Not going to lie, this is some cool shit, robot simulation and 3D visualization in the browser.
I like relativistic quantum mechanics.
Best mathematical explanation: Section "Spin comes naturally when adding relativity to quantum mechanics".
Physics from Symmetry by Jakob Schwichtenberg (2015) chapter 3.9 "Elementary particles" has an amazing summary of the preceding chapters the spin value has a relation to the representations of the Lorentz group, which encodes the spacetime symmetry that each particle observes. These symmetries can be characterized by small integer numbers:
- spin 0: representation
- spin half: representation
- spin 1: representationAs usual, we don't know why there aren't elementary particles with other spins, as we could construct them.
Ciro had a small accident in 2021. It wasn't ultra serious, a few cuts, but could have been worse. Here's a post mortem.
Ciro was going to cycle 120 km between two locations he had never cycled before. Ciro had cycled this distance before many many times, so he thought he could do it.
What went wrong:
- on both ends were cities, larger than those Ciro is used to
- on the start, was a port city. You do not want to cycle in port areas, ever! Lots of trucks, narrow side-walks, bad road, danger danger!
- on both sides, endless suburbia. This means you have to check your map every 3 seconds to know which little stree to turn, which is very hard without a way to attach your map to your bike. Ciro had his on his pocket. You lose a lot of time like that!
- there wasn't a lot of sunlight at the time of the year. Not criticial, but still, less than ideal.
- during the ride, part of the "well documented and safe cycle route" was closed off for repairs. It was unclear what the best alternative would be. Ciro went down a path, but it turned to be horrendous countryside, he had to pull his bike over fences
- by then, Ciro was tired and a bit late. He had only eaten sweets all day long. They give you calories, but there's always something missing in them.
- Ciro arrived at the very very large target city, and it was getting dark, and it was rush hour, lots of cars. This was already back on the official bike path, but even those paths are torduous in suburbia
- also, Ciro was meant to meet his wife later, and he was in a rush, worried that she would be worried about him
- at one point, Ciro took the wrong turn for a few hundred meters
- he realized, and turned back
- when coming back, now extra impatient because o the wrong turn, the place he had come from was actually one way street for a very short while until the right turn, so Ciro went against the correct direction...
- a car came. It was relatively slow, because the road was slight uphill for the car, and a turn. The slight downhill also meant Ciro was going a bit faster than he realized
- Ciro tried to go into the sidewalk anyways to make sure he was clear off the car (he was already). When he tried, the wheel stuck, and he flew forward, hitting a wall slightly
This was a perfect example of how many small things add up to an accident.
You have to know when you are tired and hungry and impatient. This is where huge danger lies.
Stop at a shop, eat, sit down. Darkness is not that dangerous if you have lights.
Take a train outside of large cities if needed. Crossing large cities is not something to be taken lightly. You need calm and time to do so safely.
Examples under cmake:
- cmake/hello: just print a message in CMake itself and exit. No compilation.
- cmake/hello_c: C hello world
- cmake/option:
set()andoption()basic examples - cmake/multi_executable
- cmake/multi_file
- cmake/multi_file_recursive
- cmake/shared_lib_external
This would be a dream, but it is also impossible: how can you reconcile automated tasks that are simulated quickly like batch crafting 20 muffings in 30 in-game minutes, with someone who is at the same time fighting a hoard of zombies and taking one action every 2 in-game seconds? Alas.
How to build it: math.stackexchange.com/questions/3137319/how-in-general-does-one-construct-a-cycle-graph-for-a-group/3162746#3162746 good answer with ASCII art. You basically just pick each element, and repeatedly apply it, and remove any path that has a longer version.
Immediately gives the generating set of a group by looking at elements adjacent to the origin, and more generally the order of each element.
TODO uniqueness: can two different groups have the same cycle graph? It does not seem to tell us how every element interact with every other element, only with itself. This is in contrast with the Cayley graph, which more accurately describes group structure (but does not give the order of elements as directly), so feels like it won't be unique.
The author Ole Tange answers every question about it on Stack Exchange. What a legend!
This program makes you respect GNU make a bit more. Good old make with
-j can not only parallelize, but also take in account a dependency graph.Some examples under:
man parallel_exampesTo get the input argument explicitly job number use the magic string sample output:
{}, e.g.:printf 'a\nb\nc\n' | parallel echo '{}'a
b
cTo get the job number use sample output:
{#} as in:printf 'a\nb\nc\n' | parallel echo '{} {#}'a 1
b 2
c 3
c 3{%} contains which thread the job running in, e.g. if we limit it to 2 threads with -j2:printf 'a\nb\nc\nd\n' | parallel -j2 echo '{} {#} {%}'a 1 1
b 2 1
c 3 2
d 4 1% symbol in many programming languages such as C.To pass multiple CLI argments per command you can use sample output:
-X e.g.:printf 'a\nb\nc\nd\n' | parallel -j2 -X echo '{} {#} {%}'a b 1 1
c d 2 2Video "The Biggest Ideas in the Universe | 17. Matter by Sean Carroll (2020)" at youtu.be/dQWn9NzvX4s?t=3707 says that no one has ever been able to come up with an intuitive reason for the proof.
The idea tha taking the limit of the non-classical theories for certain parameters (relativity and quantum mechanics) should lead to the classical theory.
It appears that classical limit is only very strict for relativity. For quantum mechanics it is much more hand-wavy thing. See also: Subtle is the Lord by Abraham Pais (1982) page 55.
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