Ah, you're right. "30 verses" made it sound like more than what you can see on that image. Luckily most of the papyrus is very legible! even if fragmented...
So is there any way to actually read it? Or do i have to buy an obscure french book? can you even buy the book?
Academic publishing/gatekeeping is such a joke.
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.
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.
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.
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?
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)
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.
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.
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.
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.
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.
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.
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.