HartmutHolzwart wrote:Only slightly relates question: Is there a heurístic for guessing the number of gliders needed for a specific spaceship, e.g. depending on size, velocity and period? What are the major cost drivers (I sound like my budget controller ;-))?
Someone like Extrementhusiast or Kazyan would probably be better at answering this, so I'm just going to say a few random things and see if that provokes any disagreement from the experts.
How about "1-2 gliders per space dust cell"?
I do have one rule of thumb that
has actually worked (once) to produce a good advance estimate of number of gliders needed. It was based on the amount of "
space dust" in the target object -- about a 40-cell region, similar to the area taken up by a
25P3H1V0.1 or maybe an
Edge-repair spaceship 1. Based on glider recipes of these other known objects with about 40 cells of space dust, the estimate was 50-100 gliders, and the right number turned out to be 67.
Of course, that only works when objects with comparable size and structure are available
(and maybe not even then). I'm not sure how the rule could best be adjusted to account for the 264-glider synthesis of a
p6 pipsquirter, for example, which has less than 40 cells of space-dust rotor, but a big area of stator around it making the rotor less accessible. Probably it's safer to stick with spaceships for now, since they don't usually have a hard stable motionless crunchy outside and a squishy space-dust center.
Known Data Points...
30P4H2V0.4 has 70 or 80 cells of space dust, depending on how you count, but maybe it should get a discount for having a couple of B-heptominoes at the front. Its cost is 85 gliders -- seems reasonable.'
46P4H1V0 maybe also gets a discount for a pair of leading traffic light predecessors. It has about 50 space dust cells per half, 100 for the whole spaceship... and possibly an additional minor discount for symmetry. That one is 99 gliders, which also seems in line with a gradual increase in cost based on amount of space dust.
... But Not Enough to Extrapolate From
We really don't have enough data from these small spaceships to even make an educated guess about something the size of Sir Robin, which has something on the order of 600 cells of space dust. Even if the cost increase is roughly linear -- 1-2 gliders per space-dust cell -- we'd be looking at 1000+ gliders in a Sir Robin recipe. And I'm afraid the rule may be something more like "double the number of gliders every time you add 50 space-dust cells", which would give us a 100,000-glider estimate instead. (!)
Stable Stuff Is Good, Though
I think maybe we _can_ say that slower spaceships are significantly easier to construct. Or maybe the right thing to say is that spaceships with stable chunks are much cheaper, and stable chunks are much more likely as the speed goes down. The loafer's loaf, the copperhead's trailing block, and the central spine of
60P5H2V0 all make those respective synthesis problems a lot easier. Compare 60P5H2V0 with
44P5H2V0, a "
tough nut to crack" because there's nothing stable toward the middle to use as a starting point.
Period and velocity might not actually matter so much, except to the extent that higher period and slower speed help to enable stable centers.
Pretty much all the recent difficult syntheses have been done by finding stable objects or constellations that can be ignited by controlled explosions around the edges to make the target spaceship -- whether the final product actually has any stable stuff in it or not. That seems like a big hint for some specialized future version of lifesrc that searches for predecessors while maintaining an always-growing core of stability toward the center.
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