Genius: Richard Feynman and Modern Physics by James Gleick (1994) Updated +Created
This is a good book.
It has some overlap with Surely You're Joking, Mr. Feynman, which it likely takes as primary sources of some stories.
However, while Surely goes into a lot of detail of each event, this book paints a more cohesive and global picture of things.
In terms of hard physics/mathematics, this book takes the approach of spending a few paragraphs in some chapters describing in high level terms some of the key ideas, which is a good compromise. It does sometime fall into the sin of to talk about something without giving the real name to not scare off the audience, but it does give a lot of names, notably it talks a lot about Lagrangian mechanics. And it goes into more details than Surely in any case.
Geographical division of England Updated +Created
Lebesgue integral of is complete but Riemann isn't Updated +Created
And then this is why quantum mechanics basically lives in : not being complete makes no sense physically, it would mean that you can get closer and closer to states that don't exist!
qflow Updated +Created
They apparently even produced a real working small RISC-V chip with the flow, not bad.
Why can't you collimate incoherent light as well as a laser? Updated +Created
You could put an LED in a cavity with a thin long hole but then, most rays, which are not aligned with the hole, will just bounce inside forever producing heat.
So you would have a very hot device, and very little efficiency on the light output. This heat might also behave like a black-body radiation source, so you would not have a single frequency.
The beauty of lasers is the laser cavity (two parallel mirrors around the medium) selects parallel motion preferentially, see e.g.: youtu.be/_JOchLyNO_w?t=832 from Video "How Lasers Work by Scientized (2017)"
Ciro Santilli's bicycle wisdom Updated +Created
Sometimes, these are more than just mechanics, but also have deeper life analogues. The title of Zen and the Art of Motorcycle Maintenance comes to mind. Sometimes they are just mechanics.
With more philosophical metaphors:
  • when your bike breaks, that provides an unique opportunity to learn how to fix it: try to fix your own bike before taking it to the shop
  • if the wind is blowing against you on the way out, it will likely blow behind you on the way back. But remember that the other way around also applies.
  • always take one extra clothing layer than what you think you will need in your back pocket or sport bag, especially when time is changing fast in Sprint and Autumn. The weather on the road outside of town can change very quickly!
  • if you took a turn, and it feels wrong, stop to check the map, and possibly backtrack to safety. When it feels wrong, it usually is a bad idea, e.g. roads where cars are too fast/too many. But if you take a wrong turn and it feels right, then follow it without fear and see what it leads to!
  • don't carry a speedometer on your bike. Analysis can be done afterwards on Strava. The only measurement that matters is "how awesome am I feeling right now?". Live in the moment instead of checking your speedometer every 10 seconds.
  • cycle when you body calls it out of addiction, not out a goal that you've made up that must be reached
With less philosophical metaphors:
  • learn how much water and food you need to take for a trip. Otherwise, you will bonk at some time, when you least expect, it happens very suddenly.
    And then you better hope to God that you can find a food shop nearby. Luckily this was the case for Ciro's first and only bonk so far.
    And besides bonking all out, being tired and hungry makes you make stupid decision, especially where traffic is involved!
    Food is safety. Light is safety. Time is safety. Calm is safety. Chocolate bars and candy cannot count as lunch food, only delay lunch. A sandwich with ham cheese and salad is food. A bag of M&M's with a can of soda can bring you back from the dead.
    When you are not in familiar grounds, take twice as much as you think you might possibly ever need. Hofstadter's law.
    You will also learn that, surprise surprise, carbohydrates that you ate one or two days before a ride stay stored in your liver and muscles, and also greatly affect how quickly you will bonk, thus the concept of carbohydrate loading.
    Video 1.
    How Not To 'Hit The Wall' Or 'Bonk' – GCN's Guide To Fuelling While Cycling by Global Cycling Network (2016)
    Source.
    And surprise surprise: heat can also make you bonk! Who would have thought!
  • correct saddle hight is fundamental, your legs must be almost fully stretched at the bottom position
  • it is impossible to reach the correct tire pressure with (cheap?) hand pumps, their only purpose is to fill up a flat tire so you can get home after a long ride. But a track pump.
  • clean and lube your chain. The speed benefit is instantaneous and mind blowing. It also greatly improves gear shifting.
    This also prevents the chain from rusting, because the lube takes up the place where water would stay, and the muck makes it harder for water to evaporate.
    This is the most common bike maintenance mistake you see on the streets: people with that high pitched overly dry chain noise.
    Video 2.
    How To Get A Perfectly Clean Chain by GCN (2016)
    Source.
  • when a piece on your bike breaks and has no clear name written on it, you can try to identify it Google images
  • the more you watch YouTube maintenance videos without haste, the more you end up learn random new stuff that unexpectedly saves you later
  • if you took a turn, and it feels wrong, stop to check the map, and possibly backtrack to safety. When it feels wrong, it usually is a bad idea, e.g. roads where cars are too fast/too many
  • public place with lots of people are bicycle parking Hell, because due to anonymity and the large number of distractions, it becomes exponentially more likely that someone will fuck you bike somehow, e.g. by dropping it on the ground. Always search a bit for a reasonable place to park, and avoid overcrowded parking spaces at all costs.
  • gear change matters
    • when you get on your bike to start riding, start riding slowly and gradually switch up pedal forces and gears. Things may have shifted in a weird position as it gets kicked around in parking. Ciro managed to bend his derailleur like that!
    • spin to win, AKA learn to user your gears
    • it is not shameful to ride on your lower gears on a hill. You can actually go surprisingly fast with them, and conserve energy for later. Learn when to use each gear ratio.
  • learn to identify your suppliers:
  • always take your lights off the bike into your bag when you park, anywhere, and for any amount of time, even if a quick stop. Drug addicts are everywhere, always ready love to steal and resell them.
  • sometimes you do something stupid like going into a really muddy path, and it is really fun, because you've never been there in your life. But then your bike gets really dirty, and your feet are wet and freezing, and you promise yourself you will never do something that stupid again. But then you do it again in a different location, because it was too much fun. Once more unto the breach just comes to Ciro's mind every such time. Embrace this.
CPLEX Updated +Created
GF(4) Updated +Created
Ciro Santilli tried to add this example to Wikipedia, but it was reverted, so here we are, see also: Section "Deletionism on Wikipedia".
This is a good first example of a field of a finite field of non-prime order, this one is a prime power order instead.
, so one way to represent the elements of the field will be the to use the 4 polynomials of degree 1 over GF(2):
  • 0X + 0
  • 0X + 1
  • 1X + 0
  • 1X + 1
Note that we refer in this definition to anther field, but that is fine, because we only refer to fields of prime order such as GF(2), because we are dealing with prime powers only. And we have already defined fields of prime order easily previously with modular arithmetic.
Over GF(2), there is only one irreducible polynomial of degree 2:
Addition is defined element-wise with modular arithmetic modulo 2 as defined over GF(2), e.g.:
Multiplication is done modulo , which ensures that the result is also of degree 1.
For example first we do a regular multiplication:
Without modulo, that would not be one of the elements of the field anymore due to the !
So we take the modulo, we note that:
and by the definition of modulo:
which is the final result of the multiplication.
TODO show how taking a reducible polynomial for modulo fails. Presumably it is for a similar reason to why things fail for the prime case.
GHDL Updated +Created
Examples under vhdl.
First install GHDL. On Ubuntu:
sudo apt install verilator
Tested on Verilator 1.0.0, Ubuntu 22.04.
Run all examples, which have assertions in them:
cd vhdl
./run
Khronos Group Updated +Created
The fact that they kept the standard open source makes them huge heroes, see also: closed standard.
Shame that many (most?) of their proposals just die out.
Odd permutation Updated +Created
Ordered tree Updated +Created
Gilberto Gil Updated +Created
Gilberto is definitely the most psychedelic/tribal one of the The Holy Trinity of popular Brazilian music, though he also has a boyish quality to his soul.
He is also perhaps the one that impresses Ciro Santilli the most, at times he can't help but feel:
OMG how the hell did he come up with that?!
Figure 2.
Gilberto Gil in the cover of his 1977 album Refavela
. Source.
GitHub's replacement of master branch with main (2020) Updated +Created
By GitHub around Black Lives Matter, due to a possible ludicrous relationship with slavery of black people:For the love of God, the word "master" is much more general than black slavery. If you are going to ban it, you might as well ban the word "evil".
Several software projects followed the purge from their codebases, maybe GitHub followed someone else's lead, it's hard to say.
The words "whitelist" and "blacklist" were also targeted.
git mergetool with meld or kdiff3 Updated +Created
These are good free newbie GUI options:
sudo apt install meld
git mergetool --tool meld

