gram-schmidt-order
At its defaults it draws classical and modified gram–schmidt: the same subtraction, in a different order. Two panels of pseudocode differing in one argument, with the resulting pairwise dot products of the computed columns listed beneath each.
gram-schmidt-order is one function in lib/figures/ortho.js —
orthogonality — ‖qᵀq − i‖ as a measurement rather than an adjective. 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 panels of pseudocode differing in one argument, with the resulting pairwise dot products of the computed columns listed beneath each.
n: 10
The arguments are the ones A reduction that changes the order 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 panels of pseudocode differing in one argument, with the resulting pairwise dot products of the computed columns listed beneath each.
n: 8
The arguments are the ones An orthogonalisation nobody calls one 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 panels of pseudocode differing in one argument, with the resulting pairwise dot products of the computed columns listed beneath each.
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.
13 distinct claims across 3 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.
classical column 0 is still a unit vector agree — asserted 10 times
and both produce the same R to within κu
classical leaves the columns measurably non-perpendicular
while Q differs by far more than R does
Against the rule
It calls a factoriser without drawing a factorisation
(gramSchmidt),
so the rule is written down as not applying, with the reason:
prints the pairwise dot products, which is ‖QᵀQ − I‖ entry by entry
The exemption list is the interesting half of the rule rather than an escape hatch — it is
where a decision about a figure had to be argued in one line. residualcheck
refuses an exemption that is not doing work, and rejected ten of the fifteen written for the
expansion's figures on exactly that ground: a figure whose vertical axis is a residual
satisfies the rule by construction, and touching a factoriser does not by itself require an
entry.
Across the library: the rule bites on 52
of 99 generators —
37 print a residual and
15 are exempt with a published reason;
47 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 reduction that changes the order
A tall-skinny QR computed as a tree of independent block factorisations touches a 512×12 matrix once instead of twelve times, computes a completely different sequence of roundings from the sweep it replaces, and returns ‖AᵀA − RᵀR‖/‖AᵀA‖ = 1.65·10⁻¹⁵ against the sweep's 9.95·10⁻¹⁵. On the same matrix classical Gram–Schmidt returns 4.6·10⁻¹⁰.
Iterating, instead of factorisingAn orthogonalisation nobody calls one
Conjugate gradients are derived as a minimisation and behave as an orthogonalisation, which is why the finite-termination property in every textbook is not a property the method has in floating point.
Orthogonality, measuredTwo Gram–Schmidts
One argument changes. Classical Gram–Schmidt projects the original column onto each previous direction; modified projects what is left of it. In exact arithmetic the coefficients are identical. In floating point they differ by eight orders of magnitude in the thing that matters.