John C. Baez's Blog, page 58

Applied Category Theory Course: Databases

 

In my online course we’re now into the third chapter of Fong and Spivak’s book Seven Sketches. Now we’re talking about databases!

To some extent this is just an excuse to (finally) introduce categories, functors, natural transformations, adjoint functors and Kan extensions. Great stuff, and databases are a great source of easy examples.

But it’s also true that Spivak helps run a company called Categorical Informatics that actually helps design databases using category theory! And his partn...

MiniBooNE

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Big news! An experiment called MiniBooNE at Fermilab in Chicago has found more evidence that neutrinos are not acting as the Standard Model says they should:

• The MiniBooNE Collaboration, Observation of a significant excess of electron-like events in the MiniBooNE short-baseline neutrino experiment.

In brief, the experiment creates a beam of muon neutrinos (or antineutrinos—they can do either one). Then they check, with a detector 541 meters away, to see if any of these particles have turne...

Workshop on Compositional Approaches

This looks great too:

• Workshop on Compositional Approaches in Physics, Natural Language Processing, and Social Sciences, 2 September 2018, Nice, France.

Compositional Approaches for Physics, NLP, and Social Sciences (CAPNS 2018) will be colocated with QI 2018. The workshop is a continuation and extension of the Workshop on Semantic Spaces at the Intersection of NLP, Physics and Cognitive Science held in June 2016.

AIMS AND SCOPE
The ability to compose parts to form a more complex whole, a...

Tropical Algebra and Railway Optimization

Simon Willerton pointed out a wonderful workshop, which unfortunately neither he nor I can attend… nor Jamie Vicary, who is at Birmingham:

• Tropical Mathematics & Optimisation for Railways, University of Birmingham, School of Engineering, Monday 18 June 2018.

If you can go, please do—and report back!

Tropical algebra involves the numbers made into a rig with minimization as the addition and addition as the multiplication. It’s called a rig because it’s a “ring without negatives”.

Tropical a...

Circuits, Bond Graphs, and Signal-Flow Diagrams

 

My student Brandon Coya finished his thesis, and successfully defended it last Tuesday!

• Brandon Coya, Circuits, Bond Graphs, and Signal-Flow Diagrams: A Categorical Perspective, Ph.D. thesis, U. C. Riverside, 2018.

It’s about networks in engineering. He uses category theory to study the diagrams engineers like to draw, and functors to understand how these diagrams are interpreted.

His thesis raises some really interesting pure mathematical questions about the category of corelations and...

RChain

guest post by Christian Williams

Mike Stay has been doing some really cool stuff since earning his doctorate. He’s been collaborating with Greg Meredith, who studied the π-calculus with Abramsky, and then conducted impactful research and design in the software industry before some big ideas led him into the new frontier of decentralization. They and a great team are developing RChain, a distributed computing infrastructure based on the reflective higher-order π-calculus, the ρ-calculus.

They’...

Applied Category Theory Course: Resource Theories

 

After a two-week break where the students did exercises, I’m back to lecturing about Fong and Spivak’s book Seven Sketches. Now we’re talking about “resource theories”. Resource theories help us answer questions like this:

Given what I have, is it possible to get what I want? Given what I have, how much will it cost to get what I want? Given what I have, how long will it take to get what I want? Given what I have, what is the set of ways to get what I want?

Resource theories in their mod...

Effective Thermodynamics for a Marginal Observer

guest post by Matteo Polettini

Suppose you receive an email from someone who claims “here is the project of a machine that runs forever and ever and produces energy for free!” Obviously he must be a crackpot. But he may be well-intentioned. You opt for not being rude, roll your sleeves, and put your hands into the dirt, holding the Second Law as lodestar.

Keep in mind that there are two fundamental sources of error: either he is not considering certain input currents (“hey, what about that ti...

Compositionality

A new journal! We’ve been working on it for a long time, but we finished sorting out some details at ACT2018, and now we’re ready to tell the world!

It’s free to read, free to publish in, and it’s about building big things from smaller parts. Here’s the top of the journal’s home page right now:

Here’s the official announcement:

We are pleased to announce the launch of Compositionality, a new diamond open-access journal for research using compositional ideas, most notably of a category-th...

Symposium on Compositional Structures

As I type this, sitting in a lecture hall at the Lorentz Center, Jamie Vicary, University of Birmingham and University of Oxford, is announcing a new series of meetings:

• Symposium on Compositional Structures.

The website, which will probably change, currently says this:

Symposium on Compositional Structures (SYCO)

The Symposium on Compositional Structures is a new interdisciplinary meeting aiming to support the growing community of researchers interested in the phenomenon of compositionali...