Eta (letter) Updated 2025-07-16
Lowercase looks like a lowercase letter N for some reason.
gothinkster/realworld Updated 2025-07-16
Basically puts together every backend with Front-end web framework to create the exact same website.
The reference live demo can be found at: demo.realworld.io/#/ It is based on Angular.js as it links to: github.com/gothinkster/angularjs-realworld-example-app TODO backend?
There are however also live demos of other frontends, e.g.:
Note that all those frontends communicate with the same backend.
As of 2021 Devs are seemed a bit too focused on monetizing the project through their "how to use this project" premium tutorial, and documentation could be better: just getting the hello world of the most popular backend with the most popular frontend is not easy... come on.
github.com/gothinkster/realworld/issues/578 asks for community support, as devs have moved on since unfortunately.
Remember:
  • by default, the frontends hardcode the upstream public data API: https://conduit.productionready.io/api so you have to hack their code to match the port of the backend. And each backend can have a different port.
  • when you switch between backends, you must first manually clear client-side storage cookies/local new run will fail due to authentication issues!
Important missing things from the minimum base app:
First you should the most popular backend/frontend combination running, which is the most likely to be working. We managed to run on Ubuntu 20.10, React + Node.js Express.js as described at github.com/gothinkster/node-express-realworld-example-app/pull/116:
Then just:
npm install
npm start
on both server and client, and then visit the client URL: localhost:4100/
One cool thing is that the main repo has unified backend API tests:
git clone https://github.com/gothinkster/realworld
cd realworld
git checkout e7adc6b06b459e578d7d4a6738c1c050598ba431
cd api
APIURL=http://localhost:3000/api USERNAME="u$(date +%s)" ./run-api-tests.sh
so the per-repository tests are basically useless, and that single test can test everything for any backend! There is no frontend testing however: github.com/gothinkster/realworld/issues/269 so newb.
Unlike the simple case of a matrix, in infinite dimensional vector spaces, the spectrum may be continuous.
The quintessential example of that is the spectrum of the position operator in quantum mechanics, in which any real number is a possible eigenvalue, since the particle may be found in any position. The associated eigenvectors are the corresponding Dirac delta functions.
Controlled quantum gate Updated 2025-07-16
Controlled quantum gates are gates that have two types of input qubits:
These gates can be understood as doing a certain unitary operation only if the control qubits are enabled or disabled.
The first example to look at is the CNOT gate.
Figure 1. . Source.
The black dot means "control qubit", and "U" means an arbitrary Unitary operation.
When the operand has a conventional symbol, e.g. the Figure "Quantum NOT gate symbol" for the quantum NOT gate to form the CNOT gate, that symbol is used in the operand instead.
There are a few possibilities:
csvtool Updated 2025-07-16
A compiled executable under /usr/bin/csvtool, has an Ubuntu 23.04 package: manpages.ubuntu.com/manpages/lunar/en/man1/csvtool.1.html
There seems to be no sane filtering mechanism however: stackoverflow.com/questions/46540752/using-csvtool-call-to-filter-csv-in-bash
Electronvolt Updated 2025-07-16
After the 2019 redefinition of the SI base units it is by definition exactly Joules.
Looks very impressive! Last update marked 2011 as of 2020.
Goes up to "A.15 quantum field theory in a Nanoshell", Ciro have to review it to see if there's anything worthwhile in that section.
Personal page says he retired as of 2020: www.eng.fsu.edu/~dommelen/ But hopefully he has more time for these notes!
And he appears to have his own lightweight markup language that transpiles to LaTeX called l2h: www.eng.fsu.edu/~dommelen/l2h/
Firmware Updated 2025-07-16
Fujitsu Updated 2025-07-16
The japanese name literally means:
  • 富士 fushi, from Mount Fuji, which itself has unknown origin
  • 通 tong: telecommunications
Positive definite matrix Updated 2025-07-16
The dot product is a positive definite matrix, and so we see that those will have an important link to familiar geometry.
A quote by Ciro's Teacher R.:
Sometimes, even if our end goals are too far from reality, the side effects of trying to reach them can have meaningful impact.
If the goals are not ambitious enough, you risk not even having useful side effects so show in the end!
By doing the prerequisites of the impossible goal you desire, maybe the next generation will be able to achieve it.
This is basically why Ciro Santilli has contributed to Stack Overflow, which has happened while was doing his overly ambitious projects and notice that all kinds of basic pre-requisites were not well explained anywhere.
This is especially effective when you use backward design, because then you will go "down the dependency graph of prerequisites" and smoothen out any particularly inefficient points that you come across.
Going into such productive procrastination is also known informally as yak shaving.
There are of course countless examples of such events:
The danger of this approach is of course spending too much time on stuff that will not be done enough times to be worth it, as highlighted by several xkcds:
Figure 1.
xkcd 974: The general problem
. Source.
Figure 2.
xkcd 1205: Is it worth the time
. Source.

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