a single glider on the track in Figure 3.28, regardless of how far apart we space the pentadecathlons, since the input and output paths of the reflection overlap each other.

I think being able to change the number of gliders and rearrange reflectors is needed. If you can only put a single glider on a long thin back-and-forth track, it doesn't deserve to be classified as a loop.

Otherwise (playing for the other side), one might as well describe all oscillators (regardless of mechanism) as "loops", on the basis that they're looped in time; an oscillator loops through different phases (configurations of cells).
I don't think that would be useful, and I don't think it is useful to describe "single glider only" shuttles as loops.

[Haycat2009]

"glider loop" should be for single-glider-only oscillators and oscillators that allow multiple gliders.

"Shuttle" has periodic connotations, and should be used for loops where oscillators reflect gliders (by duoplet™, banana™ and the lot.)

On the other hand, snark, jubjub and galumpher loops are made of stable, independent reflectors. So loops should be used.

[confocaloid]

"glider loop" should be for single-glider-only oscillators and oscillators that allow multiple gliders.

"Shuttle" has periodic connotations, and should be used for loops where oscillators reflect gliders (by duoplet™, banana™ and the lot.)

On the other hand, snark, jubjub and galumpher loops are made of stable, independent reflectors. So loops should be used.

Every oscillator "has periodic connotations", pretty much by definition.
Changing periodic reflectors to stable reflectors (or vice versa) does not make a non-loop into a loop. If a Jubjub reflector is replaced by a periodic same-lane reflector (or if a pentadecathlon is replaced by a compatible stable 180-degree reflector), that does not change the degree of shuttleness of the oscillator. It is still a shuttle.

Describing an oscillator as a loop can only make sense, if the gliders moving in opposite directions can go "around" each other without colliding. Otherwise there is no loop in any particularly helpful sense, and it becomes misleading to apply the term.

[...]
In contrast, a shuttle made out of two 180-degree reflectors (with output glider lane on a collision path with the input glider lane) cannot be modified to have more than one glider, without gliders colliding with each other. Such shuttles are not loops. They don't look like loops, they don't feel like loops, and they don't function like loops either.

[Haycat2009]

Yes, but they travel in a loop-shaped configuration, so it is a loop. With additional reflectors, a jubjub loop can be made to have more than 1 glider, which supports the defination of "Confocaloid-loops".

[confocaloid]

Edit war in https://conwaylife.com/w/index.php?titl ... did=145706

Yes, but they travel in a loop-shaped configuration

There is no "loop-shaped configuration" where something would travel, either in the p118 or in the p142:

Code: Select all

x = 97, y = 40, rule = B3/S23
78b2o$79bo$78bo$78b2o11bo$16b2o58b2o11b3o$17bo57bo2b2o8bo$16bo59bobo9b
2o$16b2o11bo45b2obobo4bo7b2o$14b2o2bo8b3o49b2o3bobo6bo$13bo2bo9bo56bo
2bo4bobo$14bobo9b2o56b2o5b2o$13b2obobo12b2o$17b2o12bo$29bobo$23b2o4b2o
45bo$17bo5bobo37b2o9b3o$4b2o9b3o7bo34b2o2bo8bo19b2o$b2o2bo8bo8bobo33bo
2b2o3bo5b2o15b2o2bo$o2b2o3bo5b2o7b2o34bobo2b4o22b2obo$obo2b4o51bobo30b
obo$bobo27b2o29bob2o22b4o2bobo$3bob2o21b2o2bo28bo2b2o15b2o5bo3b2o2bo$
2bo2b2o21b2obo29b2o19bo8bo2b2o$2b2o27bobo45b3o9b2o$26b4o2bobo44bo$19b
2o5bo3b2o2bo35b2o$20bo8bo2b2o35b2o$17b3o9b2o39b2o$17bo45b2o$4b2o5b2o
49bobo$3bobo4bo2bo48bo13bo$3bo6bobo3b2o43b2o12bobob2o$2b2o7bo4bobob2o
44b2o7bobobo$7b2o9bobo46bo7b3o2bo$8bo8b2o2bo42b3o11b2o$5b3o11b2o43bo
11b2o$5bo11b2o58bo$18bo57bo$17bo58b2o$17b2o!

Yet, for some reason you are insisting that those oscillators should be classified as "loops", without any explanations why that would be either correct or useful or reasonable. In fact, labelling them "loops" is neither correct nor useful.

[dvgrn]

Edit war in https://conwaylife.com/w/index.php?titl ... did=145706

Yes, but they travel in a loop-shaped configuration

There is no "loop-shaped configuration" where something would travel, either in the p118 or in the p142...