sudo apt install kdiff3
git mergetool --tool kdiff3
https://raw.githubusercontent.com/cirosantilli/media/master/meld.png
https://raw.githubusercontent.com/cirosantilli/media/master/kdiff3.png
Let's make a more interesting conflict:
git-tips-2.sh
#!/usr/bin/env bash

set -eux

add() (
  rm -f f
  for i in `seq 10`; do
    printf "before $i\n\n" >> f
  done
  printf "conflict 1 $1\n\n" >> f
  for i in `seq 10`; do
    printf "middle $i\n\n" >> f
  done
  printf "conflict 2 $2\n\n" >> f
  for i in `seq 10`; do
    printf "after $i\n\n" >> f
  done
  git add f
)

rm -rf git-tips-2
mkdir git-tips-2
cd git-tips-2
git init

for i in 1 2 3; do
  add $i $i
  git commit -m $i
done

add 3 4
git commit -m 4

add 5 4
git commit -m 5

git checkout HEAD~2
git checkout -b my-feature

add 3 6
git commit -m 6

add 7 6
git commit -m 7
HAVING (SQL) Updated +Created
Pipeline stall Updated +Created
Sycamore processor Updated +Created
This is a good read: quantumai.google/hardware/datasheet/weber.pdf May 14, 2021. Their topology is so weird, not just a rectangle, one wonders why! You get different error rates in different qubits, it's mad.
Figure 1.
Google Sycamore Weber quantum computer connectivity graph
. Weber is a specific processor of the Sycamore family. From this we see it clearly that qubits are connected to at most 4 other qubits, and that the full topology is not just a simple rectangle.
WebRISC-V Updated +Created

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