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Comment by noelwelsh | Hacker News Reader

Sounds similar to https://tgvaughan.github.io/sicm/toc.html Should be fun if you're physics inclined.

Official version: https://mitp-content-server.mit.edu/books/content/sectbyfn/b...

I'd really like to see a "spiritual successor" to Structure and Interpretation of Classical Mechanics--something that can take off and achieve a life of its own.

SICM is open-source, and many people have implemented their own versions of parts of it, but I would love to see a vibrant and active community develop around such a beautiful computer algebra / computer-physics system.

SICM goes far beyond simple Newtonian mechanics, implementing calculus, Lagrangian and Hamiltonian mechanics, and differential geometry, and probably a whole lot more that you just have to spelunk into the source code to discover.

(Here's a book about the differential geometry implementation in scmutils: https://mitpress.mit.edu/9780262019347/functional-differenti... as seen in HN: https://news.ycombinator.com/item?id=7884551 )

Have a look at Emmy: https://emmy.mentat.org

Are there any other systems that can render programmatic equations to LaTeX?

SymPy[1] and Mathematica[2] can both render expressions in LaTeX, if this is what you mean.

[1] https://docs.sympy.org/latest/tutorials/intro-tutorial/print...

[2] https://reference.wolfram.com/language/ref/TeXForm.html

I’m not the parent but do you know if there is a system/language that renders programmatic equations in-line in the editor? The closest thing I know of is the usage of Unicode symbols and Greek letters in Lean. I’m imagining a vscode extension that would interpret scientific code/equations and render those in-line or in a preview line above/below. Not sure about the utility of such a thing but it sure seems fun

It’s a bit of a stretch but if you write your equations in sympy in a Jupyter notebook, you can display nice LaTeX renders of the expressions and then either do math with them or just evaluate them as if you’d written them as a normal python function.

Wonder what it would take to implement a neural network in Emmy.

If it has an implementation of reverse mode automatic differentiation, then it might be possible.

I have reverse-mode (purely functional reverse mode at that!) sitting in a branch, and will get this going at some point soon. Even more fun will be compilation down to XLA, like JAX does in Python.

Really we need somehow to rejuvenate scmutils, either with a faithful port to a modern language, or a spiritual successor of similar calibre.

It's fully rejuvenated in Clojure as "Emmy", with Sussman's support and a bunch of 2D and 3D graphing extensions. See Emmy-Viewers: https://emmy-viewers.mentat.org/ and Emmy: https://emmy.mentat.org/

Thanks to https://2.maria.cloud, everything in SICM and FDG works in the browser as well: https://2.maria.cloud/gist/d3c76ee5e9eaf6b3367949f43873e8b2

Wow, thanks for this!

Of course! And referencing your other comment, during the ~2 year period I've been working on Emmy (on top of work by Colin Smith), I was keen to make the implementation more accessible and well-documented than the original.

There's still not a great map of the project (from primitives to general relativity), but many of the namespaces are written as literate programming explorations: https://emmy.mentat.org/#explore-the-project

Here's the automatic differentiation implementation/essay, for example: https://sritchie.github.io/emmy/src/emmy/differential.html

A rough sketch of the tower is:

- `emmy.value` and `emmy.generic` implement the extensible generic operations

- `emmy.ratio`, `emmy.complex` and `emmy.numbers` fleshes out the numeric tower

- `emmy.expression` and `emmy.abstract.number` add support for symbolic literals

Next we need an algebraic simplifier...

- `emmy.pattern.{match,rule,syntax} give us a pattern matching language

- `emmy.simplify.rules` adds a ton of simplification rules, out of which

- `emmy.simplify` builds a simplification engine

Actually the simplifier has three parts... the first two start in `emmy.rational-function` and `emmy.polynomial` and involve converting an expression into either a polynomial or a rational function and then back out, putting them into "canonical form" in the process. That will send you down the rabbit hole of polynomial GCD etc...

And on and on! I'm happy to facilitate any code reading journey you go on or chat about Emmy or the original scmutils, feel free to write at sam [at] mentat.org, or else visit the Discord I run for the project at https://discord.gg/hsRBqGEeQ4.

This is an absolute triumph. Over the course of several years (starting about 15 years ago) I've been looking for a way to go through SICM and FDG without dredging up an MIT scheme that's useful for nothing else, or dealing with a partial reimplementation in a language with much less expressive power.

I know someone who took that course. They did not have fond memories of it.

My impression is that it can be a very frustrating way to learn mechanics if you don't have much interest in functional programming.

It's not for everyone.

I cut my teeth on SICP before going into physics, so I was perhaps the exact target audience.

I also see Scheme as an improvement over its successor languages.

What is the appeal of functional programming for physicists?

I don't think the MIT guys have the same motivations as the author of this book. He (Walck) discusses the suitability of (a subset of) Haskell in this article: https://arxiv.org/abs/1412.4880

Maybe someone else can shed light on the MIT mindset. Certainly some of Walck's points apply to Scheme as much as to Haskell, but Scheme lacks the type system, syntax and syntactical "convenience" of curried functions. The basic strength of functional programming is the lack of complex imperative book-keeping: your code looks more like math.

