Generator

mcmillan-degree

One function in the lti library, called 10 times across 6 essays. Below: what it draws at its defaults, what it draws at every value an essay asks for, the 12 claims it put to the test while drawing them, and where it stands against the rule this site is named for.

At its defaults it draws two rank decisions for one integer: the mcmillan degree of a 40-state model. Singular values, each divided by the largest of its own set. The Loewner matrix is built from 32 samples of H on the imaginary axis and never touches A: its 6th singular value stands 9.46·10⁴ above the next, so the rank decision is not a close call. The Hankel matrix of Markov parameters CAᵏB is built from A, B and C — strictly more information — and has no cliff, because ‖A‖ is (n+1)² and its entries span 3·10³⁷. It returns 2 where the answer is 6. The definition is not the algorithm, and the route with less information is the one that works.

mcmillan-degree is one function in lib/figures/lti.js — a model that is a rational function — the degree that is a rank, by two routes that disagree. 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 rank decisions for one integer: the McMillan degree of a 40-state modelSingular values, each divided by the largest of its own set. The Loewner matrix is built from 32 samples of H on the imaginary axis and never touches A: its 6th singular value stands 9.46·10⁴ above the next, so the rank decision is not a close call. The Hankel matrix of Markov parameters CAᵏB is built from A, B and C — strictly more information — and has no cliff, because ‖A‖ is (n+1)² and its entries span 3·10³⁷. It returns 2 where the answer is 6. The definition is not the algorithm, and the route with less information is the one that works.1357911131510⁻¹⁸10⁻¹⁵10⁻¹²10⁻⁹10⁻⁶10⁻³1indexsingular value ÷ the largestdegree 6from samples of Hfrom A, B and Cone integer, two routesstates40Loewner rank6its gap9.5·10⁴Markov rank2its dynamic range3·10³⁷the rank of a divided differenceand the rank that cannot be seen

Singular values, each divided by the largest of its own set. The Loewner matrix is built from 32 samples of H on the imaginary axis and never touches A: its 6th singular value stands 9.46·10⁴ above the next, so the rank decision is not a close call. The Hankel matrix of Markov parameters CAᵏB is built from A, B and C — strictly more information — and has no cliff, because ‖A‖ is (n+1)² and its entries span 3·10³⁷. It returns 2 where the answer is 6. The definition is not the algorithm, and the route with less information is the one that works.

n: 40

The arguments are the ones A basis that is the same subspace and not the same thing 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 rank decisions for one integer: the McMillan degree of a 40-state modelSingular values, each divided by the largest of its own set. The Loewner matrix is built from 32 samples of H on the imaginary axis and never touches A: its 6th singular value stands 9.46·10⁴ above the next, so the rank decision is not a close call. The Hankel matrix of Markov parameters CAᵏB is built from A, B and C — strictly more information — and has no cliff, because ‖A‖ is (n+1)² and its entries span 3·10³⁷. It returns 2 where the answer is 6. The definition is not the algorithm, and the route with less information is the one that works.1357911131510⁻¹⁸10⁻¹⁵10⁻¹²10⁻⁹10⁻⁶10⁻³1indexsingular value ÷ the largestdegree 6from samples of Hfrom A, B and Cone integer, two routesstates40Loewner rank6its gap9.5·10⁴Markov rank2its dynamic range3·10³⁷the rank of a divided differenceand the rank that cannot be seen

Singular values, each divided by the largest of its own set. The Loewner matrix is built from 32 samples of H on the imaginary axis and never touches A: its 6th singular value stands 9.46·10⁴ above the next, so the rank decision is not a close call. The Hankel matrix of Markov parameters CAᵏB is built from A, B and C — strictly more information — and has no cliff, because ‖A‖ is (n+1)² and its entries span 3·10³⁷. It returns 2 where the answer is 6. The definition is not the algorithm, and the route with less information is the one that works.

