A randomised rank-k solve, 4 seeds a rank
At its defaults it draws a randomised rank-k solve, 4 seeds a rank. Relative error against the rank kept, on a logarithmic vertical axis, with a vertical bar at each rank spanning the seeds. The band is 1.84 wide at rank 8, where the method is at its worst, and 1.022 wide at rank 24, where it is at its best. The same computation on the same data returns a different answer each time.
rank-band is one function in lib/figures/compose.js —
four knobs — one floor under them, and a fifth that is not a knob at all. 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.
Relative error against the rank kept, on a logarithmic vertical axis, with a vertical bar at each rank spanning the seeds. The band is 1.84 wide at rank 8, where the method is at its worst, and 1.022 wide at rank 24, where it is at its best. The same computation on the same data returns a different answer each time.
seeds: 4
The arguments are the ones An answer that changes with the seed passes. A value nobody placed would be a picture no essay asked for and no claim was ever checked against.
Relative error against the rank kept, on a logarithmic vertical axis, with a vertical bar at each rank spanning the seeds. The band is 1.84 wide at rank 8, where the method is at its worst, and 1.022 wide at rank 24, where it is at its best. The same computation on the same data returns a different answer each time.
noise: 0.1
The arguments are the ones An answer that changes with the seed passes. A value nobody placed would be a picture no essay asked for and no claim was ever checked against.
Relative error against the rank kept, on a logarithmic vertical axis, with a vertical bar at each rank spanning the seeds. The band is 1.81 wide at rank 8, where the method is at its worst, and 1.095 wide at rank 12, where it is at its best. The same computation on the same data returns a different answer each time.
noise: 0.001
The arguments are the ones An answer that changes with the seed passes. A value nobody placed would be a picture no essay asked for and no claim was ever checked against.
Relative error against the rank kept, on a logarithmic vertical axis, with a vertical bar at each rank spanning the seeds. The band is 1.84 wide at rank 8, where the method is at its worst, and 1.004 wide at rank 28, where it is at its best. The same computation on the same data returns a different answer each time.
n: 96
The arguments are the ones An answer that changes with the seed passes. A value nobody placed would be a picture no essay asked for and no claim was ever checked against.
Relative error against the rank kept, on a logarithmic vertical axis, with a vertical bar at each rank spanning the seeds. The band is 2.02 wide at rank 4, where the method is at its worst, and 1.010 wide at rank 28, where it is at its best. The same computation on the same data returns a different answer each time.
seeds: 3
The arguments are the ones An answer that changes with the seed passes. A value nobody placed would be a picture no essay asked for and no claim was ever checked against.
Relative error against the rank kept, on a logarithmic vertical axis, with a vertical bar at each rank spanning the seeds. The band is 1.71 wide at rank 8, where the method is at its worst, and 1.007 wide at rank 24, where it is at its best. The same computation on the same data returns a different answer each time.
What it checked while drawing
Every figure above checked its own claims on the way to being drawn, and a claim that failed
would have stopped the picture rather than shipped a wrong one. Those checks 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.
6 distinct claims across 6 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 size the randomised solve is affordable at
and barely at all at the optimum
enough seeds for a band and few enough to draw
matmul shapes agree
the seed changes the answer somewhere in the range
with the spread worst where the method is worst
Against the rule
It draws a decomposition and prints its residual. It calls
rankSweep,
and every figure above carries the badge — which residualcheck verifies by looking
for it in the emitted SVG rather than by finding the call that builds one. A badge that is
constructed and then left out of the body is the failure that check exists for.
Across the library: the rule bites on 217
of 397 generators —
199 print a residual and
18 are exempt with a published reason;
180 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.
An answer that changes with the seed
A randomised rank-k solve is a truncation computed in a random subspace, and it reaches the same floor as the deterministic ones. What it does not do is return the same answer twice — a factor of 1.84 across four seeds at rank 8, and 1.02 at the rank where the method is best.
Eigenvalues, singular values, rankAn eigenvalue with no value
If the second matrix of a pencil is singular then some of the eigenvalues are infinite, and that is not a degeneracy — it is the algebraic constraints of the model, one per constraint. What survives is a pair of numbers rather than one, and on the line those pairs live on, infinity is an ordinary point with an ordinary residual.
Eigenvalues, singular values, rankThe best approximation there is
The error of the best rank-k approximation is not bounded by the next singular value. It is equal to it. That is an unusually sharp theorem, and it makes the theorem itself usable as an independent check on the computation.