Gun show (part 3)

Next (in reverse chronological order, but it makes sense to me) the p58 gun. I think “AbhpzTa”‘s version is pretty much the same thing as “Thunk”‘s (based on Matthias’s component), but in such a compact form it’s harder to see what’s going on. Here’s “Thunk”‘s:p58What we have here is not one but two herschel loops, both period 58. The top one is connected to the bottom one by another herschel track, and there’s a reaction that duplicates the herschels in the top track, sending one on its way around the loop again and another down toward the bottom track. But this doesn’t happen without input: it needs a period 58 glider stream. Where does it get one? Patience…

Where the cross track feeds into the bottom loop, the two herschels collide and out of the collision come not one but two gliders every 58 generations, heading southeast. They’re pretty close together. Too close, in fact, because we want to reflect one stream 90°, and that can’t be done without messing up, and getting messed up by, the other stream. So we use this cute reaction:

Screen Shot 2016-04-15 at 8.05.24 PMTwo perpendicular glider streams go in, two go out. Same directions, but displaced. Meanwhile the parallel glider stream just squeaks by. That puts the two streams further apart, but not by enough, so we do the same thing again. Now they’re separated by enough.

(But wait, that reaction needs a second glider stream, going northeast, to work. Two of them to make it work twice. Where do we get two? Patience…)

One of the two not-so-close-together parallel streams gets kicked to the right, and the other to the left, with this apparatus. It’s called a snark, and it’s by far the smallest and fastest stable glider reflector known. Here you can see a glider coming in from the northwest and another on its way out to the northeast.

Screen Shot 2016-04-15 at 8.14.17 PMThe stream that gets kicked to the left gets kicked left again, using a different, larger, oscillatory object, I think in order to get the correct glider phase or position for the outgoing stream. It’s now heading northwest, back toward the herschel loops — in particular, toward the intersection of the upper loop with the downward connector. That’s right, it becomes the glider stream needed to make the herschel duplicator work.

The other stream gets kicked to the right three times — now it’s heading northeast, crossing perpendicularly the two parallel streams, and it runs into a block at just the right time and phase to make the stream displacer work. Then it gets bent to the right four more times, putting it perpendicular to the two parallel streams again, so it can make the other stream displacer work. We didn’t need two new streams after all for the displacers, or even one… the displaced stream and both of the auxiliary streams are in fact all the same stream! Reminds me of a Heinlein story for some reason.

Finally, in the version “Thunk” posted, there’s one more kick to the right sending this stream off to the southeast to become the gun’s output, but there’s no need to do that; it could just continue to the northeast. And that’s the gun.Screen Shot 2016-04-15 at 8.43.32 PM

Unlike, say, the Gosper glider gun, which just needs two queen bees and two blocks to get started, this one relies on glider streams to work; it regenerates those streams itself, but it has to be built in the first place with glider steams to get started with. What happens, I wondered, if you erase one of the gliders heading into the herschel duplicator? Does it just create a gap in the output glider streams, or does something more serious occur? Something more serious, it turns out.



2 thoughts on “Gun show (part 3)

  1. The process of building this gun was probably one of the greatest-ever exercises in corollary sniping. Sokwe found all the important components, especially the kickback reaction that pushed the two glider streams apart where Snarks could reflect them. After that, it was a simple matter of connecting components and glider-stream piping–three streams in, four streams out. A purer example is the p59 gun in Golly’s patterns folder.

    One of the main complications was that there are two different orbits of glider color, and two orbits of glider phase (preserved because a p58 stream is even, but not divisible by 4). In redirecting the outer kickback stream into the reaction, I needed a reflector with different phase but the same color–the big p58 reflector thing was the closest I had at hand in jslife, as Elkies’ reflector and Kazyan’s bumper have different combinations of each. Abhpzta just used a different glider stream and an Elkies reflector to make that work.

    The other two connections needed the same color and phase–Snarks preserve both. Finally, I tried to minimize stream crossings because each one required debugging time, in scarce supply during the middle of a road trip (though this would not have been a problem anyway). Oh, and the extra snark is because that was required to prevent gliders destroying the gun in the original version posted. I simply forgot to delete it in the slightly-smaller version.

    Thanks to everyone that helped! And to doctroid for the writeup!

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