I believe Haycat2009 is referring to a "loop" that looks something like this:

illustration of "loop" in Jubjub shuttle

degenerate-width-0-loop-in-Jubjub-shuttle.png (18.76 KiB) Viewed 817 times

Yet, for some reason you are insisting that those oscillators should be classified as "loops", without any explanations why that would be either correct or useful or reasonable.

Actually, I'm having a hard time seeing what I was thinking when I made that edit, and I don't at all mind that it was un-done. My edit summary shows that I was confused somehow: I was thinking that changing the color of 118 and 142 to purple would classify those two Jubjub shuttles as "glider shuttles" -- but no, the purple color is for "relay".

To make things even more complicated, I do actually think that a Jubjub shuttle might count as a relay. So I might want to change those colors back to purple -- but not right now! Maybe another color should be added instead, for the category "glider shuttle". Anyway, this discussion should happen first.

It's clear that, as the current definition of "relay" is written, most relays can correctly be described as loops, even though you definitely can't put more than one glider in the loop:

A relay is an oscillator in which spaceships (typically gliders) travel in a loop. The simplest example is the p60 glider shuttle...

"Relay" was defined way back in 1995 and was originally applied to things like the banks of relays in a primer pattern -- one glider per loop, overlapping paths in two opposite directions, 180-degree turn at each end -- but as far as I remember, until this discussion no objection has ever been raised about also calling them "loops".

The questions about what should happen with the two edge cases have never been addressed by the community, to my knowledge:

Edge case 1: Is a relay with a "degenerate width-0 loop" still a glider loop? (Obviously it's still a relay).
Edge case 2: Is a relay with four 90-degree turns rather than two 180-degree turns still a relay?

However, this is somewhat tangential to this thread's topic. I'll put in a separate post that's more in line with the main question.

[dvgrn]

In fact, labelling them "loops" is neither correct nor useful.

It seems to me that it's a little early to be stating this as a fact, in advance of some wider discussion in this thread.

Multiple people have found it useful to label these "degenerate width-0 loops" as loops. The LifeWiki's current definitions do not forbid this, as far as I've found so far, so it seems as if labeling them "loops" is also arguably correct as well as useful.

The only maybe-exception I've seen is the short glider loop oscillator definition, which currently reads:

"A glider loop oscillator is a closed track made out of several independent reflectors, with one or several gliders on the track. By changing the number of gliders and positioning the reflectors, it is possible to adjust the oscillator to infinitely many different periods."

That seems slightly imprecise to me -- you don't have to change the number of gliders, and technically you probably have to reposition the gliders as well as the reflectors. So, after this discussion, I'm currently planning to change the wording in that article to

"A glider loop oscillator is a closed track made out of several independent reflectors, with one or several gliders on the track. By changing the number of gliders and/or repositioning the gliders and reflectors, it is possible to adjust the oscillator to infinitely many different periods."

If this change is made, and if the "back and forth" wording in Loop (disambiguation) is not removed, then I think LifeWiki definitions will consistently imply that the narrowest glider loops are width 0, like the ones in Jubjub shuttles. That seems reasonable to me -- there doesn't seem to be any point in restricting the term "loop" to try to disallow only width 0, when there's evidence that people want to use the term that way.

"Loop" is a descriptive term, not a technical term, so it gets used in describing "things that look like loops", both on the forums and the LifeWiki. There's no technical definition of "loop" on the LifeWiki that excludes the degenerate case of "width-0 loops". It doesn't seem to me like any exclusionary technical definition needs to be added.

Comments, please? This is the thread for them!

[confocaloid]

Multiple people have found it useful to label these "degenerate width-0 loops" as loops. The LifeWiki's current definitions do not forbid this, as far as I've found so far, so it seems as if labeling them "loops" is also arguably correct as well as useful.

I disagree. It is not, in fact, useful to describe same-lane glider shuttles as "loops".
In a loop, the gliders have to go around some area. If there can be only one glider running back and forth (for example when gliders travel on the same path in both directions), then it is a shuttle, rather than a loop. It is a mis-use of terminology to describe the pattern as a "loop".

Also, I already posted a quote from the CGoLM&C book section 3.5, which also confirms and discusses the importance of being able to change the number of gliders in a glider loop and rearrange reflectors to adjust the period of the oscillator.

