E.g. a Galilean transformation generally changes the exact values of coordinates, but not the form of the laws of physics themselves.
Lorentz covariance is the main context under which the word "covariant" appears, because we really don't want the form of the equations to change under Lorentz transforms, and "covariance" is often used as a synonym of "Lorentz covariance".
TODO some sources distinguish "invariant" from "covariant": invariant vs covariant.
See also: covariance.
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convert -size 256x256 radial-gradient:white-black out.png- drive.google.com/file/d/1JTPVd09NPaGH-KzGv2jU3XXcFiJAoUjw/view some crazy due investigating, let's see how long until it goes down, posted at: Points to:"Alex Conferno" is also brought up: twitter.com/conferno
- www.reddit.com/r/DataHoarder/comments/12trawt/has_anyone_ever_actually_spoken_to_denis_petrov/
- gyrovague.com/2023/08/05/archive-today-on-the-trail-of-the-mysterious-guerrilla-archivist-of-the-internet/. Trended on Hacker News: news.ycombinator.com/item?id=37009598
- gigazine.net/gsc_news/en/20240326-archive-today/
Other mentions of "Denis Petrov":
The first diodes. These were apparently incredibly unreliable, especially for portable radios, as you had to randomly search for the best contact point you could find in a random polycrystalline material!!
And also quality was highly dependant on where the material was sourced from as that affected the impurities present in the material. Later this was understood to be an issue of doping.
It was so unreliable that vacuum tube diodes overtook them in many applications, even though crystal detectors are actually semiconductor diodes, which eventually won over!
For a long time, before artificial semiconductors kicked in, people just didn't know the underlying physical working principle of these detectors. What I cannot create, I do not understand basically.
From Raw Crystal to Crystal oscillator
. Source. by United States Army Signal Corps (1943)The generic tool recommendation question: unix.stackexchange.com/questions/7425/is-there-a-robust-command-line-tool-for-processing-csv-files
Simple example:output:
printf '00,11,22\n33,44,55\n' | csvgrep -H -c2 -r '^11$' | tail -n+200,11,22Lots of features, but slow because written in Python. A faster version may be csvtools. Also some annoyances like obtuse header handing and missing features like grep + cut in one go: csvgrep and select column in csvkit.
Build failed with
undefined reference to pcre_config on Ubuntu 23.04: github.com/DavyLandman/csvtools/issues/18Unfortunately it is lacking some basic options, like optional header + selecting column by index on
csvgrep (though csvcut has it). The project seems kind of dead.Also unclear if it allows to filter + print only selected columns.
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