n: 12

The arguments are the ones A model that is a rational function 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 rank decisions for one integer: the McMillan degree of a 12-state modelSingular values, each divided by the largest of its own set. The Loewner matrix is built from 32 samples of H on the imaginary axis and never touches A: its 6th singular value stands 9.53·10⁵ above the next, so the rank decision is not a close call. The Hankel matrix of Markov parameters CAᵏB is built from A, B and C — strictly more information — and has no cliff, because ‖A‖ is (n+1)² and its entries span 2.7·10³⁶. It returns 2 where the answer is 6. The definition is not the algorithm, and the route with less information is the one that works.1357911131510⁻¹⁸10⁻¹⁵10⁻¹²10⁻⁹10⁻⁶10⁻³1indexsingular value ÷ the largestdegree 6from samples of Hfrom A, B and Cone integer, two routesstates12Loewner rank6its gap9.5·10⁵Markov rank2its dynamic range2.7·10³⁶the rank of a divided differenceand the rank that cannot be seen

Singular values, each divided by the largest of its own set. The Loewner matrix is built from 32 samples of H on the imaginary axis and never touches A: its 6th singular value stands 9.53·10⁵ above the next, so the rank decision is not a close call. The Hankel matrix of Markov parameters CAᵏB is built from A, B and C — strictly more information — and has no cliff, because ‖A‖ is (n+1)² and its entries span 2.7·10³⁶. It returns 2 where the answer is 6. The definition is not the algorithm, and the route with less information is the one that works.

n: 20

The arguments are the ones A model that is a rational function 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 rank decisions for one integer: the McMillan degree of a 20-state modelSingular values, each divided by the largest of its own set. The Loewner matrix is built from 32 samples of H on the imaginary axis and never touches A: its 6th singular value stands 3.51·10⁵ above the next, so the rank decision is not a close call. The Hankel matrix of Markov parameters CAᵏB is built from A, B and C — strictly more information — and has no cliff, because ‖A‖ is (n+1)² and its entries span 1.4·10³⁷. It returns 2 where the answer is 6. The definition is not the algorithm, and the route with less information is the one that works.1357911131510⁻¹⁸10⁻¹⁵10⁻¹²10⁻⁹10⁻⁶10⁻³1indexsingular value ÷ the largestdegree 6from samples of Hfrom A, B and Cone integer, two routesstates20Loewner rank6its gap3.5·10⁵Markov rank2its dynamic range1.4·10³⁷the rank of a divided differenceand the rank that cannot be seen

Singular values, each divided by the largest of its own set. The Loewner matrix is built from 32 samples of H on the imaginary axis and never touches A: its 6th singular value stands 3.51·10⁵ above the next, so the rank decision is not a close call. The Hankel matrix of Markov parameters CAᵏB is built from A, B and C — strictly more information — and has no cliff, because ‖A‖ is (n+1)² and its entries span 1.4·10³⁷. It returns 2 where the answer is 6. The definition is not the algorithm, and the route with less information is the one that works.

n: 80

The arguments are the ones A model that is a rational function 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 rank decisions for one integer: the McMillan degree of a 80-state modelSingular values, each divided by the largest of its own set. The Loewner matrix is built from 32 samples of H on the imaginary axis and never touches A: its 6th singular value stands 2.91·10⁴ above the next, so the rank decision is not a close call. The Hankel matrix of Markov parameters CAᵏB is built from A, B and C — strictly more information — and has no cliff, because ‖A‖ is (n+1)² and its entries span 3.7·10³⁷. It returns 2 where the answer is 6. The definition is not the algorithm, and the route with less information is the one that works.1357911131510⁻¹⁸10⁻¹⁵10⁻¹²10⁻⁹10⁻⁶10⁻³1indexsingular value ÷ the largestdegree 6from samples of Hfrom A, B and Cone integer, two routesstates80Loewner rank6its gap2.9·10⁴Markov rank2its dynamic range3.7·10³⁷the rank of a divided differenceand the rank that cannot be seen

