The clock a share cannot see
Worth reading first: How long a stem takes to settle · A pattern with a rate · The angle is an output.
Settling was tested for from this collection’s first essays and timed only recently, and the number it came back with was reassuring: where a stem settles at all it does so within 290 organs, and most inside fifty, against the four hundred every ablation run grows before it cuts anything.
That number has been carried since as a property of the rule. It is a property of the exponent.
The measurement
A stem is settled from the first organ after which every later divergence is within a degree and a half of the run’s own final value, held for sixty organs, with mirror arrangements folded together first — a run ending on 220.9° has settled on the same arrangement as one ending on 139.1°.
The same test at four falloff exponents, eight rises, nine starting angles and twelve hundred organs a run. Two hundred and eighty-eight stems, of which 117 settle.
The numbers
At exponent 2 the slowest settling is 160 organs. At 3 it is 290. At 4 it is 808. At 5 it is 674.
The exponent-three figure is the published one, arriving again from a sweep that was not built to reproduce it — a check worth having, since a table with four columns and no anchor is a table nobody can place.
Between the shallower half of the sweep and the steeper half the slowest settling grows by a factor of 2.8.
Why a share could not see it
The share of starting angles that reach a lattice does not move with the exponent — 30, 31, 29 and 27 of 72, inside one another’s error bars.
A share is a count of runs that settled. A run that settles at organ 8 and a run that settles at organ 808 are the same entry in it. So the quantity that does move is invisible to the quantity that was measured, and the two are read off the same 288 runs.
That is the ordinary way for an effect to be missed: not by measuring badly, but by measuring a statistic that is constant on the thing that varies.
The distributions, not just the maxima
The slowest is one number out of each column and it is worth checking that it is not carrying the claim alone.
At exponent 2 the thirty settling times are 0, 0, 0, 11, 12, 13, 14, 15, 15, 15, 16, 19, 22, 23, 28, 36, 36, 42, 42, 48, 48, 48, 48, 52, 59, 66, 69, 108, 113, 149 and 160 — of which three are above 100 and none above 200.
At exponent 4 the twenty-nine are 0, 0, 8, 8, 8, 8, 8, 9, 10, 11, 13, 13, 13, 19, 20, 26, 35, 40, 44, 63, 102, 147, 148, 157, 254, 273, 276, 462 and 808 — of which nine are above 100 and five above 250.
So it is not one slow run. The steeper columns have a tail the shallower ones do not, and the maxima are the visible end of it.
Where the tail sits
At the fine rises. Every settling time above 250 organs anywhere in the sweep — nine of them — is at a rise of 0.005 or finer, and eight of the nine are at exponent 4 or 5. The ninth is the 290 at exponent 3 that the settling table already reported.
That is the corner of the table where the basin is closing — one to four of nine starting angles reach a lattice there at all — so the runs that do settle are the survivors of a nearly-closed basin, and they take a long time to arrive.
Which suggests the two effects are the same effect seen twice: as the basin narrows, the paths into it get longer. The share does not measure the length and the length does not measure the share.
It is still a wall
The obvious worry is that the steeper columns are simply slower, and that a run which failed at twelve hundred organs would succeed at more. At exponent 5 a 1,200-organ run is barely one and a half times the slowest settling in the column, which is not a comfortable margin.
So the budget question is asked again at every exponent, the same way it was asked at exponent three: every run near that exponent’s own wall grown to 1,200 organs and then to 3,200.
Seventy-two pairs, and none of them gains a settled stem at the longer length.
Which is a stronger statement than it was
At exponent three the result was that tripling the run length changes nothing, on runs whose slowest settling was 290 organs — so the shorter length was already four times the slowest arrival and the null was unsurprising.
At exponent 4 the slowest arrival is 808 organs, so 1,200 is one and a half times it and 3,200 is four times. The margin the exponent-three result had for free has to be bought here, and buying it gives the same answer.
So the wall survives the one parameter that was expected to move it, and it survives the objection that the steeper rules were merely being cut off early.
What “settled” means at 808 organs
Worth pausing on, because the test has a shape that could be gamed by a long enough run.
Settling is the first organ after which the divergence stays within a degree and a half of the run’s own final value, and a run whose tail wanders has no settled value to have arrived at — the tail’s own spread has to be under a degree and a half before any settling time is reported at all.
So a run reported as settling at 808 is a run whose last four hundred organs sit inside 1.5° and whose organ 807 does not. That is a genuine late arrival rather than a slow drift being called an arrival.
What it changes about the ablation runs
Every cut in this collection is made at organ 400 of a stem grown at exponent three, and the justification is that settling takes at most 290 organs — so the stem is on its lattice before anything is done to it.
That justification is exponent-three’s. At exponent 4 or 5 a cut at organ 400 would sometimes be a cut into a stem that has not settled, and the resulting measurement would be about the arrival rather than about the removal.
Nothing here cuts at those exponents, so nothing is wrong. What is now known is that the margin is not a property of the rule and would have to be re-measured before any ablation thread moved off the working exponent.
The general shape
A number measured once at a working parameter value and then carried as a property of the model.
This collection has a name for one version of that and it is not a rare mistake. What makes it worth writing down here is that the number was measured carefully — nine starting angles, a control, two run lengths, the mirror fold — and the care was all inside the one exponent.
A careful measurement at one parameter value is still a measurement at one parameter value, and nothing about the care says which of the two it is a property of.
The zeroes
Several runs settle at organ zero, and they are worth explaining rather than leaving in a list.
