Convolutional neural network Updated 2025-07-16
YouTube channels that just go over Stack Exchange questions Updated 2025-07-16
Some people have been creating YouTube channels that just post and go over a large number of Stack Exchange questions, some of them with a quick random intro video. Perfectly legal due to CC BY-SA but really weird stuff!
- Roel Van de Paar www.youtube.com/@RoelVandePaar. This one seems to be the OG. As of June 2024 it had 2M videos (!), 161K subscribers and only 47M views. youtube.fandom.com/wiki/Roel_Van_de_Paar mentions "he has the highest number of uploads of any YouTube channel". Interestingly at www.linkedin.com/in/roelvandepaar/?originalSubdomain=au he says he is a test engineer at MariaDB.
- Peter Schneider www.youtube.com/@peterschneiderQandA e.g. www.youtube.com/watch?v=GBQhrKRpUdI "How to put a newline special character into a file using the echo command and redirection operator?" from unix.stackexchange.com/questions/191694/how-to-put-a-newline-special-character-into-a-file-using-the-echo-command-and-re)Stackexchange
- Sophia Wagner www.youtube.com/@SophiaWagnerQandA. As of June 2024 it had 14k videos and only 88k views, so she made 88 bucks on it.
- E.g. www.youtube.com/watch?v=elIlkJneVBI "Vertically stack multiple images using ImageMagick" goes over superuser.com/questions/290656/vertically-stack-multiple-images-using-imagemagick
- www.youtube.com/@LukeChaffeyTechInfo Luke Chaffey, an Indian-American dude, e.g. www.youtube.com/watch?v=wmx6mN_G83s "Do Boost Geometry nearest queries always sort results ordered by smallest distance first?"
- www.youtube.com/@pythonoracle The Python Oracle. Speech synthesis, with different accents. Cute!
Adenine nucleotide translocator Updated 2025-07-16
Adenosine triphosphate Updated 2025-07-16
CC BY Updated 2025-07-16
Polarity symbols Updated 2025-07-16
Political correctness Updated 2025-07-16
Ciro Santilli believes it generally hurts more than it helps.
Especially when you can't even mention censored things to criticize them. You have to pretend they never existed. So people will forget about them, and do them again in the future.
Coprime Updated 2025-07-16
Point particle Updated 2025-07-16
This idealization does not seems to be possible at all in the context of Maxwell's equations with pointlike particles.
Taylor expansion definition of the exponential function Updated 2025-07-16
The Taylor series expansion is the most direct definition of the expontial as it obviously satisfies the exponential function differential equation:
Adjoint operator Updated 2025-07-16
Given a linear operator over a space that has a inner product defined, we define the adjoint operator (the symbol is called "dagger") as the unique operator that satisfies:
Adolfo Amidei Updated 2025-07-16
This dude mentored Enrico Fermi in high school. Ciro Santilli added some info to Fermi's Wikipedia page at: en.wikipedia.org/w/index.php?title=Enrico_Fermi&type=revision&diff=1050919447&oldid=1049187703 from Enrico Fermi: physicist by Emilio Segrè (1970):
In 1914, Fermi, who used to often meet with his father in front of the office after work, met a colleague of his father called Adolfo Amidei, who would walk part of the way home with Alberto [Enrico's father]. Enrico had learned that Adolfo was interested in mathematics and physics and took the opportunity to ask Adolfo a question about geometry. Adolfo understood that the young Fermi was referring to projective geometry and then proceeded to give him a book on the subject written by Theodor Reye. Two months later, Fermi returned the book, having solved all the problems proposed at the end of the book, some of which Adolfo considered difficult. Upon verifying this, Adolfo felt that Fermi was "a prodigy, at least with respect to geometry", and further mentored the boy, providing him with more books on physics and mathematics. Adolfo noted that Fermi had a very good memory and thus could return the books after having read them because he could remember their content very well.
