order-spread
At its defaults it draws multiply-adds in three contraction networks, under the cheapest, greedy and dearest evaluation order. Every bar is an exact count and every order returns the same numbers: nothing is approximated anywhere on this picture. The matrix chain's orders run from 15,125 to 512,793,750, a factor of 3.39·10⁴. The inner product of two trains with 5 cores runs from 3,344 to 6.581·10⁹ — a factor of 1.968·10⁶, because its worst order forms the whole tensor the trains represent. The alternating-least-squares step runs from 105,120 to 113,040, a factor of 1.075, which is the counterweight: on that network the search is not worth running, and nothing about the shape of it says so in advance.
order-spread is one function in lib/figures/contract.js —
contraction order — one expression, one value, and orders that differ by two million. 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.
Every bar is an exact count and every order returns the same numbers: nothing is approximated anywhere on this picture. The matrix chain's orders run from 15,125 to 512,793,750, a factor of 3.39·10⁴. The inner product of two trains with 5 cores runs from 3,344 to 6.581·10⁹ — a factor of 1.968·10⁶, because its worst order forms the whole tensor the trains represent. The alternating-least-squares step runs from 105,120 to 113,040, a factor of 1.075, which is the counterweight: on that network the search is not worth running, and nothing about the shape of it says so in advance.
d: 5
The arguments are the ones The order decides the memory 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.
Every bar is an exact count and every order returns the same numbers: nothing is approximated anywhere on this picture. The matrix chain's orders run from 15,125 to 512,793,750, a factor of 3.39·10⁴. The inner product of two trains with 5 cores runs from 3,344 to 6.581·10⁹ — a factor of 1.968·10⁶, because its worst order forms the whole tensor the trains represent. The alternating-least-squares step runs from 105,120 to 113,040, a factor of 1.075, which is the counterweight: on that network the search is not worth running, and nothing about the shape of it says so in advance.
d: 4
The arguments are the ones The order that was right last time 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.
Every bar is an exact count and every order returns the same numbers: nothing is approximated anywhere on this picture. The matrix chain's orders run from 15,125 to 512,793,750, a factor of 3.39·10⁴. The inner product of two trains with 4 cores runs from 2,320 to 5.141·10⁷ — a factor of 2.216·10⁴, because its worst order forms the whole tensor the trains represent. The alternating-least-squares step runs from 105,120 to 113,040, a factor of 1.075, which is the counterweight: on that network the search is not worth running, and nothing about the shape of it says so in advance.
d: 3
The arguments are the ones The order the products are taken in 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.
Every bar is an exact count and every order returns the same numbers: nothing is approximated anywhere on this picture. The matrix chain's orders run from 15,125 to 512,793,750, a factor of 3.39·10⁴. The inner product of two trains with 3 cores runs from 1,296 to 4.014·10⁵ — a factor of 309.7, because its worst order forms the whole tensor the trains represent. The alternating-least-squares step runs from 105,120 to 113,040, a factor of 1.075, which is the counterweight: on that network the search is not worth running, and nothing about the shape of it says so in advance.
d: 6
The arguments are the ones The order the products are taken in 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.
Every bar is an exact count and every order returns the same numbers: nothing is approximated anywhere on this picture. The matrix chain's orders run from 15,125 to 512,793,750, a factor of 3.39·10⁴. The inner product of two trains with 6 cores runs from 4,368 to 8.424·10¹¹ — a factor of 1.928·10⁸, because its worst order forms the whole tensor the trains represent. The alternating-least-squares step runs from 105,120 to 113,040, a factor of 1.075, which is the counterweight: on that network the search is not worth running, and nothing about the shape of it says so in advance.
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.
7 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 train the network is built for
and the matrix chain's cheapest order is the textbook 15,125
and the worst order is not cheaper
nothing beats the exhaustive order on als-step
nothing beats the exhaustive order on chain
nothing beats the exhaustive order on train-inner
the train's inner product spans at least two orders of magnitude
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.
The order decides the memory
Four elimination orderings on one matrix give factors of 1,739, 1,354, 1,413 and 1,026 entries. All four factorisations are exact, all four return the same answer, and the one with the better asymptotics is not the one that wins.
Sparsity, and what elimination costsThe order that was right last time
A pivot order computed once and reused across a sequence saves the symbolic phase, and the price is that a pivot which was large may now be small. Replacing it with √u·‖A‖ costs eight orders of backward error and iterative refinement recovers a factor of 8.8 of them. Divide each row by its largest entry first and the same reuse costs nothing at all.
Where the flop count stopped predicting the timeThe order the products are taken in
The sparsity field's first essay says the elimination order decides the memory. This is the same sentence about arithmetic: a contraction of several tensors over shared indices has one value and many evaluation orders, and on the inner product of two trains they differ by a factor of two million.
Where the flop count stopped predicting the timeThe same arithmetic at a different price
A blocked and an unblocked elimination perform 72,568 operations each — the same operations, associated differently — choose the same pivots, and return a factorisation identical to the last bit: ‖PA − LU‖/‖A‖ = 4.487946226420872·10⁻¹⁶ in both. One of them moves 41,332 words between fast and slow memory and the other moves 19,476.