sketch-draws
At its defaults it draws random numbers a sketch needs, against the number of indices, at n = 8. A dense Gaussian sketch of a mode-k unfolding multiplies an n × n^{d−1} matrix by a random one with n^{d−1} rows, so the random object is the size of the tensor divided by n — the line that crosses the tensor's own entry count at d = 2 and is 1.51·10⁸ by d = 8. A Khatri–Rao sketch replaces it with d − 1 small Gaussians per column, costing 4,032 numbers at the same point — a factor of 3.74·10⁴ — and is applied as mode products, so nothing the size of the tensor is ever formed. What it is not is Gaussian, which is what the previous figure has to measure rather than bound.
sketch-draws is one function in lib/figures/tsketch.js —
sketching a tensor — a random matrix larger than the object, and the structured one that is not. 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 dense Gaussian sketch of a mode-k unfolding multiplies an n × n^{d−1} matrix by a random one with n^{d−1} rows, so the random object is the size of the tensor divided by n — the line that crosses the tensor's own entry count at d = 2 and is 1.51·10⁸ by d = 8. A Khatri–Rao sketch replaces it with d − 1 small Gaussians per column, costing 4,032 numbers at the same point — a factor of 3.74·10⁴ — and is applied as mode products, so nothing the size of the tensor is ever formed. What it is not is Gaussian, which is what the previous figure has to measure rather than bound.
n: 8
The arguments are the ones A decomposition made only of SVDs 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 dense Gaussian sketch of a mode-k unfolding multiplies an n × n^{d−1} matrix by a random one with n^{d−1} rows, so the random object is the size of the tensor divided by n — the line that crosses the tensor's own entry count at d = 2 and is 1.51·10⁸ by d = 8. A Khatri–Rao sketch replaces it with d − 1 small Gaussians per column, costing 4,032 numbers at the same point — a factor of 3.74·10⁴ — and is applied as mode products, so nothing the size of the tensor is ever formed. What it is not is Gaussian, which is what the previous figure has to measure rather than bound.
n: 16
The arguments are the ones Sketching what is never unfolded 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 dense Gaussian sketch of a mode-k unfolding multiplies an n × n^{d−1} matrix by a random one with n^{d−1} rows, so the random object is the size of the tensor divided by n — the line that crosses the tensor's own entry count at d = 2 and is 1.93·10¹⁰ by d = 8. A Khatri–Rao sketch replaces it with d − 1 small Gaussians per column, costing 8,064 numbers at the same point — a factor of 2.4·10⁶ — and is applied as mode products, so nothing the size of the tensor is ever formed. What it is not is Gaussian, which is what the previous figure has to measure rather than bound.
n: 4
The arguments are the ones Sketching what is never unfolded 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 dense Gaussian sketch of a mode-k unfolding multiplies an n × n^{d−1} matrix by a random one with n^{d−1} rows, so the random object is the size of the tensor divided by n — the line that crosses the tensor's own entry count at d = 2 and is 1.18·10⁶ by d = 8. A Khatri–Rao sketch replaces it with d − 1 small Gaussians per column, costing 2,016 numbers at the same point — a factor of 585 — and is applied as mode products, so nothing the size of the tensor is ever formed. What it is not is Gaussian, which is what the previous figure has to measure rather than bound.
n: 6
The arguments are the ones Sketching what is never unfolded 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 dense Gaussian sketch of a mode-k unfolding multiplies an n × n^{d−1} matrix by a random one with n^{d−1} rows, so the random object is the size of the tensor divided by n — the line that crosses the tensor's own entry count at d = 2 and is 2.02·10⁷ by d = 8. A Khatri–Rao sketch replaces it with d − 1 small Gaussians per column, costing 3,024 numbers at the same point — a factor of 6665 — and is applied as mode products, so nothing the size of the tensor is ever formed. What it is not is Gaussian, which is what the previous figure has to measure rather than bound.
n: 12
The arguments are the ones Sketching what is never unfolded 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 dense Gaussian sketch of a mode-k unfolding multiplies an n × n^{d−1} matrix by a random one with n^{d−1} rows, so the random object is the size of the tensor divided by n — the line that crosses the tensor's own entry count at d = 2 and is 2.58·10⁹ by d = 8. A Khatri–Rao sketch replaces it with d − 1 small Gaussians per column, costing 6,048 numbers at the same point — a factor of 4.27·10⁵ — and is applied as mode products, so nothing the size of the tensor is ever formed. What it is not is Gaussian, which is what the previous figure has to measure rather than bound.
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 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.
the structured sketch is not larger at d = 2 — asserted 7 times
a grid the counts are meaningful at
and the dense one outgrows the tensor somewhere on this axis
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 146
of 287 generators —
131 print a residual and
15 are exempt with a published reason;
141 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 decomposition made only of SVDs
Everything the definition of tensor rank loses comes back if the SVD's algorithm is carried across instead of its definition — take the leading left singular subspace of every unfolding and project onto all of them. It exists, it costs d matrix decompositions, and its error is within √d of the best there is.
Randomised, and the guarantee that changes kindSketching what is never unfolded
A range finder multiplies its matrix by a few random vectors. For a mode-k unfolding those vectors have n^{d−1} entries, so the random object is the size of the tensor divided by n — and by six indices it is larger than the tensor it is sketching.
Randomised, and the guarantee that changes kindThe dimension does not appear
A random projection preserves the lengths of a set of vectors to within a distortion that depends on how many vectors there are and not on how many coordinates each one has. That is the fact the whole field rests on, and it is genuinely surprising.
When the index is a tupleThe format that does not notice the dimension
A Tucker core is r^d numbers, so the format that repaired the definition still cannot go past five indices. Cutting between the indices rather than across them gives d − 1 ranks instead of d, storage linear in the number of indices, and a family whose ranks are two everywhere by an addition formula.