A settling time of zero means every divergence in the run, from the first, is within a degree and a half of the run’s own final value — the stem was on its lattice before it had grown. That happens when the starting angle is already the answer, which is why the golden angle is included among the nine as a control rather than as a measurement.
It also happens at coarse rises from other starting angles, because a coarse lattice has few arrangements to choose between and the rule finds one in the first few organs. Both kinds are in the lists above and neither carries the result: the claim is about the slow end of each distribution.
What the exponent does to the destinations
Something, and it is the third of the three readings: the steeper columns reach divergences the shallower ones never do.
That matters here because a slow arrival and an unusual destination could be the same phenomenon. A stem heading for 42.3° at exponent 5 is heading somewhere no exponent-2 run goes, and it takes hundreds of organs to get there.
The two are correlated in the table and the correlation is not tested. Every settling time above 250 organs is at a fine rise, and two of the three steep-only destinations are also at fine rises, so the two effects share a corner of the grid.
Why the two lengths are 1,200 and 3,200
Inherited rather than chosen. The settling thread grew every run at those two lengths, and using different ones here would have made the comparison between this table’s exponent-three column and that table a comparison of two designs.
The ratio is 2.67, which was generous when the slowest arrival was 290 organs and is adequate when it is 808. If a future sweep found a slowest arrival near 1,200, the shorter length would stop being a length at which anything can be said to have failed, and the pair would have to move.
Naming that now is cheaper than discovering it: the guard is that the shorter length should be at least twice the column’s own slowest arrival, and at exponent 4 it is 1.48 times.
What is not claimed about the times
That the exponent is the only thing that moves them. The rise moves them too, and more: every settling time above 250 organs anywhere in the sweep is at a rise of 0.005 or finer, at every exponent.
So the right statement is that the two act together. At coarse rises every column settles quickly, and the differences between exponents are a few organs. At fine rises the shallow columns still settle quickly and the steep ones do not, which is where the factor of 2.8 comes from.
An interaction of that shape is what would be expected if the exponent were making an already-difficult approach harder rather than making every approach harder. It is not tested as an interaction, because a sweep with nine runs a cell cannot support one.
Reading the four columns as one distribution
Pooled across all four exponents, 117 stems settle and their times run from 0 to 808 organs, with a median in the low twenties and a long right tail.
That is a heavily skewed distribution, which is why the maximum is the statistic being compared rather than the mean. A mean over a skewed set moves with the tail and hides the fact that most arrivals are fast; the maxima are 160, 290, 808 and 674, and the medians are all between 15 and 20.
Both belong in the description. Most stems settle almost immediately at every exponent, and the ones that do not take three times as long at the steeper ones.
Where the number had been used
Twice, and neither use is wrong.
It justified the run length every ablation grows before it cuts: four hundred organs against a slowest settling of 290, so the stem is on its lattice when the removal happens. And it settled the question the settling thread was built for — whether the fine end of the ladder is a budget or a wall — by showing that no run here needs the length it is given.
Both of those are exponent-three statements about exponent-three runs, so both stand. What changes is that the second of them now has a second establishment behind it: the same comparison at every exponent gives the same answer, including at the exponent where the margin is thin.
What a slow arrival looks like
Not a stem drifting. A run reported as settling at organ 462 has a divergence sequence that wanders for four hundred organs and then holds within a degree and a half for the remaining seven hundred.
The wandering is not small. Before it settles the divergence at these rises swings by tens of degrees organ to organ, which is what an unsettled stem does — and then it stops, at an organ the test can name.
So the difference between a fast arrival and a slow one is how long the wandering lasts, not how gently the stem converges. That is worth knowing because a gentle convergence would make the settling time a threshold artefact and this does not.
What is worth carrying forward
Two sentences.
The first is the number: settling takes up to 290 organs at exponent three, and the qualifier belongs in the statement. Any future use of that figure — to justify a run length, to bound a transient, to argue that a stem is on its lattice — is using an exponent-three number.
The second is the shape of how it was found. A sweep run to test one prediction produced a second quantity for free, and the second quantity is where the effect was. The prediction the sweep was built for came back null, and a sweep reported only against the question it was designed around would have reported nothing.
The one line
Settling takes nothing to 290 organs at the exponent every other measurement here uses, 808 at exponent 4 and 674 at exponent 5 — a factor of 2.8 on a quantity the share of starting angles that settle cannot see, because a run arriving at organ 8 and a run arriving at organ 808 are the same entry in a share. And it is still a wall: of 72 pairs grown to 1,200 organs and then to 3,200, none settles at the longer length after failing at the shorter.
What links here
Computed from the collection, not written here: the essays that point at this one.
Shares its objects with
Essays that name at least two of the same things, and that neither author linked.
- Two regimes above a hole — both name claim testing, control, honest limits, measurement, negative result, sample size, settling time, summary statistic, transient
- A period the grid invented — both name attractor, claim testing, honest limits, measurement, negative result, the placement rule, summary statistic
- One rise per rung is a sample — both name claim testing, control, honest limits, measurement, negative result, sample size, summary statistic
- Six of six is not a measurement — both name claim testing, control, exponent, honest limits, measurement, negative result, neighbourhood depth
- The corner that does not move — both name control, honest limits, measurement, negative result, neighbourhood depth, the placement rule, summary statistic
- The panel with no corner — both name claim testing, control, honest limits, measurement, negative result, neighbourhood depth, the placement rule
Named objects
A flat tag is an object no other essay names yet.
AttractorBasinClaim testingControlExponentHonest limitsMeasurementNegative resultNeighbourhood depthThe placement ruleSample sizeSettling timeSummary statisticTransient