## Archive for the ‘Mathematics’ Category

### The Free Energy Principle

November 27, 2018

Below is a link to a fascinating article about Karl Friston, whose research on the “free energy principle” (also known as active inference) tries to explain how biological (or even artificial) systems maintain or even increase their organization. Without much explanation, here are some details. The model is a system with four main variables:

• Sense (s)
• Action (a)
• Internal States (r or μ)
• Hidden States (ψ)

Sense and action divide the internal states of the system from the hidden states external to it. This division is called a “Markov Blanket”. I’ve tried to show the equations between the variables correctly but I’m not too sure if I have them right. They seem to change from paper to paper. F is an expression of the free energy, but I’m not sure what f is at the moment, except for being some sort of “flow”.

https://www.wired.com/story/karl-friston-free-energy-principle-artificial-intelligence/

https://en.wikipedia.org/wiki/Free_energy_principle

https://en.wikipedia.org/wiki/Markov_blanket

http://rsif.royalsocietypublishing.org/content/15/138/20170792

[*11.6]

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### Viete’s Method of Constructing Pythagorean Triples

October 24, 2018

Number is the ruler of forms and ideas, and the cause of gods and daemons.

— Pythagoras, as attributed by Iamblichus

This diagram shows (but not to scale ;-)) a clever method of constructing two Pythagorean triples given any two other Pythagorean triples due to Francois Viete.

Given (a, b, c, d, e, f are integers):

a^2 + b^2 = c^2
d^2 + e^2 = f^2

two other triples are found by synaeresis:

A = ae + bd

and diaeresis:

D = ae – bd

(I guess a, b, d, and e can always be picked so that B > 0 and D > 0, that is, be > ad and ae > bd?)

so that:

A^2 + B^2 = (cf)^2
D^2 + E^2 = (cf)^2

Voila!

https://en.wikipedia.org/wiki/Pythagorean_triple

Special thanks to Pat’s Blog for this little gem:

https://pballew.blogspot.com/2018/10/viete-on-pythagorean-triples.html

Additionally, these relationships are also used in Fermat’s Theorem on sums of 2 squares

https://en.wikipedia.org/wiki/Proofs_of_Fermat%27s_theorem_on_sums_of_two_squares

[*9.138, *10.186, *10.187]

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### Science, Technology, Engineering, and Mathematics

June 14, 2018

STEM: Science, Technology, Engineering, and Mathematics. We often hear that these areas of education and expertise are critical for the development of our modern society. To attract students to these fields, banners and logos are full of bright colors and crisp graphics. In comparison, above is my rather dull diagram. Not very enticing, is it?

Some are now adding Arts to the four, giving STEAM. I think the Arts are important of course, but fives don’t go with my oeuvre.

In addition, I give you a diagram with Chinese substituted for English (科學 技術 工程 數學).

https://en.wikipedia.org/wiki/Science,_technology,_engineering,_and_mathematics

[*10.110]

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### Fourier Analysis, V2

December 8, 2017

Here is another example of a fourfold, in the mathematics of Fourier Analysis. Here the four elements of our investigation resolve into Discrete Time, Continuous Time, the Fourier Series, and the Fourier Transform.

From the three dualities of Time – Frequency, Periodic – Aperiodic, and Discrete – Continuous, we obtain the four combinations Discrete Time/Periodic Frequency, Continuous Time/Aperiodic Frequency, the Fourier Series (Periodic Time/Discrete Frequency), and the Fourier Transform (Aperiodic Time/Continuous Frequency).

In the table below, T stands for Time and f for Frequency. The subscripts denote the attributes of each: D for Discrete, C for Continuous, P for Periodic, and A for Aperiodic. So T subscript C, f subscript A means that when Time is Continuous, Frequency is Aperiodic, etc. Please see Steve Tjoa’s web site for the equations for the Fourier Series and the Fourier Transform in Continuous and Discrete Time.References:

http://stevetjoa.com/633

http://en.wikipedia.org/wiki/Fourier_analysis

http://en.wikipedia.org/wiki/Fourier_series

http://en.wikipedia.org/wiki/Fourier_transform

[*7.74, *7.108]

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### A Rosetta Stone

December 6, 2017

Abstract of Physics, Topology, Logic and Computation: A Rosetta Stone by John Baez and Michael Stay:

In physics, Feynman diagrams are used to reason about quantum processes. In the 1980s, it became clear that underlying these diagrams is a powerful analogy between quantum physics and topology: namely, a linear operator behaves very much like a “cobordism”. Similar diagrams can be used to reason about logic, where they represent proofs, and computation, where they represent programs. With the rise of interest in quantum cryptography and quantum computation, it became clear that there is extensive network of analogies between physics, topology, logic and computation. In this expository paper, we make some of these analogies precise using the concept of “closed symmetric monoidal category”. We assume no prior knowledge of category theory, proof theory or computer science.

• Physics
• Logic
• Topology
• Computation

Perhaps Category Theory is a “Fifth Essence”?

http://math.ucr.edu/home/baez/rosetta/rose3.pdf

https://arxiv.org/abs/0903.0340

[*9.168, *10.50]

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### The Duality of Time and Information, V3

October 1, 2017

The states of a computing system bear information and change time, while its events bear time and change information.

from The Duality of Time and Information by Vaughn Pratt

The most promising transformational logic seems to us to be Girard’s linear logic.