Singular values, each divided by the largest of its own set. The Loewner matrix is built from 32 samples of H on the imaginary axis and never touches A: its 6th singular value stands 2.91·10⁴ above the next, so the rank decision is not a close call. The Hankel matrix of Markov parameters CAᵏB is built from A, B and C — strictly more information — and has no cliff, because ‖A‖ is (n+1)² and its entries span 3.7·10³⁷. It returns 2 where the answer is 6. The definition is not the algorithm, and the route with less information is the one that works.

n: 60

The arguments are the ones A model that is a rational function 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 rank decisions for one integer: the McMillan degree of a 60-state modelSingular values, each divided by the largest of its own set. The Loewner matrix is built from 32 samples of H on the imaginary axis and never touches A: its 6th singular value stands 7.4·10⁴ above the next, so the rank decision is not a close call. The Hankel matrix of Markov parameters CAᵏB is built from A, B and C — strictly more information — and has no cliff, because ‖A‖ is (n+1)² and its entries span 3.5·10³⁷. It returns 2 where the answer is 6. The definition is not the algorithm, and the route with less information is the one that works.1357911131510⁻¹⁸10⁻¹⁵10⁻¹²10⁻⁹10⁻⁶10⁻³1indexsingular value ÷ the largestdegree 6from samples of Hfrom A, B and Cone integer, two routesstates60Loewner rank6its gap7.4·10⁴Markov rank2its dynamic range3.5·10³⁷the rank of a divided differenceand the rank that cannot be seen

Singular values, each divided by the largest of its own set. The Loewner matrix is built from 32 samples of H on the imaginary axis and never touches A: its 6th singular value stands 7.4·10⁴ above the next, so the rank decision is not a close call. The Hankel matrix of Markov parameters CAᵏB is built from A, B and C — strictly more information — and has no cliff, because ‖A‖ is (n+1)² and its entries span 3.5·10³⁷. It returns 2 where the answer is 6. The definition is not the algorithm, and the route with less information is the one that works.

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.

12 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 degree the sampling can resolve

a degree the state dimension can carry

a division by a complex number that is not zero

a grid fine enough to have modes and coarse enough to draw

a state dimension the sweep can afford

an actuator and a sensor on the grid

an even number of samples, at least four

and the Markov-parameter rank is not

enough Markov parameters for the block asked for

LU is for square matrices

matmul shapes agree

the Loewner rank is the degree that was built in

Against the rule

It draws a decomposition and prints its residual. It calls loewnerDegree, markovDegree, 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 192 of 346 generators — 174 print a residual and 18 are exempt with a published reason; 154 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.

Reduction, and what a model is for

A basis that is the same subspace and not the same thing

The interpolation conditions are conditions on a subspace, so any basis of it will do. The one a derivation writes down reaches a condition number of 7.7·10⁹ by its eighth vector, and the rate at which it gets there is set by a number the user chose with no information.

Reduction, and what a model is for

A model that is a rational function

A state matrix has a hundred thousand rows and the thing anyone wants from it is a function of one complex variable. The number that says how much of that size was ever the complexity is a rank — and the rank a derivation writes down cannot be computed, while one built from samples alone can.

Reduction, and what a model is for

Exact at the points that were named

Balanced truncation asks for nothing and bounds everything, at a cost no large model can pay. The other kind of reduction asks for r numbers, costs r solves, is exact at every one of them — and bounds nothing anywhere else. That trade is the whole of large-scale model reduction.

Reduction, and what a model is for

Interpolating at the model’s own poles

One choice of interpolation points is not arbitrary — the mirrored poles of the model about to be built. It is a fixed point rather than a guess, and when it is reached it beats a method costing O(n³) — by 0.4 per cent, which is the honest size of the whole contest.

Reduction, and what a model is for

The bound that is known in advance

Almost every error on this site is measured after the fact. Balanced truncation has one that is computable before the reduced model exists, in a norm of a function rather than of a residual — and on ordinary problems it is not an upper bound that is loose. It is attained.

Reduction, and what a model is for

The product nobody had to form

The Hankel singular values are the square roots of the eigenvalues of PQ. Form that product and half of them stop existing, at a floor this site can predict from one number — and the fix is the one the least-squares field has had since its first essay, arriving in a place with no least-squares problem in it.

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