Ciro Santilli @cirosantilli 37

 Articles (11k) Discussions (26) Comments (64) Follows  Received likes Files

New Updated  Top  Announced  A-Z  Liked  Followed

Josephson equations Updated 2025-07-16

Two equations derived from first principles by Brian Josephson that characterize the device, somewhat like an I-V curve:

I (t) = I_{c} sin (φ (t)) \frac{d φ ( t )}{d t} = \frac{2 e V ( t )}{ℏ}

where:

$I_{c}$ : Josephson current
$φ$ : the Josephson phase, a function $R \to R$ defined by the second equation plus initial conditions
$V (t)$ : input voltage of the system
$I (t)$ : current across the junction, determined by the input voltage

Note how these equations are not a typical I-V curve, as they are not an instantaneous dependency between voltage and current: the history of the voltage matters! Or in other words, the system has an internal state, represented by the Josephson phase at a given point in time.

To understand them better, it is important to look at some important cases separately:

AC Josephson effect: V is a fixed DC voltage

 Read the full article

Elliptic curve point addition Updated 2025-07-16

Elliptic curve point addition is the group operation of an elliptic curve group, i.e. it is a function that takes two points of an elliptic curve as input, and returns a third point of the elliptic curve as its output, while obeying the group axioms.

The operation is defined e.g. at en.wikipedia.org/w/index.php?title=Elliptic_curve_point_multiplication&oldid=1168754060#Point_operations. For example, consider the most common case for two different points different. If the two points are given in coordinates:

P (x_{p}, y_{p}) + Q + (x_{q}, y_{q}) = R = (x_{r}, y_{r})

then the addition is defined in the general case as:

λ x_{r} y_{r} = \frac{y _{q} - y _{p}}{x _{q} - x _{p}} = λ^{2} - x_{p} - x_{q} = λ (x_{p} - x_{r}) - y_{p}

with some slightly different definitions for point doubling

P + P

and the identity point.

This definition relies only on operations that we know how to do on arbitrary fields:

addition $+$
multiplication $\times$

and it therefore works for elliptic curves defined over any field.

Just remember that:

x / y

x \times y^{- 1}

and that

y^{- 1}

always exists because it is the inverse element, which is guaranteed to exist for multiplication due to the group axioms it obeys.

The group function is usually called elliptic curve point addition, and repeated addition as done for DHKE is called elliptic curve point multiplication.

Figure 1.
Visualisation of elliptic curve point addition
. Source.

 Read the full article

Elon Musk Updated 2025-07-16

Musk is a truly ambivalent personality. Some points are very good. Some are very bad.

Respect on the technical side by Ciro Santilli.

But the way he treated his first wife Justine Musk, is very very weird, incomprehensible: www.marieclaire.com/sex-love/a5380/millionaire-starter-wife/

Positive Cirocoins for possibly going to reverse Twitter's unfair Trump ban if his Twitter acquisition goes through:

twitter.com/elonmusk/status/1519036983137509376
By "free speech", I simply mean that which matches the law.
I am against censorship that goes far beyond the law.
If people want less free speech, they will ask government to pass laws to that effect.
Therefore, going beyond the law is contrary to the will of the people.
twitter.com/elonmusk/status/1507259709224632344

Negative Cirocoins for according to Wikipedia:

Within the merged company [Thiel's Confinity + Elon's X.com], Musk returned as CEO. Musk's preference for Microsoft software over Unix created a rift in the company and caused Thiel to resign.

The REAL Reason Why Tesla Made All Patents Open-Source by The not so boring Man (2021)

Source. Supercut from various interviews/presentations in which Elon saying that Tesla has open source patents and pro open source stuff. Can we trust it? Maybe.

 Read the full article

Engine Updated 2025-07-16

 Read the full article

Enthalpy Updated 2025-07-16

Adds up chemical energy and kinetic energy.

Wikipedia mentions however that the kinetic energy is often negligible, even for gases.

The sum is of interest when thinking about reactions because chemical reactions can change the number of molecules involved, and therefore the pressure.

To predict if a reaction is spontaneous or not, negative enthalpy is not enough, we must also consider entropy via Gibbs free energy.

