Hacker News: keithalewis

New comment by keithalewis in "I fed 24 years of my blog posts to a Markov model"

keithalewis — Mon, 15 Dec 2025 02:12:54 +0000

https://math.uchicago.edu/~shmuel/Network-course-readings/MC...

New comment by keithalewis in "A wild 'freakosystem' has been born in Hawaii"

keithalewis — Thu, 10 Apr 2025 22:21:09 +0000

I see what you did there.

New comment by keithalewis in "Introduction to Stochastic Calculus"

keithalewis — Mon, 24 Feb 2025 19:32:08 +0000

There is no need for it. Here is a simple replacement: https://keithalewis.github.io/math/um1.html.

New comment by keithalewis in "Beej's Guide to Git"

keithalewis — Mon, 10 Feb 2025 12:21:18 +0000

Linus wrote it, so there's got to be a pony in there somewhere. He's the first person in the world to figure out version control software. /s

New comment by keithalewis in "Beej's Guide to Git"

keithalewis — Mon, 10 Feb 2025 05:15:40 +0000

Thank you for your diligence in explaining complicated topics in a way that makes them accessible to people trying to learn what people before them figured out. You are a true educator that seems have found a place to support you to continue doing that.

Are you concerned that your git exposition is much longer than the other guides you have produced?

New comment by keithalewis in "The Tensor Cookbook (2024)"

keithalewis — Sun, 02 Feb 2025 05:15:48 +0000

The Wikipedia page on this is sufficient. If F:X -> Y is a function between normed linear spaces then DF:X -> L(X,Y), where L(X,Y) is the vector space of linear operators from X to Y, satisfies F(x + h) = F(x) + DF(x)h + o(h). A function is differentiable if it can be locally approximated by a linear operator.

Some confusion arises from the difference between f:R -> R and f':R -> R. It's Fréchet derivative is Df:R -> L(R,R) where Df(x)h = f'(x)h. Row vectors and column vectors a just a clumsy way of thinking about this.

BTW, all you need in order to publish on arixv.org is to know a FoF. There is no rigorous peer review. https://arxiv.org/abs/1912.01091, https://arxiv.org/abs/2009.10852.

New comment by keithalewis in "The Tensor Cookbook (2024)"

keithalewis — Sat, 01 Feb 2025 03:29:20 +0000

"This book aims to standardize the notation for tensor diagrams..." https://youtu.be/zELbzXAmcUA?t=73

New comment by keithalewis in "The Tensor Cookbook (2024)"

keithalewis — Sat, 01 Feb 2025 03:15:32 +0000

The author also seems to be unaware of Fréchet derivatives.

New comment by keithalewis in "The Tensor Cookbook (2024)"

keithalewis — Fri, 31 Jan 2025 21:38:22 +0000

This is incomplete, incorrect, and irrelevant. Standard notation already exists. I'm sure it is fun to draw squiggly lines and some people enjoy reinventing the wheel. Spend some time learning what others have taught us before striking out on your own lonely path.

New comment by keithalewis in "Kalman Filter Tutorial"

keithalewis — Sun, 19 Jan 2025 18:27:04 +0000

Your statement "the best path forward for me understanding is a path that can maintain that curiosity" comes off as entitled. Only you owe yourself that.

"I can play with Arnold's cat and, slowly, through no scientific rigor..." You are fooling yourself into believing you understand if you leave out rigor. If your post has the words "I" and "me" in every other sentence, maybe you should consider whether or not you are adding value for others in the online discussion.

I doesn't cost you anything to ask other people to do things for you, and you will no doubt find other thoughtless people chiming in about your right to do that. If everything you need is not at your fingertips already, maybe no amount of handholding will help.

New comment by keithalewis in "The CAP theorem of Clustering: Why Every Algorithm Must Sacrifice Something"

keithalewis — Fri, 27 Dec 2024 09:24:18 +0000

Let S = {1, 2}. Every distance function is determined by d(1,2) = a, a >= 0. Define f(d) = {{1,2}} if a = 0 and f(d) = {{1},{2}} otherwise. Isn't this a clustering algorithm that is scale invariant, rich, and consistent?