Ciro Santilli really likes guys like this. Given that he does not have the right genetics, conditions and temperance for scientific greatness in this lifetime, he dreams of one day finding his own Fermi instead.
Polynomial over a ring Updated 2025-07-16
However, there is nothing in the immediate definition that prevents us from having a ring instead, i.e. a field but without the commutative property and inverse elements.
The only thing is that then we would need to differentiate between different orderings of the terms of multivariate polynomial, e.g. the following would all be potentially different terms:while for a field they would all go into a single term:so when considering a polynomial over a ring we end up with a lot more more possible terms.
If the ring is a commutative ring however, polynomials do look like proper polynomials: Section "Polynomial over a commutative ring".
Position and momentum space Updated 2025-07-16
One of the main reasons why physicists are obsessed by this topic is that position and momentum are mapped to the phase space coordinates of Hamiltonian mechanics, which appear in the matrix mechanics formulation of quantum mechanics, which offers insight into the theory, particularly when generalizing to relativistic quantum mechanics.
One way to think is: what is the definition of space space? It is a way to write the wave function such that:And then, what is the definition of momentum space? It is of course a way to write the wave function such that:
- the position operator is the multiplication by
- the momentum operator is the derivative by
- the momentum operator is the multiplication by
physics.stackexchange.com/questions/39442/intuitive-explanation-of-why-momentum-is-the-fourier-transform-variable-of-posit/39508#39508 gives the best idea intuitive idea: the Fourier transform writes a function as a (continuous) sum of plane waves, and each plane wave has a fixed momentum.
Bibliography:
PostgreSQL Updated 2025-07-16
PostgreSQL feels good.
Its feature set is insanely large! Just look at stuff like: stackoverflow.com/questions/1986491/sql-split-string-by-space-into-table-in-postgresql/1993058#1993058
If Oracle is the Microsoft of database, Postgres is the Linux, and MySQL (or more precisely MariaDB) is the FreeBSD (i.e. the one that got delayed by legal issues). Except that their software licenses were accidentally swapped.
The only problem with Postgres is its name. PostgreSQL is so unpronounceable and so untypeable that you should just call it "Postgres" like everyone else.
German learned society Updated 2025-07-16
Helium Updated 2025-07-16
PostgreSQL logging Updated 2025-07-16
Ubuntu 21.10 has a certain default level of logging by default to:but it does not log everything, only/mostly errors it seems.
/var/log/postgresql/postgresql-13-main.log
Setting:under:and then restarting the server:just works.
log_statement = 'all'
/etc/postgresql/13/main/postgresql.conf
sudo service restart postgresql
Realtime monitoring for long queries instead: stackoverflow.com/questions/8597516/app-to-monitor-postgresql-queries-in-real-time
Power, performance and area Updated 2025-07-16
This is the mantra of the semiconductor industry:
- power and area are the main limiting factors of chips, i.e., your budget:
- chip area is ultra expensive because there are sporadic errors in the fabrication process, and each error in any part of the chip can potentially break the entire chip. Although there areThe percentage of working chips is called the yield.In some cases however, e.g. if the error only affects single CPU of a multi-core CPU, then they actually deactivate the broken CPU after testing, and sell the worse CPU cheaper with a clear branding of that: this is called binning www.tomshardware.com/uk/reviews/glossary-binning-definition,5892.html
- power is a major semiconductor limit as of 2010's and onwards. If everything turns on at once, the chip would burn. Designs have to account for that.
- performance is the goal.Conceptually, this is basically a set of algorithms that you want your hardware to solve, each one with a respective weight of importance.Serial performance is fundamentally limited by the longest path that electrons have to travel in a given clock cycle.The way to work around it is to create pipelines, splitting up single operations into multiple smaller operations, and storing intermediate results in memories.
Representation of the Lorentz group Updated 2025-07-16
One of the representations of the Lorentz group that show up in the Representation theory of the Lorentz group.
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