What one weighted Jacobi sweep does to each mode, at ω = 0.67
At its defaults it draws what one weighted jacobi sweep does to each mode, at ω = 0.67. A curve of the damping factor against mode frequency, falling from one at the left through zero and towards minus one at the right. The right-hand half of the plot is shaded, and two horizontal lines mark the worst damping inside it.
smoothing-spectrum is one function in lib/figures/multigrid.js —
multigrid — the smoother, the coarse grid, and the rate that does not move. 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 curve of the damping factor against mode frequency, falling from one at the left through zero and towards minus one at the right. The right-hand half of the plot is shaded, and two horizontal lines mark the worst damping inside it.
omega: 0.5
The arguments are the ones A smoother that stops being one passes. A value nobody placed would be a picture no essay asked for and no claim was ever checked against.
A curve of the damping factor against mode frequency, falling from one at the left through zero and towards minus one at the right. The right-hand half of the plot is shaded, and two horizontal lines mark the worst damping inside it.
omega: 0.6667
The arguments are the ones The error smoothing cannot reach passes. A value nobody placed would be a picture no essay asked for and no claim was ever checked against.
A curve of the damping factor against mode frequency, falling from one at the left through zero and towards minus one at the right. The right-hand half of the plot is shaded, and two horizontal lines mark the worst damping inside it.
omega: 1
The arguments are the ones The error smoothing cannot reach passes. A value nobody placed would be a picture no essay asked for and no claim was ever checked against.
A curve of the damping factor against mode frequency, falling from one at the left through zero and towards minus one at the right. The right-hand half of the plot is shaded, and two horizontal lines mark the worst damping inside it.
omega: 0.3
The arguments are the ones The error smoothing cannot reach passes. A value nobody placed would be a picture no essay asked for and no claim was ever checked against.
A curve of the damping factor against mode frequency, falling from one at the left through zero and towards minus one at the right. The right-hand half of the plot is shaded, and two horizontal lines mark the worst damping inside it.
omega: 0.8
The arguments are the ones The error smoothing cannot reach passes. A value nobody placed would be a picture no essay asked for and no claim was ever checked against.
A curve of the damping factor against mode frequency, falling from one at the left through zero and towards minus one at the right. The right-hand half of the plot is shaded, and two horizontal lines mark the worst damping inside it.
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.
14 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.
mode 1 is damped by the factor its frequency predicts agree — checked 12 times
the smoothest mode survives whatever ω is
the smoothing factor, scanned and in closed form agree
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 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 smoother that stops being one
Weighted Jacobi's smoothing factor on the convection–diffusion operator is a function of the cell Péclet number and nothing else — identical to eight digits at five grid sizes at matched Pe. It is 0.3335 at Pe = 0.016, exactly 1/√2 at Pe = 1, and 5.2190 at Pe = 7.8, where the sweep amplifies the modes it exists to remove.
Iterating, instead of factorisingThe error smoothing cannot reach
One weighted Jacobi sweep multiplies every mode of the error by a number, and the number is a sine. Half the modes are cut by three or better, and the other half come back at 0.999 — which is not a failure of the method but the fact the whole of multigrid is built on.