The book Conway's Game of Life: Mathematics and Construction says this in Chapter 3 (3.5 "Glider loops and reflectors"):

By using four carefully positioned reflectors, we can then create a track for a glider to follow, as we illustrate with buckaroos in Figure 3.27. That particular track takes a single glider 180 generations to traverse, and has two gliders on the track, resulting in an oscillator with period 90. By changing the number of gliders in the loop and moving the buckaroos farther away from each other, we can create an oscillator with any period that is a multiple of 30.
[...]
Furthermore, we can only place a single glider on the track in Figure 3.28, regardless of how far apart we space the pentadecathlons, since the input and output paths of the reflection overlap each other.

My edit summary shows that I was confused somehow: I was thinking that changing the color of 118 and 142 to purple would classify those two Jubjub shuttles as "glider shuttles" -- but no, the purple color is for "relay".

I think that is because of this edit, making things more confusing than they were: https://conwaylife.com/w/index.php?diff ... did=145691

Before edits by User:Haycat2009 ( https://conwaylife.com/w/index.php?diff ... did=145262 ), the page had zero mentions of relays. The changes were not previously discussed either.
I think the changes to the classification are destructive and should be reverted. They don't make sense as long as one is aiming for a sane, useful classification.

Revision before edits by the user: https://conwaylife.com/w/index.php?oldid=145262

[dvgrn]

I think that is because of this edit, making things more confusing than they were: https://conwaylife.com/w/index.php?diff ... did=145691

Aha, thank you! I was convinced that that edit must have been there, but somehow missed seeing it.

I'll roll back that change now -- it's clearly not the kind of thing that should get renamed without any discussion.

Also, I already posted a quote from the CGoLM&C book section 3.5, which also confirms and discusses the importance of being able to change the number of gliders in a glider loop and rearrange reflectors to adjust the period of the oscillator.

I read your quote when you first posted it, and went and looked at the book section you were quoting from. I couldn't find anywhere where it seems to say or imply that a loop should not be called a loop if it can only have one glider in it. It also doesn't say that single-glider-only shuttle-type loops _are_ loops -- it just doesn't seem to say anything at all about the question either way. So I don't yet understand why you've quoted and re-quoted those sentences.

The second part of your quote happens to call the track in Figure 3.28 a "track" rather than a "loop" -- but that doesn't imply to me that "loop" would not have been an equally correct and useful term to use there. Figure 3.27 also uses the word "track" even though it's clearly a loop. Some people might justifiably say that Figure 3.28 is also "clearly a loop": the glider can be seen as looping around the red dot, or the red line --

The center of the glider is first on one side of the line, then on the other side for the return half of the loop

Period-60-glider-loop.png (20.08 KiB) Viewed 766 times

[azulavoir]

Perhaps what we need is an expanded set of terminology... maybe we can say that any oscillator that bounces glider(s) around on more than one path is a loop (and if it's a 0hd 180-degree reflector pair, still a shuttle), and borrowing from the "infinite glider hotel" we can call loops that permit multiple gliders "hotels" as a whole?

[confocaloid]

I would not want to change existing terminology. Maybe what would work better is to add a new term (or several new terms) for those "generalized loops"? Something like 'loopoid', to describe something that is not a real loop, but can be viewed as a "generalized loop" in some sense.

Perhaps what we need is an expanded set of terminology... maybe we can say that any oscillator that bounces glider(s) around on more than one path is a loop (and if it's a 0hd 180-degree reflector pair, still a shuttle), and borrowing from the "infinite glider hotel" we can call loops that permit multiple gliders "hotels" as a whole?

If an oscillator consists of two 180-degree reflectors and a glider shuttling between them, with no possibility of adding more than one glider without having collisions, then that just means the oscillator can be correctly described as a shuttle. There is no need for any new terminology in this case.

For example, there are pentadecathlon shuttles, with two pentadecathlons and one glider. One cannot add a second glider without having collisions. Hence the pattern is indeed a shuttle, and there are no situations where one would need a different terminology.

If an oscillator is such that there can be (but is not necessary) more than one glider on the closed track without gliders colliding with each other, and reflectors also can be rearranged to get different periods, then it can be correctly described as a loop. Snark loops, bumper loops, bouncer loops, etc. are examples.

[dvgrn]

If an oscillator is such that there can be (but is not necessary) more than one glider on the closed track without gliders colliding with each other, and reflectors also can be rearranged to get different periods, then it can be correctly described as a loop.

Citation, please? It is still really unclear to me where you are getting this idea from.

It sounds like you're talking about adjustable glider loops, but then this tricky extra requirement (that it has to be possible to have two or more gliders in the loop) really surprises me -- it seems like it has come out of nowhere.

