partition-degeneracy
At its defaults it draws one graph, nudged by 10⁻¹², and 3 different partitions. Three seven-vertex cliques joined in a triangle by three single edges, one of whose conductances is raised by 0. When all three are equal the graph has a three-fold symmetry, λ₂ and λ₃ coincide — measured here at a gap of 1.72·10⁻¹⁵ — and there is no Fiedler vector: there is a plane, and every unit vector in it is an exact eigenvector. Eight runs on this graph with its edge weights nudged by a relative 10⁻¹² — four orders above the rounding, and far below anything anybody would call a difference in the data — return 3 distinct partitions, at conductances 0.0455. All of them are correct answers to the relaxation, and on a symmetric graph they are equally good ones. Which one a library returns is decided by its starting vector, and the site has an essay about a plane surviving what its vectors do not.
partition-degeneracy is one function in lib/figures/graphlap.js —
the matrix a graph makes — row sums that are exactly zero, a count that is a threshold, and a partition with no vector. 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.
Three seven-vertex cliques joined in a triangle by three single edges, one of whose conductances is raised by 0. When all three are equal the graph has a three-fold symmetry, λ₂ and λ₃ coincide — measured here at a gap of 1.72·10⁻¹⁵ — and there is no Fiedler vector: there is a plane, and every unit vector in it is an exact eigenvector. Eight runs on this graph with its edge weights nudged by a relative 10⁻¹² — four orders above the rounding, and far below anything anybody would call a difference in the data — return 3 distinct partitions, at conductances 0.0455. All of them are correct answers to the relaxation, and on a symmetric graph they are equally good ones. Which one a library returns is decided by its starting vector, and the site has an essay about a plane surviving what its vectors do not.
skew: 0
The arguments are the ones A bound with a square root in it 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.
Three seven-vertex cliques joined in a triangle by three single edges, one of whose conductances is raised by 0. When all three are equal the graph has a three-fold symmetry, λ₂ and λ₃ coincide — measured here at a gap of 1.72·10⁻¹⁵ — and there is no Fiedler vector: there is a plane, and every unit vector in it is an exact eigenvector. Eight runs on this graph with its edge weights nudged by a relative 10⁻¹² — four orders above the rounding, and far below anything anybody would call a difference in the data — return 3 distinct partitions, at conductances 0.0455. All of them are correct answers to the relaxation, and on a symmetric graph they are equally good ones. Which one a library returns is decided by its starting vector, and the site has an essay about a plane surviving what its vectors do not.
skew: 0.001
The arguments are the ones A partition decided in the last digit 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.
Three seven-vertex cliques joined in a triangle by three single edges, one of whose conductances is raised by 0.001. When all three are equal the graph has a three-fold symmetry, λ₂ and λ₃ coincide — measured here at a gap of 1.85·10⁻⁴ — and there is no Fiedler vector: there is a plane, and every unit vector in it is an exact eigenvector. Eight runs on this graph with its edge weights nudged by a relative 10⁻¹² — four orders above the rounding, and far below anything anybody would call a difference in the data — return 1 distinct partition, at conductances 0.0455. All of them are correct answers to the relaxation, and on a symmetric graph they are equally good ones. Which one a library returns is decided by its starting vector, and the site has an essay about a plane surviving what its vectors do not.
skew: 0.01
The arguments are the ones A partition decided in the last digit 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.
Three seven-vertex cliques joined in a triangle by three single edges, one of whose conductances is raised by 0.01. When all three are equal the graph has a three-fold symmetry, λ₂ and λ₃ coincide — measured here at a gap of 0.00185 — and there is no Fiedler vector: there is a plane, and every unit vector in it is an exact eigenvector. Eight runs on this graph with its edge weights nudged by a relative 10⁻¹² — four orders above the rounding, and far below anything anybody would call a difference in the data — return 1 distinct partition, at conductances 0.0455. All of them are correct answers to the relaxation, and on a symmetric graph they are equally good ones. Which one a library returns is decided by its starting vector, and the site has an essay about a plane surviving what its vectors do not.
skew: 0.05
The arguments are the ones A partition decided in the last digit 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.
Three seven-vertex cliques joined in a triangle by three single edges, one of whose conductances is raised by 0.05. When all three are equal the graph has a three-fold symmetry, λ₂ and λ₃ coincide — measured here at a gap of 0.00916 — and there is no Fiedler vector: there is a plane, and every unit vector in it is an exact eigenvector. Eight runs on this graph with its edge weights nudged by a relative 10⁻¹² — four orders above the rounding, and far below anything anybody would call a difference in the data — return 1 distinct partition, at conductances 0.0455. All of them are correct answers to the relaxation, and on a symmetric graph they are equally good ones. Which one a library returns is decided by its starting vector, and the site has an essay about a plane surviving what its vectors do not.
skew: 0.2
The arguments are the ones A partition decided in the last digit 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.
Three seven-vertex cliques joined in a triangle by three single edges, one of whose conductances is raised by 0.2. When all three are equal the graph has a three-fold symmetry, λ₂ and λ₃ coincide — measured here at a gap of 0.0355 — and there is no Fiedler vector: there is a plane, and every unit vector in it is an exact eigenvector. Eight runs on this graph with its edge weights nudged by a relative 10⁻¹² — four orders above the rounding, and far below anything anybody would call a difference in the data — return 1 distinct partition, at conductances 0.0455. All of them are correct answers to the relaxation, and on a symmetric graph they are equally good ones. Which one a library returns is decided by its starting vector, and the site has an essay about a plane surviving what its vectors do not.
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 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.
a graph with at least two vertices
a perturbation small enough to keep the two halves symmetric
a positive weight
every endpoint inside the vertex set
Jacobi needs a symmetric matrix
no edge given twice
no self-loop
Against the rule
It draws a decomposition and prints its residual. It calls
laplacianEig, fiedler,
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 214
of 382 generators —
194 print a residual and
20 are exempt with a published reason;
168 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 bound with a square root in it
Cheeger's inequality brackets a graph's best cut between λ₂/2 and √(2λ₂). The lower bound is attained exactly. The upper one is loose by a factor of fourteen — on the one graph in the census with a real bottleneck, which is the shape it is always quoted about.
The matrix that is a graphA partition decided in the last digit
On a graph with a symmetry there is no Fiedler vector — there is a plane, and every vector in it is an exact eigenvector. Twenty-four runs with the edge weights nudged by 10⁻¹² return ten different partitions of a cycle and, on a hypercube, two different qualities of answer.
The matrix that is a graphA ranking whose order is not determined
Of the fourteen adjacent comparisons in a top-fifteen, fourteen survive perturbing the arithmetic at the rounding level, eleven survive moving the teleportation parameter across its usual range, and three survive removing one link. The computation is the strongest part of the answer.
The matrix that is a graphThe spectrum is not the graph
Two graphs on six vertices with the same Laplacian characteristic polynomial — as integer polynomials, not to fourteen digits. One contains a triangle; the other is bipartite. Every method in this field that reads only the spectrum is answering about the class.
The matrix that is a graphThe vector that has to be rounded
A spectral partition is an eigenvector, and an eigenvector is a real vector. The answer wanted is a subset. Something has to turn one into the other, and the something is a heuristic applied after the linear algebra has finished.