Hacker News: aap_

New comment by aap_ in "Vector Meson Dominance"

aap_ — Sun, 05 Apr 2026 12:40:47 +0000

If you're rotating around your fingers you're doing something else, not what i mean. I'm just talking palm up, rotating in the vertical axis, 720°. like the cup dance.

New comment by aap_ in "Vector Meson Dominance"

aap_ — Fri, 03 Apr 2026 20:43:10 +0000

The whole assumption of the video is that one cannot understand spinors. He does a good job with the mathematics but i disagree with the premise.

New comment by aap_ in "Vector Meson Dominance"

aap_ — Fri, 03 Apr 2026 20:41:33 +0000

Sometimes the simplest things are hidden in plain sight :) Most people point with their fingers/hands. Unlike rayman, who has vector-like hands, biological beings have them connected to their body, which makes them behave like spinors. But Dirac actually knew about this, after all there is a belt trick named after him.

New comment by aap_ in "Vector Meson Dominance"

aap_ — Fri, 03 Apr 2026 20:36:11 +0000

But with a twist in the arm. After another 360 the arm is back too.

New comment by aap_ in "Vector Meson Dominance"

aap_ — Fri, 03 Apr 2026 20:34:47 +0000

No, around a single axis. if you hold your hand palm up you can rotate in the (vertical) z axis around 360° and get a twist in the arm. another 360° undoes the twist, that's 720° around a single axis.

New comment by aap_ in "Vector Meson Dominance"

aap_ — Fri, 03 Apr 2026 08:29:43 +0000

Very cool! The suggestion to consider how the standard model came to be rather than starting with the result sounds like an excellent idea.

But of course i have to disagree with this: "A spin-1/2 particle is described by a spinor, which is a bit weird, but spin-1 particle is described by something more familiar: a vector!"

In my view a spinor is even more familiar than a vector: it's like a hand - it comes back to itself after 720° of rotation. Just like a vector is like an arrow or a mirror, which come back after 360°. What could be more familiar than a hand?

New comment by aap_ in "Building a Mostly IPv6 Only Home Network"

aap_ — Sun, 29 Mar 2026 17:54:17 +0000

I'd be so much more interested in ipv6 if ISPs would just hand out a stable prefix. as it is ipv6 makes very little sense to me

New comment by aap_ in "I hate: Programming Wayland applications"

aap_ — Sun, 22 Mar 2026 22:24:44 +0000

Because the low level details tend to change over time and then it's too late and you're committed to supporting something that doesn't make sense anymore. like branch delay slots in some RISC cpus, or vulkan (https://www.sebastianaaltonen.com/blog/no-graphics-api)

New comment by aap_ in "I hate: Programming Wayland applications"

aap_ — Sun, 22 Mar 2026 22:16:22 +0000

Interesting that you're saying the BSDs use something sysvinit-based. i never saw any runlevel idea there, which i thought was the primary marker of sysvinit? arch used to have an init system that felt very BSD-like. unfortunately they moved to systemd, and i went to void, but not happy with the init system there either. using linux used to be so much easier when "learning an init system" wasn't really a thing yet.

New comment by aap_ in "Why I love FreeBSD"

aap_ — Mon, 16 Mar 2026 19:31:14 +0000

I was using FreeBSD (after NetBSD) as my primary system for a while in school (no, i can't watch this youtube video, flash doesn't run on FreeBSD). i still use it for my home server, it's just cozy.

New comment by aap_ in "Avoiding Trigonometry (2013)"

aap_ — Thu, 12 Mar 2026 18:38:13 +0000

If you only care about rotations in 3d, quaternions do everything you need :) with all the added benefits of having a division algebra to play with (after all the cross product is a division-algebraic operation). PGA is absolutely great, but quite a bit more complex mathematically, and its spinors are not as obvious as quaternionic ones. in addition GA is commonly taught in a very vector-brained way, but i find spinors much easier to deal with.

New comment by aap_ in "Avoiding Trigonometry (2013)"

aap_ — Thu, 12 Mar 2026 17:10:55 +0000

He's still computing cross(z, d) and dot(z, d) separately. that looks like a code smell to me. with quaternions this would be easier: just calculate the quotient between z and d and take the square root (which means adding 1 and renormalising). the square root is necessary if one is dealing with vectors, which live in a kind of square-y space. finding the rotation between two spinors is even simpler: it's just the quotient of the the spinors as quaternions. unfortunately hamilton's view that quaternions are the quotient of vectors has never been quite abandoned. it's much more natural to think of them as quotients of spinors.

New comment by aap_ in "An interactive version of Byrne's The Elements of Euclid (1847)"

aap_ — Fri, 06 Feb 2026 13:45:19 +0000

This is looking really beautiful! For a long time I've wanted to have a nice edition of the elements in the original greek. There are some pdfs around but they look rather uninspired. Something like Byrne's edition in greek would be so lovely! Though this is not a straight translation but quite reworked to make it more graphical, so probably wouldn't work too well with the original text without some work anyway.

