window-drift
At its defaults it draws how far a carried triangular factor drifts from the data, over 2976 steps of a sliding window. A window of 24 rows on 6 columns, moved one row at a time: each step folds a row in with Givens rotations and removes one with hyperbolic rotations, and the factor is never rebuilt from the rows. The rows are integers times powers of two, so AᵀA is exact in a double and the vertical axis is a distance from the answer. No single step amplifies by more than 2.72, no downdate fails, and after 2976 steps the factor is 3.87·10⁻¹⁴ from the matrix it is supposed to factor — a fitted slope of 0.554 in the step count, against a bound whose slope is 1.
window-drift is one function in lib/figures/seqstab.js —
accumulation — what a carried factor collects, and why it is a walk rather than a sum. Everything below came out of it during this build, at
arguments taken from the essays rather than invented for this page. A figure here is the
figure a reader meets in an essay, and if the generator changes, this page changes with it.
At its defaults
Drawn even though every essay passes arguments — which on this site is every essay, at 100% of placements since the standard pass. A default nothing exercises is a trap for the next essay to call this with none, and this is the page where a default that has drifted from the figures around it becomes visible.
A window of 24 rows on 6 columns, moved one row at a time: each step folds a row in with Givens rotations and removes one with hyperbolic rotations, and the factor is never rebuilt from the rows. The rows are integers times powers of two, so AᵀA is exact in a double and the vertical axis is a distance from the answer. No single step amplifies by more than 2.72, no downdate fails, and after 2976 steps the factor is 3.87·10⁻¹⁴ from the matrix it is supposed to factor — a fitted slope of 0.554 in the step count, against a bound whose slope is 1.
refresh: 0
The arguments are the ones Stable once, and three thousand times passes. A value drawn at the generator's defaults instead would be a picture no essay asked for and no assertion has been run against.
A window of 24 rows on 6 columns, moved one row at a time: each step folds a row in with Givens rotations and removes one with hyperbolic rotations, and the factor is never rebuilt from the rows. The rows are integers times powers of two, so AᵀA is exact in a double and the vertical axis is a distance from the answer. No single step amplifies by more than 2.72, no downdate fails, and after 2976 steps the factor is 3.87·10⁻¹⁴ from the matrix it is supposed to factor — a fitted slope of 0.554 in the step count, against a bound whose slope is 1.
refresh: 500
The arguments are the ones Stable once, and three thousand times passes. A value drawn at the generator's defaults instead would be a picture no essay asked for and no assertion has been run against.
A window of 24 rows on 6 columns, moved one row at a time: each step folds a row in with Givens rotations and removes one with hyperbolic rotations, and the factor is never rebuilt from the rows except every 500 steps. The rows are integers times powers of two, so AᵀA is exact in a double and the vertical axis is a distance from the answer. No single step amplifies by more than 2.72, no downdate fails, and after 2976 steps the factor is 1.27·10⁻¹⁴ from the matrix it is supposed to factor, against 3.87·10⁻¹⁴ with no refresh at all.
refresh: 100
The arguments are the ones Stable once, and three thousand times passes. A value drawn at the generator's defaults instead would be a picture no essay asked for and no assertion has been run against.
A window of 24 rows on 6 columns, moved one row at a time: each step folds a row in with Givens rotations and removes one with hyperbolic rotations, and the factor is never rebuilt from the rows except every 100 steps. The rows are integers times powers of two, so AᵀA is exact in a double and the vertical axis is a distance from the answer. No single step amplifies by more than 2.72, no downdate fails, and after 2976 steps the factor is 2.48·10⁻¹⁵ from the matrix it is supposed to factor, against 3.87·10⁻¹⁴ with no refresh at all.
refresh: 25
The arguments are the ones Stable once, and three thousand times passes. A value drawn at the generator's defaults instead would be a picture no essay asked for and no assertion has been run against.
A window of 24 rows on 6 columns, moved one row at a time: each step folds a row in with Givens rotations and removes one with hyperbolic rotations, and the factor is never rebuilt from the rows except every 25 steps. The rows are integers times powers of two, so AᵀA is exact in a double and the vertical axis is a distance from the answer. No single step amplifies by more than 2.72, no downdate fails, and after 2976 steps the factor is 8.72·10⁻¹⁹ from the matrix it is supposed to factor, against 3.87·10⁻¹⁴ with no refresh at all.
What it checked while drawing
Every figure above asserted its own claims on the way to being drawn, and a claim that failed
would have failed the build rather than drawn a wrong picture. Those assertions used to leave
no trace at all: a passing one returned true and the only evidence the figure had
checked anything was that nothing crashed. The list below is what they actually said, collected
by running this generator with an observer installed — not a description of
what it is believed to check.
9 distinct claims across 5 sets of arguments, grouped below by shape — because most of them are one sentence with a different number in it, and how many separate times that sentence was put to the test is the informative part.
a column count the exact Gram matrix stays inside a double for
a refresh period inside the range the run is drawn over
a run long enough to fit a slope
a spread of scales the integers survive
a window wider than the number of columns, or the factor is singular
and grows as the square root of the number of steps rather than in proportion to it
and the drift stays inside the bound that is linear in the steps
matmul shapes agree
no downdate in the run fails
Against the rule
The rule does not apply to it. It factorises nothing, so there is no residual it could be withholding. That is worth stating rather than leaving blank: a site that reported the rule as satisfied by every generator would be counting mostly generators the rule never reached.
Across the library: the rule bites on 113
of 238 generators —
98 print a residual and
15 are exempt with a published reason;
125 factorise nothing.
Read from lib/residual-rule.js, which is the same body the gate enforces from,
and the gate's last check fails the build if this page and it disagree about any generator.
Where it is called
Changing this generator changes every figure on this list. That is what makes the list worth publishing rather than keeping in a check script.
Stable once, and three thousand times
A sliding window adds a row and removes one at every step and never looks at the data again. No single step of it amplifies by more than 2.72, no downdate fails, and after three thousand steps the triangular factor in memory is 3.9·10⁻¹⁴ from the matrix it is supposed to be a factor of — six hundred times growth from a per-step bound that says nothing about chains.
When the problem arrives againThe problem that arrives again
A hundred and thirty essays have solved a system once and measured how wrong the answer was. Almost no computation is shaped like that. A solve is one step of an outer loop, its answer is an input rather than a deliverable, and four quantities this collection has treated as accuracy requirements turn out to be assets with a shelf life.
Iterating, instead of factorisingThe residual the method reports
Conjugate gradients prints a relative residual of 6.9·10⁻²¹. The unit roundoff is 1.1·10⁻¹⁶, so that is not a small residual and not a large one — it is not a residual. The vector the method is holding at that step has ‖b − Ax‖/‖b‖ = 5.1·10⁻¹⁰, and nothing in the run says so.
The arithmetic underneathThree walks and one bound
A left-to-right sum, a chain of three thousand rotations and a conjugate gradient residual recurrence share no arithmetic and no vocabulary. Each has a standard bound that is linear in whatever it accumulates against. All three come out at a half — 0.486, 0.554 and 0.507 — and nothing is rescaled.