inverse-sides

At its defaults it draws ‖ax̂ − i‖ and ‖x̂a − i‖ for a computed hilbert inverse, to n = 12. Two residuals of the same computed inverse, each divided by ‖A‖‖X̂‖ so both are dimensionless. The exact inverse satisfies both to zero. The computed one satisfies ‖AX̂ − I‖ at 3.5·10⁻¹⁸ — the side its columns were solved along — and ‖X̂A − I‖ at 6.8·10⁻¹⁶, 195 times larger, at n = 12. Each column of X̂ is the exact solution of a slightly perturbed system, but a different perturbation for each column, so there is no single nearby matrix whose inverse X̂ is.

inverse-sides is one function in lib/figures/inverse.js — the inverse — an object almost nobody needs, and the backward error of forming it. 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.

Two residuals of the same computed inverse, each divided by ‖A‖‖X̂‖ so both are dimensionless. The exact inverse satisfies both to zero. The computed one satisfies ‖AX̂ − I‖ at 3.5·10⁻¹⁸ — the side its columns were solved along — and ‖X̂A − I‖ at 6.8·10⁻¹⁶, 195 times larger, at n = 12. Each column of X̂ is the exact solution of a slightly perturbed system, but a different perturbation for each column, so there is no single nearby matrix whose inverse X̂ is.

Two residuals of the same computed inverse, each divided by ‖A‖‖X̂‖ so both are dimensionless. The exact inverse satisfies both to zero. The computed one satisfies ‖AX̂ − I‖ at 3.5·10⁻¹⁸ — the side its columns were solved along — and ‖X̂A − I‖ at 6.8·10⁻¹⁶, 195 times larger, at n = 12. Each column of X̂ is the exact solution of a slightly perturbed system, but a different perturbation for each column, so there is no single nearby matrix whose inverse X̂ is.

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 2 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 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 92 of 198 generators — 77 print a residual and 15 are exempt with a published reason; 106 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.