two blocks with 1 arc back: where a walk spends its time, against where the arcs are
At its defaults it draws two blocks with 1 arc back: where a walk spends its time, against where the arcs are. Two distributions over the 24 vertices of a two blocks with 1 arc back. The taller bar at each vertex is the stationary distribution of the random walk, computed by 824 power iterations with no subtraction anywhere and checked against Pᵀφ = φ at 9.69·10⁻¹⁵; the narrower one is the out-degree divided by the total, which is what an undirected intuition reaches for. They differ by up to 0.0616, which is 62 per cent of the largest entry. The difference is what makes a directed normalised Laplacian a global object: the degree of a vertex is local and how often a walk visits it is not.
stationary-vs-degree is one function in lib/figures/digraph.js —
arrows — a laplacian that is not symmetric, and the walk that has to be computed before it can be. 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 distributions over the 24 vertices of a two blocks with 1 arc back. The taller bar at each vertex is the stationary distribution of the random walk, computed by 824 power iterations with no subtraction anywhere and checked against Pᵀφ = φ at 9.69·10⁻¹⁵; the narrower one is the out-degree divided by the total, which is what an undirected intuition reaches for. They differ by up to 0.0616, which is 62 per cent of the largest entry. The difference is what makes a directed normalised Laplacian a global object: the degree of a vertex is local and how often a walk visits it is not.
family: "blocks", n: 24
The arguments are the ones A conductance the arcs do not measure 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 distributions over the 24 vertices of a two blocks with 1 arc back. The taller bar at each vertex is the stationary distribution of the random walk, computed by 824 power iterations with no subtraction anywhere and checked against Pᵀφ = φ at 9.69·10⁻¹⁵; the narrower one is the out-degree divided by the total, which is what an undirected intuition reaches for. They differ by up to 0.0616, which is 62 per cent of the largest entry. The difference is what makes a directed normalised Laplacian a global object: the degree of a vertex is local and how often a walk visits it is not.
family: "balanced", n: 32
The arguments are the ones A conductance the arcs do not measure 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 distributions over the 32 vertices of a balanced digraph on 32. The taller bar at each vertex is the stationary distribution of the random walk, computed by 388 power iterations with no subtraction anywhere and checked against Pᵀφ = φ at 1.01·10⁻¹⁴; the narrower one is the out-degree divided by the total, which is what an undirected intuition reaches for. On this family they agree to 1.64·10⁻¹⁴, because the digraph is balanced and the closed form says they must. That is the second route the whole construction is checked by.
family: "strong", n: 24
The arguments are the ones A conductance the arcs do not measure 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 distributions over the 24 vertices of a random strongly connected on 24. The taller bar at each vertex is the stationary distribution of the random walk, computed by 157 power iterations with no subtraction anywhere and checked against Pᵀφ = φ at 7.76·10⁻¹⁵; the narrower one is the out-degree divided by the total, which is what an undirected intuition reaches for. They differ by up to 0.0806, which is 70 per cent of the largest entry. The difference is what makes a directed normalised Laplacian a global object: the degree of a vertex is local and how often a walk visits it is not.
family: "cycle", n: 24
The arguments are the ones A conductance the arcs do not measure 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 distributions over the 24 vertices of a directed cycle on 24. The taller bar at each vertex is the stationary distribution of the random walk, computed by 1 power iterations with no subtraction anywhere and checked against Pᵀφ = φ at 0; the narrower one is the out-degree divided by the total, which is what an undirected intuition reaches for. On this family they agree to 2.08·10⁻¹⁷, because the digraph is balanced and the closed form says they must. That is the second route the whole construction is checked by.
family: "symmetric", n: 24
The arguments are the ones A conductance the arcs do not measure 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 distributions over the 24 vertices of a symmetric digraph on 24. The taller bar at each vertex is the stationary distribution of the random walk, computed by 51 power iterations with no subtraction anywhere and checked against Pᵀφ = φ at 3.53·10⁻¹⁵; the narrower one is the out-degree divided by the total, which is what an undirected intuition reaches for. On this family they agree to 2.23·10⁻¹⁵, because the digraph is balanced and the closed form says they must. That is the second route the whole construction is checked by.
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 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 balanced digraph's stationary vector IS its degree distribution
a digraph small enough to draw a vertex at a time
a digraph with at least two vertices
a family the library builds
and an unbalanced one's is not
and every entry of it is nonnegative, as a probability must be
and it is stationary, checked against Pᵀφ = φ
arcs inside the vertex set
every entry of a stationary distribution is nonnegative
no repeated arc
no self-loops
positive arc weights
the power iteration reached a stationary vector
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 214
of 397 generators —
194 print a residual and
20 are exempt with a published reason;
183 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 conductance the arcs do not measure
Symmetrising a directed Laplacian with respect to its walk recovers everything the arrows took — a real spectrum, a sweep cut, a Cheeger inequality. What it does not recover is the quantity: the inequality bounds the probability that a step of the walk crosses the cut, which on one graph here is three times the weight of the arcs that do.
The matrix that is a graphA Laplacian that is not symmetric
Point the edges and the matrix stops being symmetric. Its row sums are still exactly zero, so the null vector survives; everything built on the quadratic form does not, and the eigenvalues need a plane rather than a line. Asymmetry permits that and does not force it, which the smallest case here demonstrates by being asymmetric and real.