Continuous function Updated +Created
Continuous spectrum (functional analysis) Updated +Created
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 English Updated +Created
Controlled quantum gate Updated +Created
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.
Generic controlled quantum gate symbol
. 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.
Control theory Updated +Created
This basically adds one more ingredient to partial differential equations: a function that we can select.
And then the question becomes: if this function has such and such limitation, can we make the solution of the differential equation have such and such property?
It's quite fun from a mathematics point of view!
Control theory also takes into consideration possible discretization of the domain, which allows using numerical methods to solve partial differential equations, as well as digital, rather than analogue control methods.
Convex polytope Updated +Created
Cool data embedded in the Bitcoin blockchain / ASCII porn Updated +Created
All found so far are also reproduced at: asciiart.website/index.php?art=people/naked%20ladies therefore not blockchain original.
Some of the very first ASCII art present in the blockchain besides BitLen is porn. Surprising?
Cool data embedded in the Bitcoin blockchain / AtomSea & EMBII data format Updated +Created
For a detailed analysis of one transaction see: Nelson-Mandela.jpg.
Best guess so far, all in ASCII hex of output scripts:
How to teach / Help students achieve their goal Updated +Created
Don't set goals for your students.
Ask students what they want to do, and help them achieve that goal.
If they don't know what to do, give suggestions of interesting things they could do.
Once they have a goal, just help them learn everything that is needed to achieve that goal
If they don't have a goal, any attempt to learn is a total and complete waste of time.
This is because the universe of potentially useful things that can be learnt is infinite, and no human can ever learn everything.
The only solution, is to try and learn only what seems necessary to reach your goal, and just try to reach your goal instead.
This approach is called backward design.
"Graduating" and "getting a diploma" are not valid goals, because they are useless. A goal has to be either an amazing specific technological or artistic development.
Cool data embedded in the Bitcoin blockchain / Bibliography Updated +Created
Other Bitcon analysis:
How to teach / Publish somewhere people can comment Updated +Created
Then, if people find errors, or have questions, they will write a comment near the content itself.
Then, next person that comes along and has the same problem, will also find that comment, and your answer will solve their problems too.
The perfect way to do this is to use GitHub issues
How to teach / Publish your material even if it is not perfect Updated +Created
Just make it very clear what you've tried, what you observed, and what you don't understand if anything at all.
This will already open up room for others to come and expand on your attempt, and you are more likely to learn the answers to your questions as they do.
And there's a good chance someone who knows more than you will come along and correct or teach you something new about the subject. For example, this has happened countless times to Ciro Santilli when doing Ciro Santilli's Stack Overflow contributions.
Perfect is the enemy of good.
Examples of famous fails:
How to teach / Text is cheaper than video Updated +Created
Text materials are generally superior to video because they:
  • are faster to create and edit
  • uses less disk space and network bandwidth
  • is easier to search: Ctrl + F on the browser and off you go. And then grep if you have superpowers.
Only produce video material if:
Never create videos of people just speaking hardcore content for long amounts of time.
If you have to use videos, make them as short as possible, and index them with a textual table of contents.
Also consider using sequences of images or GIFs instead of videos, since those are cheaper.
Figure 1.
Textbooks Y U NO HAVE CTRL-F meme
. Source. Same applies to videos.
How to teach / Use English Updated +Created
By writing in English you reach more people.
Writing in any other language is a waste of time.
The reason is simple: English speakers control a huge proportion of the world's GDP.
English is the de-facto Lingua Franca of the second half of the 20th Century, it is the new lingua franca, the new Latin, and there is no escaping it.
Students who don't know English will never do anything truly useful in science and technology. So it is pointless to teach them anything (besides English itself).
How to write technical help requests and bug reports Updated +Created
Ciro Santilli often sees all those genius who are much smarter than him making shitty forum/mailing list posts, they need to learn this:
  • The apparently most important one liner error message must appear in the title, and fuller apparently relevant logs must appear on the body
  • You must always give the version of the software that you are using as either a tag or git SHA
    These are an important part of the minimal working example.
  • For build errors, you must give your OS and compiler version and version of any relevant external library
How to develop Ciro Santilli's website before the OurBigBook migration Updated +Created
The website moved from AsciiDoctor to OurBigBook Markup in 2020, making this section mostly useless. But hey, history!
Ciro's website is powered by GitHub Pages and Jekyll Asciidoc.
Build locally, watch for changes and rebuild automatically, and start a local server with:
git clone --recursive https://github.com/cirosantilli/cirosantilli.github.io
cd cirosantilli.github.io
bundle install
npm install
./run
Source: ./run.
The website will be visible at: localhost:4000.
Tested on the latest Ubuntu.
Publish changes to GitHub Pages:
git add -u
git commit -m 'make yourself look sillier'
./publish
Source: ./publish.
GitHub forces us to use the master branch for the build output... so the actual source is in the branch dev.
Update the gems with:
bundle update
git add Gemfile.lock
git commit -m 'update gems'
His website was originally written in markdown, however those were deprecated in favour of AsciiDoctor when Ciro saw the light, rationale shown at: markdown-style-guideuse-asciidoc
HTML canvas Updated +Created
Allows us to draw with JavaScript pixel by pixel! Great way to create computational physics demos!
Here is an animation demo with some useful controls:
HTML snippet:
new class extends OurbigbookCanvasDemo {
  init() {
    super.init('hello');
    this.pixel_size_input = this.addInputAfterEnable(
      'Pixel size',
      {
        'min': 1,
        'type': 'number',
        'value': 1,
      }
    );
  }
  draw() {
    var pixel_size = parseInt(this.pixel_size_input.value);
    for (var x = 0; x < this.width; x += pixel_size) {
      for (var y = 0; y < this.height; y += pixel_size) {
        var b = ((1.0 + Math.sin(this.time * Math.PI / 16)) / 2.0);
        this.ctx.fillStyle =
          'rgba(' +
          (x / this.width) * 255 + ',' +
          (y / this.height) * 255 + ',' +
          b * 255 +
          ',255)'
        ;
        this.ctx.fillRect(x, y, pixel_size, pixel_size);
      }
    }
  }
}
Human brain Updated +Created
Ciro Santilli feels it is not for his generation though, and that is one of the philosophical things that saddens him the most in this world.
On the other hand, Ciro's playing with the Linux kernel and other complex software which no single human can every fully understand cheer him up a bit. But still, the high level view, that we can have...
Figure 1. Source.
  • 1: Ventriculus lateralis, Cornu frontale
  • 2: Ventriculus lateralis, Pars centralis
  • 3: Calcar avis
  • 4: Ventriculus lateralis, Cornu occipitale
  • 5: Trigonum collaterale
  • 6: Eminentia collateralis
  • 7: Hippocampus
  • 8: Ventriculus lateralis, Cornu temporale
  • 9: Capsula interna
  • 10: Nucleus caudatus
Hyperscale computing Updated +Created
Basically means "company with huge server farms, and which usually rents them out like Amazon AWS or Google Cloud Platform
Figure 1.
Global electricity use by data center type: 2010 vs 2018
. Source. The growth of hyperscaler cloud vs smaller cloud and private deployments was incredible in that period!

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