The pair read from the angles
Worth reading first: Counting the spirals · A head is a set of points.
This site was built on one rule. A spiral count is evidence only when it comes out of the point positions, by machinery that has never been shown the divergence angle; a count derived from the angle is a restatement of what the pattern was built from and proves nothing.
That rule has been applied to published claims about sunflowers and pine cones and to models from the literature. It has not, until now, been applied to a reading taken inside this collection’s own libraries — and applied there, it catches one.
Where the disagreement turned up
Not by looking for it. The depth thread’s panels compare two rules at a fixed rise, and a check on whether a larger jostle destroys the lattice needed every stem counted rather than assumed. Counting them turned up a column that did not match.
The check counts from the points: take the last two hundred organs of a run, hand their positions to a counter that receives no angle, and read the pair. Every stem, at every exponent from 1.5 to 6, at every seed and every jostle up to a degree, comes back 5/8 — the pair the rise carries.
The thread’s own pair column does not match. That column is read from the
divergence sequence — the run’s angles, one per organ — and for the deepest
rule it comes back 5/7, at every seed and every jostle.
What the two readers actually do
Worth setting out, because “counted from the points” and “read from the angles” are phrases doing a lot of work.
The point counter takes a set of positions on a cylinder, builds the neighbour relations between them, and finds the runs of organs that lie along a common direction. The number of such runs in each of the two dominant directions is the pair. Nothing in it references a divergence, a rise or a lattice model; it would return a pair for a set of points scattered by hand, and on a disordered set it returns nothing rather than something.
The angle reader takes the sequence of divergences and asks which whole numbers, used as steps through the sequence, produce the tightest clustering of angles. On a lattice the answer is the two contact numbers, because stepping p organs at a time lands on nearly the same azimuth every time — that is what a parastichy is, expressed in the sequence rather than in the picture.
The second is a real measurement of a real property and it is much cheaper than the first. Its weakness is that “tightest clustering under a step of k” is a property of any structure with a period, and a lattice is only one such structure.
Which is wrong, and how to tell
The reading from the angles, and there are three independent ways to see it.
The geometry. At this rise and this divergence the seven-step is about three times the length of the eight-step. A pair of five and seven is not a near miss between two nearly equal candidates; the seven-family is nowhere near the bottom of the length ranking, so no lattice here has it as a contact family.
The divergence. Across all five exponents the settled divergence moves by 0.118°. If the deep rule were on a different lattice its divergence would be somewhere else, and a tenth of a degree is not somewhere else.
The positions. The counter is shown the arrangement and returns 5/8. That is the measurement this site’s whole premise says to prefer, and it is unanimous across every run.
So five rules, one lattice, and one instrument returning a different answer for one of them.
Why the angle reader fails there and nowhere else
The reader works by looking for a comb in the sequence of divergences — a periodicity, in effect — and turning it into a pair. On a stem whose angles are independent from organ to organ, the comb it finds is the lattice’s.
The deepest rule’s stems are not that. A rule with a slow falloff reads a very large neighbourhood, so its response to a disturbance is spread over many organs and its divergence sequence carries correlations running out to a hundred organs. That correlation is a structure in the sequence, and it is not the lattice’s structure.
So the reader is resolving a periodicity that belongs to the rule’s memory rather than to the arrangement of organs, and reporting it as a family. Its failure is specific: the four shallower rules produce sequences with little memory, and the reader gets those right.
Why it matters more than a wrong column
Because the site’s premise says exactly this and the machinery quietly did not.
The premise was stated against other people’s claims: a caption saying a sunflower has thirty-four spirals, based on a model built from the golden angle, is a restatement rather than a count. Nobody expected the same failure inside a library here, because the libraries were written by somebody who knew the rule.
What made it possible is that the angle reader was never used as a count. It was a convenience column — a quick label on a run, printed in a table so a reader could see at a glance what kind of stem each row was. Convenience columns do not get checked against the instrument they are shortcuts for, and this one has been wrong on one row of every depth table for four rounds.
Nothing in the thread’s conclusions rests on it, which is worth saying plainly. The drift-through quantity, the neighbourhood depths, the crossings — none reads the pair. The column was decoration. But a decoration that contradicts the site’s own premise is worth a page, because the next person to reach for it might not be reaching for decoration.
The two readings are not interchangeable in general
That is the useful generalisation, and it is worth separating from the specific bug.
Reading a pair from the angles is legitimate when the angles are what is available — which is the situation with a published sequence of divergences and no photograph, and it is the situation this collection is in with several literature claims. The reader is not wrong as a method.
What it is is sensitive to structure in the sequence that is not the lattice. Memory in the divergences is one such structure. So is a periodicity in the growth rate, which this collection has already shown can forge a comb that a reader will report as a pair.
The two cases are the same failure from opposite directions. There, a disturbance with a period forged a comb the arrangement did not have. Here, a rule with a memory forged a comb the arrangement did not have. Both were caught by counting from the points, and the earlier one was caught deliberately while this one was caught by a check run for another purpose entirely.