New comment by keithalewis in "Quiver: A Modern Commutative Diagram Editor"

keithalewis — Fri, 27 Dec 2024 08:10:05 +0000

You made a completely obvious and true statement starting with "It would help..." That seems to be frowned upon on HN.

BTW, a simpler definition of a (small) category is that it is a partial monoid.

New comment by keithalewis in "Crystal Ball Trading Game"

keithalewis — Mon, 16 Dec 2024 00:25:33 +0000

We agree. The case was about Renaissance breaking the law. The best lawyers their money could buy lost and did not avail themselves of their right to appeal. The ruling body found they were tax cheats.

Philanthropic work is great way to get shills to come out of the woodworks.

New comment by keithalewis in "When a Crystal Ball Isn't Enough to Make You Rich"

keithalewis — Sun, 15 Dec 2024 13:11:32 +0000

Worked for Renaissance Technologies: https://www.ft.com/content/8cef8c70-5d02-4762-9100-2d92d0c76...

New comment by keithalewis in "Category Theory in Programming"

keithalewis — Sat, 14 Dec 2024 01:09:06 +0000

Category theory is just another way of looking at math besides the impoverished notion "everything is a set". Mathematics is used in computer science. Rust is a great example. Jean-Yves Girard invented linear logic to make Gerhard Gentzen's sequent calculus symmetric, similar to Paul Dirac's theory that led to the discovery of positrons. Girard's concern about using a proposition exactly once in a proof led to borrow checking.

Putting on category theory glasses can help discover and clarify new facts. Thinking in terms of objects and arrows leads to duality: reverse the direction of the arrows.

The category Set is only one of many categories. The objects are sets and the arrows are functions. A function I -> S that is 1-1/injective/mono[1] corresponds to the set theory notion of a "subset". The dual is a function S -> I that is onto/surjective/epi[2]. What set theory notion does this correspond to?

Hint: Look into David Ellerman. He is the von Neumann of our times.

[1] f is mono if fg = fh implies g = h. [2] f is epi if gf = hf implies g = h.

Hi Dang.

New comment by keithalewis in "Parkinson's Law: It’s real, so use it"

keithalewis — Thu, 12 Dec 2024 14:08:52 +0000

This. Motivation is the key to getting employees to produce over a period of time. Give the good ones the maximum amount of ownership they can handle and they will set an example for everyone else. Grow the talent over time.

Fire the whinny shit-talkers as soon as possible. They drag everyone down.

New comment by keithalewis in "Timemap.org – Interactive Map of History"

keithalewis — Thu, 12 Dec 2024 13:03:09 +0000

And, like, a LARPing mode I could use while sitting in my mom's basement that would automagically post every brain fart I had to HN. That would be totally cool!

New comment by keithalewis in "The Rules of Programming (2023)"

keithalewis — Mon, 09 Dec 2024 10:04:44 +0000

When I worked at Bloomberg their first coding guideline was "Don't sweat the small stuff." I was mystified by that when I first read it. Then I sat in meetings where someone would drone on about how clever they thought their code was until someone asked "Is this small stuff?" It would shut them up so we could move on to more important matters.

New comment by keithalewis in "Square roots and maxima"

keithalewis — Sat, 30 Nov 2024 18:57:36 +0000

Front page material? P(max{X_1, X_2} <= x) = P(X_1 <= x, X_2 <= x) = P(X_1 <= x) P(X_2 <= x) = xx. P(sqrt(X_3) <= x) = P(X_3 <= x^2) = x^2. It is late in the day when midgets cast long shadows.

New comment by keithalewis in "Time-series forecasting through recurrent topology"

keithalewis — Sun, 24 Nov 2024 12:19:09 +0000

You are missing what is missing. Their source code does not fill in the missing pieces.