My impression is that SICP and SICM are eccentric.

> Scheme lacks the type system, syntax and syntactical "convenience" of curried functions.

The argument is that all of that syntax is a distraction.

Yes, and that's like arguing that spaces between words is syntactic distraction. It's clearly not, more syntax rules can make a language simpler to understand (for both humans and computers).

The motivation to "implement" physics in code, is that you can't "cheat." You have to spell out every step in a formal way. The motivating example in SICM is that the usual way the Euler-Lagrange equations are written ... doesn't make sense.

The authors explain: "Classical mechanics is deceptively simple. It is surprisingly easy to get the right answer with fallacious reasoning or without real understanding. Traditional mathematical notation contributes to this problem. Symbols have ambiguous meanings that depend on context, and often even change within a given context."

Read the rest of the preface here: https://mitp-content-server.mit.edu/books/content/sectbyfn/b...

And why not just "code" but "functional code"? Well, it makes a lot more sense to "take a derivative of a function" if that function doesn't have side effects (etc). There is a tighter correspondence between functions in the programming sense and in the mathematical sense.

A very smart CS guy I know pitched functional programming for scientific computing- he said it would greatly speed up the performance of codes by not spending time computing results that weren't going to be used.

Although that's not a terrible idea, I have never actually seen any major scientific code that was based on functional programming and was significantly faster than its non-FP competitors. My guess is that the folks writing the codes are already pretty smart, not doing any extra work that could be easily removed, and already take advantage of algorithms that use non-functional paradigms which give them significant speedups

I've heard that before, usually from people with no experience in actual scientific computing. There's nothing wrong with using functional programming in scientific applications. I do. But I don't see how it's "specifically" good for scientific programming.

The thing about performance in scientific programming, it is often binary: You either need the very best, or you don't care about it at all. Unlike other areas of programming, there is no middle ground. If you need your scientific code to be performant, then you need to squeeze every last bit of performance out of your hardware, which you can only do with something like Fortran or C. If you don't care about performance, then it doesn't matter. That's why Python is so popular.

Ideally I would love for something like F# to replace python in the scientific computing space, but the ecosystem is so much larger in python. That's what matters to most scientists.

Generally agree, but: the idea for FP in scientific computing would be for the FP-optimizing compiler to elide any computation that doesn't contribute to the final result.

The analogy I think of is is tree traversal. A smart person can write an optimal tree traversal algorithm and make their program finish quickly, whether or not the user requested that part of the algorithm's results, but FP can realize the program doesn't output the tree, so traversing it can be skipped. OK, that's not a great analogy but the point is that in principle, FP optimization could find a cheaper way to produce the same exact values as a simulation written in a non-functional language.

How often are there competing implementations in scientific computing? Most of the time people are doing just enough to publish a paper, or maybe maintaining a single library that everyone uses. Few people have the inclination, and even fewer the funding, to "rewrite everything".

In finance, which has a lot of parallels with scientific computing but tends to end up with semi-secret, parallel, competing implementations of the same ideas, functional programming has had significant (though by no means universal) success in doing exactly what you describe.

Let's see. The two big codes I worked with- BLAST and AMBER- have competitors. For BLAST there have been a long history of codes that attempted to do better than it, and I don't think anybody really succeeded until that except possibly HMMER2. Both BLAST and HMMER2 had decades of effort poured into them. BLAST was rewritten a few times by its supporting agency (NCBI) and the author(s) of HMMER rewrote it to be HMMER2. I worked with the guy who wrote the leading competitor to HMMER, he was an independently wealthy computer programmer (with a physics background). In the case of AMBER, there are several competitors- gromacs, NAMD, and a few others are all used frequently. AMBER has been continuously developed for decades (I first used it in '95 and already it was... venerable).

All the major players in these fields read each other's code and papers and steal ideas

In other areas there are no competitors, there's just "write the minimal code to get your idea that contributes 0.01% more to scientific knowledge, publish, and then declare code bankruptcy". And a long tail of low to high quality stuff that lasts forever and turns out to be load-bearing but also completely inscrutable and unmodifiable.

After typing that out I realize I just recapitulated what you said in your first paragraph. My knowledge of finance is limited beyond knowing "jane street capital has been talking about FP for ages" and most of the people I've talked to say their work in finance (HPC mostly) is C++ or hardware-based.

What would you build / create / write if you had a web-enabled build of SICM (well, scmutils I guess) in hand? I'd love to hear more about your thoughts on how to build a community around these tools and ideas.

I would love to explore statistical mechanics, quantum field theory, and/or general relativity through a similar lens.

But I am also quite interested in learning more about the "under the hood" workings and software craftsmanship of scmutils. The textbook _uses_ scmutils to explore classical mechanics.

But it does not delve into the implementation details of scmutils itself, which interest me.

SICM Is more like a 2nd physics course as it uses the Lagrangian interpretation of classical mechanics and starts with it whereas OP seems to start from the basics.

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