What it would have taken to catch it earlier
Nothing clever, and that is the annoying part.
The two readers have both been in this collection since its second phase, and they have never been run on the same stems. The point counter is used where a count is a result — the sunflower work, the cylinder round trip, the ablation census — and the angle reader is used where a pair is a label, in tables whose subject is something else. There was no place in the code where both were called on one run, so there was nothing to disagree.
Running them together on one stem costs a second. Running them together on every stem of a table costs a minute. Neither was done because neither was anybody’s question — the label was a label, and a label that looked plausible drew no attention to itself.
The general fix is the one this collection keeps arriving at from different directions: where two instruments measure the same quantity, run both and print both. Two implementations of one measurement is exactly how a disagreement becomes visible, and exactly how a stale column stays hidden when only one of them runs.
What was fixed
The check now runs where the panels are built: every cell of every lifted panel counts its stems from the positions and asserts they carry the rise’s own pair. That is a gate on the argument rather than a note in a docstring, and it would fail the build if a future amplitude destroyed the lattice.
The angle-read column is kept and reported beside the counted one rather than removed. Removing it would hide the disagreement, and the disagreement is the interesting part: a stem whose divergence sequence reads as 5/7 while its positions read as 5/8 is a stem with a measurable memory, and the disagreement is a diagnostic for exactly the property the depth thread is about.
The rule restated, since it has now bitten twice
The premise is usually stated as advice about other people’s claims. It is worth restating as a rule about instruments, because that is the form in which it catches things.
A count is evidence when the instrument producing it could have returned a different answer for the same subject built a different way. A counter shown positions could return anything; a reader shown a divergence sequence generated from a divergence will return that divergence’s pair, whatever the arrangement is. The premise is not really about angles versus positions — it is about whether the instrument has any independence from the thing being claimed.
Put that way it applies here without any special pleading. The angle reader is independent of the lattice — nobody handed it a divergence — but it is not independent of the rule’s memory, and the memory is what the depth thread is about. An instrument that is contaminated by the very quantity a thread is studying is the worst case, and it is the case that occurred.
The version of this that would be a real problem
Everything above is a decoration column and a lesson. It is worth asking what the same failure would look like if it were load-bearing, because that is the version worth guarding against.
It would look like a claim of the form this arrangement is counted at p and q, where the count came from a sequence rather than from a picture, and where the sequence had structure in it from the process that generated it. On this site the nearest thing to that is the jugacy work, which asks whether a stem’s counts share a factor and therefore whether the pattern arrives several organs at a time.
That work counts from the positions and measures rotational symmetry on the positions too, which is why a false result there was caught: a counter shown a wrecked stem and a genuinely two-at-a-time stem side by side returned the same pair for both, and the symmetry measurement separated them. Had the counting been done from the angles, a stem with a periodic memory would have read as jugate and there would have been nothing to catch it with.
So the answer to “does this matter” is: not here, and it would have mattered a great deal one thread over. The premise earns its keep by being applied everywhere rather than where it seems necessary, which is the argument for applying it to convenience columns too.
What is left
Whether the disagreement is quantitative. It appears at exponent 1.5 and not at 2, and the neighbourhood depths at those two exponents are 182 organs and 120 — not a large gap. So somewhere between them the angle reader stops being fooled, and where that is might be a usable measure of how much memory a sequence has to carry before its comb is unreadable.
There is also a cheap experiment in it. If the reader is fooled by memory in the sequence, then feeding it a sequence with a stated memory and no lattice at all should make it report a pair — which is the forgery experiment this collection has already built, run against a different question. Pointing it at this one is a matter of reading a different column out of runs that exist.
And whether any published claim in this subject has the same defect. A divergence sequence read for its pair is a common enough thing in the literature, and a plant with a slow-responding meristem would produce exactly the correlated sequence that fools this reader. Nothing here can settle that, because it would need sequences of real divergences at a length nobody has published — which is the survey this site cannot do, in one more form.
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.
- A period the grid invented — both name artefact, claim testing, divergence angle, honest limits, measurement, parastichy pair, resolution, summary statistic
- The slide a counter holds constant — both name counting blind, claim testing, divergence angle, honest limits, lattice, measurement, parastichy pair, summary statistic
- What a count cannot decide — both name counting blind, claim testing, divergence angle, honest limits, lattice, measurement, parastichy pair, summary statistic
- A band that holds the angle still — both name artefact, counting blind, divergence angle, lattice, measurement, parastichy pair, resolution
- A dip belongs to the head — both name artefact, divergence angle, honest limits, lattice, measurement, resolution, summary statistic
- A disturbance with a memory — both name artefact, autocorrelation, divergence angle, honest limits, lattice, measurement, parastichy pair
Named objects
A flat tag is an object no other essay names yet.
ArtefactAutocorrelationCounting blindClaim testingContinued fractionCounting radiusDivergence angleExponentHonest limitsLatticeMeasurementParastichy pairResolutionSummary statistic