Bibliography:

chemistry.stackexchange.com/questions/7696/how-do-i-distinguish-between-internal-energy-and-enthalpy

 Read the full article

enwiki-latest-categorylinks.sql Updated 2025-07-16

dumps.wikimedia.org/enwiki/latest/enwiki-latest-categorylinks.sql.gz

The schema is listed at: www.mediawiki.org/wiki/Manual:Categorylinks_table

On the SQL:

CREATE TABLE `categorylinks` (
  `cl_from` int(8) unsigned NOT NULL DEFAULT 0,
  `cl_to` varbinary(255) NOT NULL DEFAULT '',
  `cl_sortkey` varbinary(230) NOT NULL DEFAULT '',
  `cl_timestamp` timestamp NOT NULL DEFAULT current_timestamp() ON UPDATE current_timestamp(),
  `cl_sortkey_prefix` varbinary(255) NOT NULL DEFAULT '',
  `cl_collation` varbinary(32) NOT NULL DEFAULT '',
  `cl_type` enum('page','subcat','file') NOT NULL DEFAULT 'page',
  PRIMARY KEY (`cl_from`,`cl_to`),
  KEY `cl_timestamp` (`cl_to`,`cl_timestamp`),
  KEY `cl_sortkey` (`cl_to`,`cl_type`,`cl_sortkey`,`cl_from`),
  KEY `cl_collation_ext` (`cl_collation`,`cl_to`,`cl_type`,`cl_from`)
) ENGINE=InnoDB DEFAULT CHARSET=binary ROW_FORMAT=COMPRESSED;

TODO what is cl_from? We've tried:

page_id: nope, there is not page_id of 3

cl_to appears to always be a category string name.

The format appears to be described at: www.mediawiki.org/wiki/Manual:Categorylinks_table

A sample INSERT entry is:

(3,'Computer_storage_devices',88,11,0)

 Read the full article

enwiki-latest-category.sql Updated 2025-07-16

dumps.wikimedia.org/enwiki/latest/enwiki-latest-category.sql.gz contains a list of categories. It only contains the categories and some counts, but it doesn't contain the subcategories and pages under each category, so it is a bit pointless.

The schema is listed at: www.mediawiki.org/wiki/Manual:Category_table

The SQL first defines the table:

CREATE TABLE `category` (
  `cat_id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `cat_title` varbinary(255) NOT NULL DEFAULT '',
  `cat_pages` int(11) NOT NULL DEFAULT 0,
  `cat_subcats` int(11) NOT NULL DEFAULT 0,
  `cat_files` int(11) NOT NULL DEFAULT 0,
  PRIMARY KEY (`cat_id`),
  UNIQUE KEY `cat_title` (`cat_title`),
  KEY `cat_pages` (`cat_pages`)
) ENGINE=InnoDB AUTO_INCREMENT=249228235 DEFAULT CHARSET=binary ROW_FORMAT=COMPRESSED;

followed by a few humongous inserts:

INSERT INTO `category` VALUES (2,'Unprintworthy_redirects',1597224,20,0),(3,'Computer_storage_devices',88,11,0)

which we can see at: en.wikipedia.org/wiki/Category:Computer_storage_devices

Se see that en.wikipedia.org/wiki/Category:Computer_storage_devices_by_company

en.wikipedia.org/wiki/Category:Computer_storage_devices is a subcategory of that category and it appears in that file.
en.wikipedia.org/wiki/Acronis_Secure_Zone is a page of the category, and it does not appear

so it contains only categories.

We can check this with:

sed -s 's/),/\n/g' enwiki-latest-category.sql | grep Computer_storage_devices

and it shows:

(3,'Computer_storage_devices',88,11,0
(521773,'Computer_storage_devices_by_company',6,6,0

There doesn't seem to be any interlink between the categories, only page and subcategory counts therefore.

 Read the full article

Epic Rap Battles of History Updated 2025-07-16

www.youtube.com/EpicRapBattles

Most of the videos are crap, but the following ones almost killed Ciro Santilli of laughter:

Video "Bill Gates vs Steve Jobs by Epic Rap Battles of History (2012)"
Video 1. "Rasputin vs Stalin by Epic Rap Battles of History (2013)"

Rasputin vs Stalin by Epic Rap Battles of History (2013)

Source. See also: cirosantilli.com/china-dictatorship/stalin.

