κ(A) and κ of the row-equilibrated matrix, along both families, n = 8
At its defaults it draws κ(a) and κ of the row-equilibrated matrix, along both families, n = 8. Write A = D·X with D diagonal and every row of X of unit norm. Every theorem about relative accuracy is a hypothesis on κ(X), and κ(A) appears in none of them — which is easy to read past and is the whole difference between the two families here. Along the graded family κ(A) climbs from 271 to 7.04·10⁵⁰ and κ(X) is 4.892 at every one of the six matrices — the grading is exactly what the diagonal factor absorbs. Along the uniform family κ(X) climbs to 3.87·10²⁵. That is the number that says which question has an answer, and it is not the number anybody prints.
scaled-classifier is one function in lib/figures/relacc.js —
relative accuracy — small compared to what, against an exact rational answer. 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.
Write A = D·X with D diagonal and every row of X of unit norm. Every theorem about relative accuracy is a hypothesis on κ(X), and κ(A) appears in none of them — which is easy to read past and is the whole difference between the two families here. Along the graded family κ(A) climbs from 271 to 7.04·10⁵⁰ and κ(X) is 4.892 at every one of the six matrices — the grading is exactly what the diagonal factor absorbs. Along the uniform family κ(X) climbs to 3.87·10²⁵. That is the number that says which question has an answer, and it is not the number anybody prints.
n: 4
The arguments are the ones A threshold the matrix does not set passes. A value nobody placed would be a picture no essay asked for and no claim was ever checked against.
Write A = D·X with D diagonal and every row of X of unit norm. Every theorem about relative accuracy is a hypothesis on κ(X), and κ(A) appears in none of them — which is easy to read past and is the whole difference between the two families here. Along the graded family κ(A) climbs from 117 to 8.38·10⁴⁹ and κ(X) is 3.372 at every one of the six matrices — the grading is exactly what the diagonal factor absorbs. Along the uniform family κ(X) climbs to 1.37·10¹¹. That is the number that says which question has an answer, and it is not the number anybody prints.
n: 12
The arguments are the ones Accurate is not a property of a method passes. A value nobody placed would be a picture no essay asked for and no claim was ever checked against.
Write A = D·X with D diagonal and every row of X of unit norm. Every theorem about relative accuracy is a hypothesis on κ(X), and κ(A) appears in none of them — which is easy to read past and is the whole difference between the two families here. Along the graded family κ(A) climbs from 4350 to 8.83·10⁴⁹ and κ(X) is 5.653 at every one of the six matrices — the grading is exactly what the diagonal factor absorbs. Along the uniform family κ(X) climbs to 1.45·10³¹. That is the number that says which question has an answer, and it is not the number anybody prints.
n: 8
The arguments are the ones Two condition numbers of one matrix passes. A value nobody placed would be a picture no essay asked for and no claim was ever checked against.
Write A = D·X with D diagonal and every row of X of unit norm. Every theorem about relative accuracy is a hypothesis on κ(X), and κ(A) appears in none of them — which is easy to read past and is the whole difference between the two families here. Along the graded family κ(A) climbs from 271 to 7.04·10⁵⁰ and κ(X) is 4.892 at every one of the six matrices — the grading is exactly what the diagonal factor absorbs. Along the uniform family κ(X) climbs to 3.87·10²⁵. That is the number that says which question has an answer, and it is not the number anybody prints.
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.
5 distinct claims across 4 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 grading of at least one bit per row, so the matrix is actually graded
a size both families can be built at
and it climbs along the uniform family
the row-equilibrated condition number does not move along the graded family
while the ordinary one runs to forty decades
Against the rule
It draws a decomposition and prints its residual. It calls
scaledCond,
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.
A threshold the matrix does not set
Two numbers come out of a relative-accuracy comparison and they belong to different things. The size of the matrix moves the constant of the routes that never fail, by a factor of 2.7 between n = 4 and n = 10; it does not move the point where the route through BᵀB stops returning an answer, which sits between ten and eleven decades of grading at every size drawn.
Eigenvalues, singular values, rankAccurate is not a property of a method
A bidiagonal matrix whose every entry is 1 or 4096 has singular values spanning thirty decades. On it, the method recommended for small singular values loses the small one by one and a half per cent, the sweep with the theorem behind it does not converge at all, and the shift the theorem is a warning about gets every value to 5·10⁻¹⁶. Nothing there contradicts the theory.
Two errors, and whose fault they areTwo condition numbers of one matrix
κ₂ is a worst case over perturbations of a given norm, and a normwise perturbation may put its whole budget on the smallest entry. The componentwise number is a worst case over perturbations proportional to the entries, which is what a backward-stable factorisation actually makes. On one matrix they are 3·10¹³ and 13.3, and the error obeys the second.