New comment by aap_ in "MIT Whirlwind I: A High-Speed Electronic Digital Computer (1951) [pdf]"

aap_ — Thu, 15 Jan 2026 10:23:42 +0000

Love the Whirlwind! i think of it as the original microcontroller, except not very micro of course. The 2kw address space is a bit small for bigger programs unfortunately, but it's still great fun to play with anyways.

New comment by aap_ in "Understanding the bin, sbin, usr/bin, usr/sbin split (2010)"

aap_ — Sun, 04 Jan 2026 18:36:04 +0000

> This post gets some of the details wrong

"some" is an understatement.

New comment by aap_ in "Understanding the bin, sbin, usr/bin, usr/sbin split (2010)"

aap_ — Sun, 04 Jan 2026 18:11:08 +0000

This is low-effort fantasy history. It may be directionally correct, but why bother when you don't care about the details? From analyzing the UNIX manuals and other old files we get the following (not fully complete) picture:

We'll skip PDP-7 UNIX, no hierarchical file system yet.

UNIX v1 on the PDP-11 had an RF11 fixed head disk (1mb) for / and swap, and an RK05 moving head disk (2.5mb) for /usr (the user directories)

By v2 they had added a second RK05 at /sys for things like the kernel, manual pages, and system language stuff like the c compiler and m6.

By v3 they added yet another RK05 at /crp for, well, all sorts of crap (literally), including yacc apparently. /usr/bin is mentioned here for the first time.

I don't feel like looking up when sbin was first introduced but it is not a Bell Labs thing. possibly BSD or AT&T UNIX? Binaries that one would normally not want to run were kept in /etc, which includes thing like init, mount, umount, getty, but also the second pass of the assembler (as2), or helpers like glob. Also i don't know when /home became canonical but at Bell Labs it was never a thing (plan 9 has user directories in /usr where they had always belonged logically).

The lib situation is more difficult. Looks like it started with /usr/lib. By v3 we find the equivalent directory as /lib, where it contains the two passes of the C compiler (no optimization pass back then), C runtime and lib[abc].a (assembler, B, C libraries respectively). /usr/lib had been repurposed for non-object type libraries, think text-preparation and typesetting.

By v4 the system had escaped the labs (see the recent news) and at that point everyone modified the system to their taste anyway. Perhaps it should be noted that the v7 distribution (which is the first that is very clearly the ancestor of every modern UNIX) has no /usr/bin, only /bin. /lib and /usr/lib are split however.

These are just some rough notes and due to a lack of early material they're still not as accurate as i would like. Also UNIX ran on more than one machine even in the early days (the manuals mention the number of installations) so there must have been some variation anyway. Something I'd like to know in particular is when and where RP03 disk drives were used. These are pretty huge in comparison to the cute RK05s.

New comment by aap_ in "UNIX Fourth Edition"

aap_ — Thu, 01 Jan 2026 14:05:12 +0000

In my experience, yes: always happens. So far i have not found a way to mount multiple disks without getting these inode errors. And this is just v4, the nsys kernel doesn't even work with a single disk. i hope i'll get to the bottom of this in the near future.

New comment by aap_ in "2026: The Year of Java in the Terminal?"

aap_ — Thu, 01 Jan 2026 14:00:35 +0000

Java feels like the COBOL of our times, and the JVM like the IBM 360 architecture.

New comment by aap_ in "UNIX Fourth Edition"

aap_ — Tue, 30 Dec 2025 16:22:34 +0000

That's the puzzling thing. i find it hard to believe they sent out an operating system that can't deal with multiple file systems. yet i can't get them to work correctly. The pre-v4 nsys kernel is another piece in the puzzle. it doesn't have pipes implemented yet but aside from that (i put them in) it also shows these "busy i" bugs, but even when running on a single disk. Maybe there's more i'm doing wrong there since it's running on the fs from the v4 tape. But that i'm getting such similar bugs in different situations suggests there is something wrong that i'm not seeing yet. gotta debug more.

If it turns out to be a timing-related bug it may be that the bug was much less obvious on real hardware.

New comment by aap_ in "UNIX Fourth Edition"

aap_ — Tue, 30 Dec 2025 12:59:08 +0000

Hi, this is me. I'm still hacking on it but ran into some hard to understand kernel bugs. once i mount more than the root filesystem (say /usr/man) there are issues with inode allocation/freeing. mixing and matching v4 and v5 stuff in various ways can also lead to other interesting bugs but often an allocated inode ends up on the freelist, and things break.

Otoh it's so much fun to hack and fiddle with the unix kernel :) very zen