Suona by Ciro Santilli 35 Updated +Created
One of the most flashy chinese musical instrument!
It is very similar to the Indian shehnai.
Sum of two squares theorem by Ciro Santilli 35 Updated +Created
Superfluid helium-4 by Ciro Santilli 35 Updated +Created
Also sometimes called helium II, in contrast to helium I, which is the non-superfluid liquid helium phase.
Video 1.
Superfluid helium Resonance Experiment by Dietterich Labs (2019)
Source.
Super Mario Bros. reverse engineering by Ciro Santilli 35 Updated +Created
Commented and labelled disassembly: gist.github.com/1wErt3r/4048722
Decompilation project: github.com/MitchellSternke/SuperMarioBros-C. That project does not produce the ROM however, it reimplements an emulator + game in a single binary.
Video 1.
Small Fire Mario glitch by Kosmic (2022)
Source.
Video 2.
Beating Super Mario Bros. as SLOWLY as Possible by Kosmic (2020)
Source.
Sutta Piṭaka by Ciro Santilli 35 Updated +Created
Sylvester's law of inertia by Ciro Santilli 35 Updated +Created
The theorem states that the number of 0, 1 and -1 in the metric signature is the same for two symmetric matrices that are congruent matrices.
For example, consider:
The eigenvalues of are and , and the associated eigenvectors are:
symPy code:
A = Matrix([[2, sqrt(2)], [sqrt(2), 3]])
A.eigenvects()
and from the eigendecomposition of a real symmetric matrix we know that:
Now, instead of , we could use , where is an arbitrary diagonal matrix of type:
With this, would reach a new matrix :
Therefore, with this congruence, we are able to multiply the eigenvalues of by any positive number and . Since we are multiplying by two arbitrary positive numbers, we cannot change the signs of the original eigenvalues, and so the metric signature is maintained, but respecting that any value can be reached.
Note that the matrix congruence relation looks a bit like the eigendecomposition of a matrix:
but note that does not have to contain eigenvalues, unlike the eigendecomposition of a matrix. This is because here is not fixed to having eigenvectors in its columns.
But because the matrix is symmetric however, we could always choose to actually diagonalize as mentioned at eigendecomposition of a real symmetric matrix. Therefore, the metric signature can be seen directly from eigenvalues.
Also, because is a diagonal matrix, and thus symmetric, it must be that:
What this does represent, is a general change of basis that maintains the matrix a symmetric matrix.
SVG 1.2 by Ciro Santilli 35 Updated +Created
Dropped in favor of SVG 2.
Systems programmer by Ciro Santilli 35 Updated +Created
Computer manufacturer by Ciro Santilli 35 Updated +Created
This section is about companies that integrate parts and software from various other companies to make up fully working computer systems.
Taylor series by Ciro Santilli 35 Updated +Created
Tax the rich by Ciro Santilli 35 Updated +Created
Video 1.
How the rich avoid paying taxes by Vox (2021)
Source. Features interview with Morris Pearl, a rich dude that is campaigning to tax the rich. He also participates in an association called "Patriotic Millionaires" to further this agenda.
Video 2.
What Eating the Rich Did For Japan by Asianometry (2021)
Source.
Seymour Cray by Ciro Santilli 35 Updated +Created
Telephone-based system by Ciro Santilli 35 Updated +Created
This section is about telecommunication systems that are based on top of telephone lines.
Telephone lines were ubiquitous from early on, and many technologies used them to send data, including much after regular phone calls became obsolete with VoIP.
These market forces tended to eventually crush non-telephone-based systems such as telex. Maybe in that case it was just that the name sounded like a thing of the 50's. But still. Dead.
Video 1.
Long Distance by AT&T (1941)
Source. youtu.be/aRvFA1uqzVQ?t=219 is perhaps the best moment, which attempts to correlate the exploration of the United States with the founding of the U.S. states.
Text-based game by Ciro Santilli 35 Updated +Created
Although Ciro Santilli is a big fan of plaintext files and of Vim, not so for games. Games must be easy to understand since they are just a toy.
Tilesets to the rescue!
Text-to-video by Ciro Santilli 35 Updated +Created
This was the Holy Grail as of 2023, when text-to-image started to really take off, but text-to-video was miles behind.
The best television series by Ciro Santilli 35 Updated +Created
The BBC 1979-1982 adaptations of John Le Carré's novels are the best miniseries ever made:They are the most realistic depiction of spycraft ever made.
Some honorable mentions:
You just map the value (1, 1) to the value 1 of , and it works out. E.g. for , the group generated by of (1, 1) is:
0 = (0, 0)
1 = (1, 1)
2 = (0, 2)
3 = (1, 0)
4 = (0, 1)
5 = (1, 2)
6 = (0, 0) = 0
Pinned article: ourbigbook/introduction-to-the-ourbigbook-project
Welcome to the OurBigBook Project! Our goal is to create the perfect publishing platform for STEM subjects, and get university-level students to write the best free STEM tutorials ever.
Everyone is welcome to create an account and play with the site: ourbigbook.com/go/register. We belive that students themselves can write amazing tutorials, but teachers are welcome too. You can write about anything you want, it doesn't have to be STEM or even educational. Silly test content is very welcome and you won't be penalized in any way. Just keep it legal!
Video 1.
Intro to OurBigBook
. Source.
We have two killer features:
  1. topics: topics group articles by different users with the same title, e.g. here is the topic for the "Fundamental Theorem of Calculus" ourbigbook.com/go/topic/fundamental-theorem-of-calculus
    Articles of different users are sorted by upvote within each article page. This feature is a bit like:
    • a Wikipedia where each user can have their own version of each article
    • a Q&A website like Stack Overflow, where multiple people can give their views on a given topic, and the best ones are sorted by upvote. Except you don't need to wait for someone to ask first, and any topic goes, no matter how narrow or broad
    This feature makes it possible for readers to find better explanations of any topic created by other writers. And it allows writers to create an explanation in a place that readers might actually find it.
    Figure 1.
    Screenshot of the "Derivative" topic page
    . View it live at: ourbigbook.com/go/topic/derivative
    Video 2.
    OurBigBook Web topics demo
    . Source.
  2. local editing: you can store all your personal knowledge base content locally in a plaintext markup format that can be edited locally and published either:
    • to OurBigBook.com to get awesome multi-user features like topics and likes
    • as HTML files to a static website, which you can host yourself for free on many external providers like GitHub Pages, and remain in full control
    This way you can be sure that even if OurBigBook.com were to go down one day (which we have no plans to do as it is quite cheap to host!), your content will still be perfectly readable as a static site.
    Figure 5. . You can also edit articles on the Web editor without installing anything locally.
    Video 3.
    Edit locally and publish demo
    . Source. This shows editing OurBigBook Markup and publishing it using the Visual Studio Code extension.
    Video 4.
    OurBigBook Visual Studio Code extension editing and navigation demo
    . Source.
  3. https://raw.githubusercontent.com/ourbigbook/ourbigbook-media/master/feature/x/hilbert-space-arrow.png
  4. Infinitely deep tables of contents:
    Figure 6.
    Dynamic article tree with infinitely deep table of contents
    .
    Descendant pages can also show up as toplevel e.g.: ourbigbook.com/cirosantilli/chordate-subclade
All our software is open source and hosted at: github.com/ourbigbook/ourbigbook
Further documentation can be found at: docs.ourbigbook.com
Feel free to reach our to us for any help or suggestions: docs.ourbigbook.com/#contact