What exactly is wrong with simply leaving out the more-than-one-glider part of the requirement?

Then there'd be no need to invent "loopoids". The current word "loop" would seem to do a fine job of describing and labeling ... you know ... things that look like loops.

[confocaloid]

If an oscillator is such that there can be (but is not necessary) more than one glider on the closed track without gliders colliding with each other, and reflectors also can be rearranged to get different periods, then it can be correctly described as a loop.

Citation, please? It is still really unclear to me where you are getting this idea from.

I already referred to section 3.5 of the book. You replied to that that "it just doesn't seem to say anything at all about the question either way". However, the basic idea is discussed there. Loops can be adjusted to different periods by adding/removing circulating gliders / by moving reflectors. This is an interesting property, discussed when glider loops are introduced.

What exactly is wrong with simply leaving out the more-than-one-glider part of the requirement?

Then there'd be no need to invent "loopoids". The current word "loop" would seem to do a fine job of describing and labeling ... you know ... things that look like loops.

Neither pentadecathlon shuttles nor Jubjub reflector shuttles "look like loops".

A definition of 'loop' needs to exclude them. They are a different type of oscillators.

[dvgrn]

I already referred to section 3.5 of the book. You replied to that that "it just doesn't seem to say anything at all about the question either way".
However, the basic idea is discussed there. Loops can be adjusted to different periods by adding/removing circulating gliders / by moving reflectors. This is an interesting property, discussed when glider loops are introduced.

I agree completely with that entire quote. But discussing the basic idea does not mean that the book says "loops have to be able to contain more than one glider". It basically says that adjustable glider loops can be adjusted to different periods by adding/removing circulating gliders and/or by moving reflectors. You seem to be saying that it has to be an and and not an or, but there's no evidence in the book for that, and almost none in the LifeWiki either.

To be clear, here's a summary of our difference of opinion. You say

In a loop, the gliders have to go around some area. If there can be only one glider running back and forth (for example when gliders travel on the same path in both directions), then it is a shuttle, rather than a loop. It is a mis-use of terminology to describe the pattern as a "loop".

... and I would say something very similar, like this:

If there can be only one glider running back and forth (for example when gliders travel on the same path in both directions), then it is a shuttle as well as a loop. It is generally not a mis-use of terminology to describe a shuttle as a "loop" -- though it might be clearer to avoid the term "loop" for the degenerate "width-0" cases where the return lane is exactly the same as the outgoing lane.

[confocaloid]

Here is some oddity I guess, for people to have some more things to discuss.

The way it is written, it's basically a p2023 shuttloid oscillator --

Code: Select all

x = 254, y = 196, rule = B3/S23
76bo$75bobo$66b2o7bobo$66b2o6b2ob3o$59b2o19bo$59b2o13b2ob3o$39bo34b2ob
o$38bobo$36b3obo$35bo4bob2o48bo$35bobobobobo20bo26bobo$30b2o4b2obobo
21bobo20b2o3bobo$31bo8bobo5b2o13bo2bo19b2o2b2ob2o$31bobo7bo6b2o3b2o9b
2o$32b2o19b2o29b8ob2o$79b2o2bo4bo2bob2o$79bo2bo2bo$43b2o30b2o3bobob2o$
42bo2bo29b2o2b2obo5bo$43b2o37bo4bobo$82b2o2bo2bo$87b2o2$83bo$83b3o$35b
2o49bo22bo$35bobo10b2o35b2o21bobo$36b2o10bobob2o41b2o11b2obo$46bobob2o
bo7b2o31bo2bo13bo$34b4o3b2o3b2o14bo31bo2bo13bob2o$33bo2bo4b2o16b3o33b
2o10bobob2obo$33b2o3bo20bo47b2obo$37b2o71bo$110b2o4$21b2o$21bo$22bo$
21b2o$6b2o12bo$6b2o12b3o$23bo$22b2o$12bo$11bobo$3b2o6bobo$3bo2bo5bo10b
2o$4b2obo15b2o$b3o2bo$o3b2o101b2o$b2o22b2o80bobo$2bob2o14b2obo2bo75bo
6bo$2bo2bo13bobob2o78b2o4b2o$3b2o14b2o2bo78b2o$23bobo71b2o$7b2o15b2o
71b2o$8bo$5b3o$5bo3$45b2o$45bo3b2o$41b2o4bo2bo$36b2o3b2o3b4o$30bob2obo
bo$30b2obobo10b2o$34b2o10bobo$47b2o6$39b2o$38bo2bo$39b2o3$50b2o$34b2o
6bo7bobo$34b2o5bobo8bo$42bobob2o4b2o$40bobobobobo$40b2obo4bo$43bob3o$
43bobo$44bo74$223bo$223b3o8b2o$226bo7b2o$225b2o16b2o$242bobo3bo$242bo
4bobo$241b2o4bobo$246b2ob3o$252bo$246b2ob3o$246b2obo2$215b2o$216bo$
216bobo$217b2o2$252b2o$252b2o8$234b2o$234b2o4$231b2o$231b2o!
#C [[ THEME Catagolue ]]

