kernel-spectra
At its defaults it draws the singular values of one off-diagonal block, for four kernels on the same 96 points. Two intervals that do not touch — [0, 1] and [2, 3] — and the 96 × 96 block between them, for four kernels. 1/r falls a factor of 52 a column and is below 10⁻⁸ after 5; log r behaves the same way, for the reason the expansion makes obvious. An independent draw per entry gives 96 singular values above 10⁻⁸ out of 96, on the same size and the same density, which is what makes the other curves a measurement rather than a property of sorted numbers. The block has full algebraic rank in every case; what differs is where the numbers stop mattering, and that is a decision rather than a fact about the matrix.
kernel-spectra is one function in lib/figures/kernel.js —
one block — where a matrix with no zero entries turns out to have five useful columns. 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.
Two intervals that do not touch — [0, 1] and [2, 3] — and the 96 × 96 block between them, for four kernels. 1/r falls a factor of 52 a column and is below 10⁻⁸ after 5; log r behaves the same way, for the reason the expansion makes obvious. An independent draw per entry gives 96 singular values above 10⁻⁸ out of 96, on the same size and the same density, which is what makes the other curves a measurement rather than a property of sorted numbers. The block has full algebraic rank in every case; what differs is where the numbers stop mattering, and that is a decision rather than a fact about the matrix.
n: 96
The arguments are the ones A block nobody can call sparse 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.
Two intervals that do not touch — [0, 1] and [2, 3] — and the 96 × 96 block between them, for four kernels. 1/r falls a factor of 52 a column and is below 10⁻⁸ after 5; log r behaves the same way, for the reason the expansion makes obvious. An independent draw per entry gives 96 singular values above 10⁻⁸ out of 96, on the same size and the same density, which is what makes the other curves a measurement rather than a property of sorted numbers. The block has full algebraic rank in every case; what differs is where the numbers stop mattering, and that is a decision rather than a fact about the matrix.
n: 32
The arguments are the ones A block nobody can call sparse 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.
Two intervals that do not touch — [0, 1] and [2, 3] — and the 32 × 32 block between them, for four kernels. 1/r falls a factor of 53 a column and is below 10⁻⁸ after 5; log r behaves the same way, for the reason the expansion makes obvious. An independent draw per entry gives 32 singular values above 10⁻⁸ out of 32, on the same size and the same density, which is what makes the other curves a measurement rather than a property of sorted numbers. The block has full algebraic rank in every case; what differs is where the numbers stop mattering, and that is a decision rather than a fact about the matrix.
n: 256
The arguments are the ones A block nobody can call sparse 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.
Two intervals that do not touch — [0, 1] and [2, 3] — and the 256 × 256 block between them, for four kernels. 1/r falls a factor of 52 a column and is below 10⁻⁸ after 5; log r behaves the same way, for the reason the expansion makes obvious. An independent draw per entry gives 256 singular values above 10⁻⁸ out of 256, on the same size and the same density, which is what makes the other curves a measurement rather than a property of sorted numbers. The block has full algebraic rank in every case; what differs is where the numbers stop mattering, and that is a decision rather than a fact about the matrix.
n: 128
The arguments are the ones A limit the matrix never reaches 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.
Two intervals that do not touch — [0, 1] and [2, 3] — and the 128 × 128 block between them, for four kernels. 1/r falls a factor of 52 a column and is below 10⁻⁸ after 5; log r behaves the same way, for the reason the expansion makes obvious. An independent draw per entry gives 128 singular values above 10⁻⁸ out of 128, on the same size and the same density, which is what makes the other curves a measurement rather than a property of sorted numbers. The block has full algebraic rank in every case; what differs is where the numbers stop mattering, and that is a decision rather than a fact about the matrix.
n: 64
The arguments are the ones A rank that is a number of digits 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.
Two intervals that do not touch — [0, 1] and [2, 3] — and the 64 × 64 block between them, for four kernels. 1/r falls a factor of 52 a column and is below 10⁻⁸ after 5; log r behaves the same way, for the reason the expansion makes obvious. An independent draw per entry gives 64 singular values above 10⁻⁸ out of 64, on the same size and the same density, which is what makes the other curves a measurement rather than a property of sorted numbers. The block has full algebraic rank in every case; what differs is where the numbers stop mattering, and that is a decision rather than a fact about the matrix.
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.
5 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 block size the decomposition is affordable at
a block size the dense SVD below is affordable at
a kernel this file defines
and the block of independent draws is not
the smooth kernel's block is numerically low rank at eight digits
Against the rule
It draws a decomposition and prints its residual. It calls
spectraByKernel,
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 141
of 264 generators —
126 print a residual and
15 are exempt with a published reason;
123 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.
A block nobody can call sparse
A 96 × 96 block of a kernel matrix has ninety-six nonzero singular values and five that matter. It has no zero entries, it is not described by fewer numbers than it contains, and neither of the two ways this collection already knows to make a large matrix affordable applies to it.
Structure, and the solver that cannot see itA limit the matrix never reaches
Szegő's theorem gives a Toeplitz family's condition number in closed form — ((1+ρ)/(1−ρ))², which is 81 at ρ = 0.8. The 8×8 section reaches 52% of it, the 128×128 reaches 98.9%, and none of them ever arrives. A statement about a family is not a statement about the matrix in front of you.
Neither sparse nor denseA rank that is a number of digits
Ask a kernel block for two digits and it costs two columns; ask for fourteen and it costs nine. The curve is a straight line at 0.55 columns a decade, and the bound the geometry gives is a straight line too — at 3.32, which is the same shape and six times the price.
Eigenvalues, singular values, rankRank is a decision
A floating-point matrix does not have a rank. It has a spectrum of singular values, and somewhere in that spectrum is a place where the values stop being signal and start being noise. Deciding where is a judgement, and the evidence for it is a gap.
Sparsity, and what elimination costsThe fill that is not independent
Eliminate both halves of a grid and what is left on the separator is 100 per cent nonzero — the sparsity field's result, unchanged. Its off-diagonal block is 11 by 12 and six columns describe it to eight digits. Renumber the separator and the same block needs all eleven.
Neither sparse nor denseThe kernel with nothing to compress
Hold the geometry fixed at q = ½, fix the wavelength, and scale the picture up by sixteen. A smooth kernel needs six columns at every scale. An oscillatory one needs twelve, sixteen, twenty-two, thirty-three, fifty-three, and there is no scale at which it stops.
Structure, and the solver that cannot see itThe matrix that is one row
A circulant of size 16 is sixteen numbers, has no zero entry anywhere, and hands over its entire spectrum in closed form — the discrete Fourier transform of its first column, exactly. An eigensolver spends a sweep of Jacobi rotations over 256 entries arriving at the same answer, and agrees to 1.2·10⁻¹⁵.
Neither sparse nor denseThe same matrix, numbered twice
One symmetric permutation. The condition number is 24.3948 either way to eight digits and the Frobenius norm is 6.13996414·10³ either way to twelve. The partition that stored 27,008 numbers now finds no admissible pair anywhere and stores all 65,536, and the format that compresses regardless stores 118,208.
Neither sparse nor denseThe size the rank does not notice
Sample a kernel block at 32, 64, 128 and 256 points a side and it needs five columns, five, five and five. Sample the touching block next to it at the same four sizes and it needs nine, eleven, twelve and thirteen. Same kernel, same accuracy, one number and a logarithm.