— from Rational Mechanics and Natural Mathematics by Vaughn Pratt

Here we have three duals:

• Information – Time
• States – Events
• Bear – Change

Vaughan Pratt / The Duality of Time and Information http://boole.stanford.edu/pub/dti.pdf

Vaughan Pratt / Time and Information in Sequential and Concurrent Computation http://boole.stanford.edu/pub/tppp.pdf

Vaughan Pratt / Rational Mechanics and Natural Mathematics http://chu.stanford.edu/guide.html#ratmech

[*5.170]

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### Buy One Get One Free

May 6, 2016

Speaking of paradoxes, the Banach-Tarski Paradox is an interesting theorem in mathematics that claims that a solid 3-dimensional ball can be decomposed into a finite number of parts, which can then be reassembled in a different way (by using translation and rotation of the parts but no scaling is needed) to create two identical copies of the original structure. The theorem works by allowing the parts of the decomposition to be rather strange.

One of the important ingredients of the theorem’s proof is finding a “paradoxical decomposition” of the free group on two generators. If F is such a free group with generators a and b, and S(a) is the infinite set of all finite strings that start with a but without any adjacency of a and its inverse (a^-1) or similarly b and b^-1, and 1 is the empty (identity) string, then

F = 1 + S(a) + S(b) + S(a^-1) + S(b^-1)

But also note that

F = aS(a^-1) + S(a)

F = bS(b^-1) + S(b)

So F can be paradoxically decomposed into two copies of itself by using just two of the four S()’s for each copy. Both aS(a^-1) and bS(b^-1) contain the empty string, so I’m not sure what happens to the original one. One might think that aS(a^-1) is “bigger” than S(a) but they are actually both countably infinite and so are the same “size”.

The generators a and b are then set to be certain 3-dimensional isometries (distance preserving transformations which include translation and rotation). The rest of the theorem requires further constructions that may be of interest, as well as needing the Axiom of Choice or something like it. It is also curious that the paradox fails to work in dimensions of 1 or 2.

The diagram above tries to list the beginning of each of the sets S(a), S(b), S(a^-1), and S(b^-1). The empty string can be thought to occupy the center of the diagram but it is either not shown because it is empty, or it is shown as being empty. Alternatively one could create a more general fourfold with the aspects of structure, (paradoxical) decomposition, parts, and reassembly.

References:

https://en.wikipedia.org/wiki/Axiom_of_choice

http://faculty.mccneb.edu/jdlee3/thesisonline.pdf

[*9.124, *9.125]

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### Propositions as Types

February 14, 2016

For almost 100 years, there have been linkages forged between certain notions of logic and of computation. As more associations have been discovered, the bonds between the two have grown stronger and richer.

• Propositions in logic can be considered equivalent to types in programming languages.
• Proofs of propositions in logic can be considered equivalent to programs of given type in computation.
• The simplification of proofs of propositions in logic can be considered equivalent to the evaluation of programs of types in computation.

The separate work of various logicians and computer scientists (and their precursors) can be paired:

• Gerhard Gertzen’s work on proofs in intuitionistic natural deduction and Alonzo Church’s work on the simply typed lambda calculus.
• J. Roger Hindley and Robin Milner’s work on type systems for combinatory logic and programming languages, respectively.
• J. Y. Girard and John Reynold’s work on the second order lambda calculus and parametric polymorphic programs, respectively.
• Haskell Curry’s and W. A. Howard’s work on the overall correspondence between these notions of proofs as programs or positions as types.

Logic and computation are the sequential chains of efficient causation and actions. Propositions and types are the abstract grids of formal causation and structures. Proofs and programs are the normative cycles of final causation and functions. Simplification and evaluation are the reductive solids of material causation and parts.

References:

Philip Wadler / Propositions as Types, in Communications of the ACM, Vol. 58 No. 12 (Dec 2015) Pages 75-85.

http://cacm.acm.org/magazines/2015/12/194626-propositions-as-types/fulltext

Preprint at

Also see:

https://en.wikipedia.org/wiki/Hindley%E2%80%93Milner_type_system

https://en.wikipedia.org/wiki/System_F

https://en.wikipedia.org/wiki/Curry%E2%80%93Howard_correspondence

[*9.92-9.94]

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### Four Transformations of Chu Spaces

November 29, 2015

Can mathematics help us reformulate Cartesian Dualism? I have previously tried to diagram some of computer scientist Vaughn Pratt’s notions, such as a Duality of Time and Information and the Stone Gamut. Another recent attempt is the diagram above of four transformations that issue out of his analysis of Chu Spaces. Pratt’s conceptualization of these generalized topological spaces led him to propose a mathematization of mind and body dualism.

The duality of time and information was actually an interplay of several dualities, such as the aforementioned time and information, plus states and events, and changing and bearing (or dynamic and static). The philosophical mathematization in his paper “Rational Mechanics and Natural Mathematics” leads to additional but somewhat different dualities, shown in the following table:

 Mind Body Mental Physical States Events Anti-functions Functions Anti-sets Sets Operational Denotational Infers Impresses Logical Causal Against time With time Menu Object Contingent Necessary

Pratt reveals two transformations that are “mental”: delete and copy, and two that are “physical”: adjoin and identify.

These four transformations are functions and their converses which:

• Identify when the function is not injective.
• Adjoin when the function is not surjective.
• Copy when the converse is not injective.
• Delete when the converse is not surjective.

Ordinarily we think of mind and body as being radically different in kind, but perhaps they are the same but merely viewed from a different perspective or direction. Recall what Heraclitus says, “the road up and the road down are the same thing”.

References:

https://en.wikipedia.org/wiki/Dualism_%28philosophy_of_mind%29

http://boole.stanford.edu/pub/ratmech.pdf

http://chu.stanford.edu/

http://en.wikipedia.org/wiki/Chu_space

[*6.74, *6.75, *9.76]

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### Bayes’ Rule

October 10, 2015

Bayes’ Rule or Theorem or Law. Because, why not?

P(B) P(A|B) = P(A) P(B|A)

References:

https://en.wikipedia.org/wiki/Bayes’_theorem

[*6.132, *9.48]

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