I say 'shuttloid', because the two ends of the back-and-forth track have different 180-degree reflection mechanisms. The pattern has the Galumpher at one end, and it has a convoluted engineered same-lane 180-degree reflector at the other end. This allows it to have an odd period, unlike a proper shuttle.

Now, I believe that it happens to be possible to describe this particular shuttloid as a proper loop (and not just a loopoid). Even though the pattern has just a single glider running back and forth on a single long lane, it can be rearranged like this:

Code: Select all

x = 254, y = 190, rule = B3/S23
176bo$175bobo$166b2o7bobo$166b2o6b2ob3o$159b2o19bo$159b2o13b2ob3o$139b
o34b2obo$138bobo$136b3obo$135bo4bob2o48bo$135bobobobobo20bo26bobo$130b
2o4b2obobo21bobo20b2o3bobo$131bo8bobo5b2o13bo2bo19b2o2b2ob2o$131bobo7b
o6b2o3b2o9b2o$132b2o19b2o29b8ob2o$179b2o2bo4bo2bob2o$179bo2bo2bo$143b
2o30b2o3bobob2o$142bo2bo29b2o2b2obo5bo$143b2o37bo4bobo$182b2o2bo2bo$
187b2o2$183bo$183b3o$135b2o49bo22bo$135bobo10b2o35b2o21bobo$136b2o10bo
bob2o41b2o11b2obo$146bobob2obo7b2o31bo2bo13bo$134b4o3b2o3b2o14bo31bo2b
o13bob2o$133bo2bo4b2o16b3o33b2o10bobob2obo$133b2o3bo20bo47b2obo$137b2o
71bo$210b2o18$207b2o$207bobo$202bo6bo$203b2o4b2o$202b2o$197b2o$197b2o
6$223bo$223b3o8b2o$226bo7b2o$225b2o16b2o$242bobo3bo$242bo4bobo$241b2o
4bobo$246b2ob3o$252bo$246b2ob3o$246b2obo2$215b2o$216bo$216bobo$217b2o
2$252b2o$252b2o8$234b2o$234b2o4$231b2o$231b2o16$40bobo$40b2o$41bo24$
21b2o$21bo$22bo$21b2o$6b2o12bo$6b2o12b3o$23bo$22b2o$12bo$11bobo$3b2o6b
obo$3bo2bo5bo10b2o$4b2obo15b2o$b3o2bo$o3b2o$b2o22b2o$2bob2o14b2obo2bo$
2bo2bo13bobob2o$3b2o14b2o2bo$23bobo$7b2o15b2o$8bo$5b3o$5bo3$45b2o$45bo
3b2o$41b2o4bo2bo$36b2o3b2o3b4o$30bob2obobo$30b2obobo10b2o$34b2o10bobo$
47b2o6$39b2o$38bo2bo$39b2o3$50b2o$34b2o6bo7bobo$34b2o5bobo8bo$42bobob
2o4b2o$40bobobobobo$40b2obo4bo$43bob3o$43bobo$44bo!
#C [[ THEME Catagolue ]]

Note that I simply rearranged the reflectors around (two trombone slide adjustments cancelling each other) and added a second glider. The basic mechanism is still the same, but now there are two gliders running on a single closed track, without directly interacting with each other. The period is still 2023, but of course it can be adjusted as well by trombone slide adjustments and adding/removing gliders.

I think I would say that the reason why this particular shuttloid can be described as a loop is because one of two 180-degree same-lane reflectors was designed to have a loop inside it, and the back-and-forth segment of the track can be viewed as an internal part of an engineered 90-degree reflector consisting of a transparent-pond transparent-output-lane 90-degree reflector and the Galumpher, rather than a separate 180-degree same-lane reflector.

Any feedback on these contraptions is of course welcome (partly because most of my patterns are significantly smaller in size).

Returning back to the original question, I think in practice it would be better to keep the word 'loop' to refer only to things that actually look like loops, feel like loops, and can uncontroversially be classified as loops. At least as far as "what to say on LifeWiki" discussion goes.
Neither pentadecathlon shuttles nor Jubjub shuttles look or feel like loops to me.

Of course you cannot prescribe what people should say on the forums, as everyone will use a slightly different wording and different people have different preferences.
But that just means that occurrences in forum posts should not be semi-automatically transferred to the wiki. The wiki aims to be a resource primarily for interested readers and for newcomers. Cluttering the wiki with everything said on the forums would make it nearly useless.

[hotdogPi]

The only pattern that absolutely everyone can agree is a loop, with no controversy, is this.

Code: Select all

x = 5, y = 4, rule = B3/S23
b2o$o2bo$bobo$2ob2o!
[[ HEIGHT 300 ]]

[dvgrn]

Here is some oddity I guess, for people to have some more things to discuss.
...
Any feedback on these contraptions is of course welcome (partly because most of my patterns are significantly smaller in size).

Yup, I'd say those patterns are both shuttles and glider loops. The oddity seems like the kind of thing that often shows up with engineered patterns that are built to test the limits of a definition.

In this case, when you look at the pattern as a glider loop, the shuttle part of it has an adjustable but high repeat time. So the length of that 180-degree segment is often going to be the determining factor as to whether more gliders can be added to the loop, just because it makes the repeat time higher.

Never mind about "quasi-shuttle" ...
As a side note on possible names for shuttle-like things: on another thread Sokwe has pointed out that I was wrong about what "quasi-shuttle" is supposed to mean. It turns out that the LifeWiki article I was using as a reference has been wrong for the last half-decade or so. So I've patched up that article now.

Engineered patterns for "terminology testing"
There were some engineered patterns that I was thinking of building also, and come to think of it they're fairly easy to build. Here's a sample:

Code: Select all

#C p192 glider loop
x = 104, y = 104, rule = B3/S23
50b2o$50bobob2obo$52bobob2o$52b2o$43b2o$43b2o6$53b2o2b2o$50b2o5b2o$49b
o$52bo2$50b3o$40b2o13bo$40b2o8b3ob2o$44b3o7b2o$54bo3$54bo$54bo12b2o$
54bo9b2o2bo$45b2o17b2obo$41b2obobo20b2o$41bob2obobo14b3obo$47b2o14b3ob
o$62bo3b2obo$47b2o14b2o3b2o$47b2o16b2o$65bob3o$30b2ob2o34bo$24b2obo3bo
bo12bo$24bob5o2bo11bobo$30bobo13bo$25b2ob2o2b2o9b3o$25b2ob2obo11bo$28b
2obo53b2o$30bo44b2o8b2o7bo$76bo17bo$64b2o9bo17b2o3b2o$65bo9b2o9bo11b2o
$11b2o52bobo9bo7b3o6bo$b2o8b2o53bobo6b3o6b2obo6bo$2bo64bo3b2obo8b2o$bo
69b2ob2o8b2obo$b2o9bo5b2o3b3o14bo44b3o$3bo7b3o25bo46bo15b2o$b3o6b2obo
25b3o61bo$o8b2o26bo55bo6b3o$2o8b2obo24bo54bo6bo$11b3o65bo13bo7b2o$12bo
15b2ob2o2bo42bobo21bo$29bob2o2bo43bo21bo$19bo6b3o6bobo53b2o8b2o$19bo6b
o9bobo52b2o$4b2o13bo7b2o9bo$4b2o22bo9b2o$27bo$17b2o8b2o44bo$17b2o53bob
2o$60bo11bob2ob2o$58b3o9b2o2b2ob2o$57bo13bobo$56bobo11bo2b5obo$57bo12b
obo3bob2o$34bo34b2ob2o$34b3obo$37b2o16b2o$34b2o3b2o14b2o$34bob2o3bo$
36bob3o14b2o$36bob3o14bobob2obo$35b2o10b2o8bobob2o$36bob2o6b4o7b2o$35b
o2b2o5bo3b2o$35b2o9b2ob2o$47b2o2bo$49b3o$50bo2$46b3o$58b2o2b2o$55b2o5b
2o$54bo$57bo2$55b3o$45b2o13bo$45b2o8b3ob2o$49b3o7b2o$59bo4$59b2o$59b2o
$50b2o$46b2obobo$46bob2obobo$52b2o!

If a glider loop is built with unusually high-period reflectors, then technically only one glider can fit in the loop.

I'm thinking that this example is uncontroversial -- it's definitely a glider loop by anyone's definition -- because

A) there's no "back and forth" going on here (unless two 90-degree reflectors get artificially classified as a 180-degree reflector, at least!) and
B) it is definitely possible to adjust the loop to fit more gliders in -- it's only at this particular size that the loop is limited to one glider.

How about this case, though?

Code: Select all

#C p720 glider loop
x = 246, y = 246, rule = LifeHistory
102.2A11.A$102.2A10.A.A$114.A.A2.2A3.A$113.2A.2A2.A2.A.A12.A$117.A.A
3.A.A10.3A$113.2A.A2.4A.A10.A$113.2A.A.A3.A12.2A$117.A.A3.A$118.A.A3.
A30.2A$109.3A.A5.A3.2A30.2A5.2A$108.A.4A48.2A$107.A$108.2A$160.2A$
160.2A$73.A.2A9.2A.A5.2A69.2A$73.2A.A2.2A.2A2.A.2A4.A2.A68.2A$76.A.A.
A.A.A.A6.A.2A$73.3A.A7.A.3A3.A$73.A2.A.A5.A.A2.A2.2A$76.4A3.4A20.2A$
75.A3.A3.A3.A19.A$76.2A7.2A21.3A24.2A$110.A11.2A11.2A$75.4A5.4A35.A$
74.A.2A2.3A2.2A.A31.3A$75.2A.7A.2A32.A$148.2A.2A$146.A2.A.A.A$81.A.A
62.2A.A2.A$129.2A18.A$80.A3.A43.A.A18.2A$80.A3.A44.A17.2A2.A.A$81.3A
62.A2.A2.2A$147.2A2$77.2A$77.A.A7.3A$78.3A6.A.A$79.2A7.A82.2A$76.2A
10.2A37.A43.2A$76.3A9.3A35.A.A16.2A$89.2A35.A.A16.2A$127.A$77.2A87.2A
$77.2A18.A68.2A$97.A72.2A54.2A.2A$96.A.A71.2A48.2A3.A.A.A$90.2A5.A
121.A.5A.A2.A$89.A2.A4.A11.2A5.2A86.2A14.A.2A.2A.3A$82.2A5.A.A5.A13.A
3.A.A46.2A34.4A4.2A10.A.A4.A$82.2A5.A7.A11.2A5.A47.2A34.3A.2A2.2A8.3A
4.A.2A$96.A.A106.A12.3A4.2A2.A$90.A6.A22.3A94.2A6.5A$88.A2.A5.A22.3A
91.2A.3A$88.A.A21.3A6.A72.2A17.3A.2A6.5A$89.A23.A7.A72.2A18.2A2.3A4.
2A2.A$113.2A6.A96.3A4.A.2A$92.A13.2A4.2A6.A.A88.A8.A.A4.A$91.A.A12.2A
4.A.A97.A7.A.2A.2A.3A$92.2A18.3A95.3A6.A.5A.A2.A$111.2A.A5.A.A71.2A
24.2A3.A.A.A$112.3A6.A73.A2.2A26.2A.2A$112.2A7.A10.A.A60.2A.3A$101.2A
9.2A7.A9.A54.A9.2A.2A$100.A2.A9.A.A4.3A8.A3.A49.A.A10.A27.A$100.A11.
3A5.3A8.A53.2A39.3A$100.A11.3A16.A2.A94.A$100.A.2A27.3A94.A.A$102.2A
86.A2.A4.A2.A26.A.A$112.2A37.2A.2A32.3A2.6A2.3A25.A$111.3A38.A.A6.A
28.A2.A4.A2.A$101.2A9.2A37.A2.A.2A.2A.A15.A.A$101.2A48.3A2.A.A3.A14.A
$106.A65.2A2.A4.A$106.A46.2A4.2A.A9.2A.A2.A.2A62.2A$105.A.A44.A.4A4.
2A12.2A66.2A$152.2A9.A$160.A2.A2.3A$152.2A9.A2.A.A17.2A$105.A46.A.4A
4.2A2.3A17.2A36.2A$153.2A4.2A.A60.A.A$102.A5.A9.A104.A$99.2A4.A4.2A7.
2A30.3A2.A.A3.A59.2A7.2A$98.A.2A.2A.2A.2A.A5.2A31.A2.A.2A.2A.A68.2A$
98.A13.A39.A.A6.A22.4A$101.A7.A41.2A.2A27.2A54.2A.A$98.A2.A7.A2.A69.A
3.A3.A48.2A.3A$101.A.A3.A.A32.2A39.A6.A4.A49.A$98.A.3A.A.A.3A.A29.2A
39.2A9.A.A42.2A.3A$97.A15.A81.2A41.A2.2A$97.3A2.A.A.A.A2.3A123.A.A$
100.A.A.A.A.A.A70.2A6.2A45.A.A.2A.A$97.2A.A2.2A.2A2.A.2A66.A2.A4.A2.A
27.2A16.A2.A.2A$97.A.2A9.2A.A66.A2.A4.A2.A28.A19.A$180.A2.A4.A2.A28.A
.A16.2A$181.2A6.2A30.2A13.A.A2.2A$236.2A2.A2.A$241.2A2$39.2A$39.2A5.
2A166.A$39.2A5.2A67.2A96.A.A$38.3A74.2A97.2A$37.A2.A$15.2A19.A3.A5.A$
15.2A15.4A9.A.A87.4B$32.4A.A6.2A.2A.2A82.6B$36.A7.A5.2A81.7B82.2A15.
2A$9.2A33.2A86.4BD3B82.2A15.A.A$9.2A120.4BD4B101.A$13.2A26.2A87.4BD4B
102.2A$13.2A25.A2.A85.4BD4B$41.A.A84.4BD4B$43.2A82.4BD4B$44.A81.4BD4B
21.2A$8.2A30.2A83.4BD4B22.2A$8.2A30.2A82.4BD4B$40.2A81.4BD4B71.2A$28.
A3.2A7.A.2A77.4BD4B72.2A7.A3.2A$27.A.A3.A7.3A77.4BD4B81.A.A2.A$27.2A
3.A9.A77.4BD4B82.A.A4.A$31.A87.4BD4B84.A.5A$27.5A.A84.4BD4B87.A$27.A
4.A.A82.4BD4B77.A9.A3.2A$29.A2.A.A81.4BD4B77.3A7.A3.A.A$28.2A3.A7.2A
72.4BD4B77.2A.A7.2A3.A$41.2A71.4BD4B81.2A$113.4BD4B82.2A30.2A$88.2A
22.4BD4B83.2A30.2A$88.2A21.4BD4B81.A$110.4BD4B82.2A$109.4BD4B84.A.A$
108.3ABD4B85.A2.A25.2A$3.2A102.3BAD4B87.2A26.2A$4.A101.3BAD4B120.2A$
4.A.A15.2A82.3BD4B86.2A33.2A$5.2A15.2A82.7B81.2A5.A7.A$106.6B82.2A.2A
.2A6.A.4A$107.4B87.A.A9.4A15.2A$199.A5.A3.A19.2A$205.A2.A$30.2A97.2A
74.3A$30.A.A96.2A67.2A5.2A$31.A166.2A5.2A$205.2A2$3.2A$2.A2.A2.2A$3.
2A2.A.A13.2A30.2A6.2A$5.2A16.A.A28.A2.A4.A2.A$5.A19.A28.A2.A4.A2.A66.
A.2A9.2A.A$2.2A.A2.A16.2A27.A2.A4.A2.A66.2A.A2.2A.2A2.A.2A$2.A.2A.A.A
45.2A6.2A70.A.A.A.A.A.A$6.A.A123.3A2.A.A.A.A2.3A$3.2A2.A41.2A81.A15.A
$.3A.2A42.A.A9.2A39.2A29.A.3A.A.A.3A.A$A49.A4.A6.A39.2A32.A.A3.A.A$.
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This has got to be an unnecessarily convoluted example -- it's done this way just because I couldn't seem to find a duoplet-spark or banana-spark generator with enough clearance to turn a glider twice, quickly enough.

My idea would be that the central glider in the above pattern is going in a loop around the red line. The reflectors could theoretically support two gliders in the loop, but it doesn't work because the "back" and "forth" sides are too close together (though not overlapping).

It seems like it will be hard to find many people who would object to calling this a glider loop, even when the lanes are this close together. I'll be happy to be proved wrong about that, so if you're thinking "Silly dvgrn, that's not a glider loop" then please put in a quick post here to say so!

Until and unless posts like that show up, I'd rather not have the idea of "it must be possible to add multiple gliders or it's not a glider loop" find its way onto the LifeWiki.

[Haycat2009]

Yes. Jubjub loops can be adjusted, and both relay and shuttle have periodic connotations. Glider loop seems more correct for this. The lifewiki also said that this is correct.

Furthermore, if you exclude 180 degree loops, you must then exclude 90 degree loops as two 90 degree reflectors can make a 180 degree reflector.

Still, there is always the loop - so if the definition is changed, there will always be a loop. For eternity.