Monty Python has a few precursors to the "random famous people mixed together compting" format, although not in the rap fight format:

Communist Quiz by Monty Python (1970)

Source. Has a Wiki page: en.wikipedia.org/wiki/World_Forum/Communist_Quiz. Brings to mind: Video "Football, Football, Football by Mitchell and Webb".

Philosophers' Football Match by Monty Python (1972)

Source. If you can understand the jokes, your philosophy level is pretty good. Like more than zero. Wiki page: en.wikipedia.org/wiki/The_Philosophers%27_Football_Match. Ciro loves how that page currently uses a standard footbal match template to describe the match!

 Read the full article

Equation of state Updated 2025-07-16

 Read the full article

Ethernet cable Updated 2025-07-16

When non-specialists say "Ethernet cable", they usually mean twisted pair for Ethernet over twisted pair.

But of course, this term is much more generic to a more specialized person, since notably fiber optics are also extensively used in Ethernet over fiber.

en.wikipedia.org/wiki/Category:Ethernet_cables

 Read the full article

Euler-Lagrange equation Updated 2025-07-16

Let's start with the one dimensional case. Let the

q : R \to R

and a Functional

I

defined by a function of three variables

F : R^{3} \to R

:

I (q) = \int_{t_{0}}^{t} F (t, q (t), \overset{q}{˙} (t)) d t

Then, the Euler-Lagrange equation gives the maxima and minima of the that type of functional. Note that this type of functional is just one very specific type of functional amongst all possible functionals that one might come up with. However, it turns out to be enough to do most of physics, so we are happy with with it.

Given

F

, the Euler-Lagrange equations are a system of ordinary differential equations constructed from that

F

such that the solutions to that system are the maxima/minima.

In the one dimensional case, the system has a single ordinary differential equation:

\frac{\partial F ( t , q ( t ) , q ˙ ( t ))}{\partial q} - \frac{d}{d t} \frac{\partial F ( t , q ( t ) , q ˙ ( t ))}{\partial q ˙} = 0

By

\frac{\partial F}{\partial q}

and

\frac{\partial F}{\partial q ˙}

we simply mean "the partial derivative of

F

with respect to its second and third arguments". The notation is a bit confusing at first, but that's all it means.

Therefore, that expression ends up being at most a second order ordinary differential equation where

q

is the unknown, since:

the term $\frac{\partial F ( t , q ( t ) , q ˙ ( t ))}{\partial q}$ is a function of $t, q (t), \overset{q}{˙} (t)$
the term $\frac{\partial F ( t , q ( t ) , q ˙ ( t ))}{\partial q ˙}$ is a function of $t, q (t), \overset{q}{˙} (t)$ . And so it's derivative with respect to time will contain only up to $\overset{q}{¨}$

Now let's think about the multi-dimensional case. Instead of having

q : R \to R

, we now have

q : R \to R^{n}

. Think about the Lagrangian mechanics motivation of a double pendulum where for a given time we have two angles.

Let's do the 2-dimensional case then. In that case,

F

is going to be a function of 5 variables

F : R^{5} \to R

rather than 3 as in the one dimensional case, and the functional looks like:

I (q) = \int_{t_{0}}^{t} F (t, q_{1} (t), q_{2} (t), \overset{q_{1}}{˙} (t), \overset{q_{2}}{˙}) (t) d t

This time, the Euler-Lagrange equations are going to be a system of two ordinary differential equations on two unknown functions

q_{1}

and

q_{2}

of order up to 2 in both variables:

\frac{\partial F ( t , q _{1} ( t ) , q _{2} ( t ) , q _{1} ˙ ( t ) , q _{2} ˙ ( t ))}{\partial q _{1}} - \frac{d}{d t} \frac{\partial F ( t , q _{1} ( t ) , q _{2} ( t ) , q _{1} ˙ ( t ) , q _{2} ˙ ( t )}{\partial q _{1} ˙} = 0 \frac{\partial F ( t , q _{1} ( t ) , q _{2} ( t ) , q _{1} ˙ ( t ) , q _{2} ˙ ( t ))}{\partial q _{2}} - \frac{d}{d t} \frac{\partial F ( t , q _{1} ( t ) , q _{2} ( t ) , q _{1} ˙ ( t ) , q _{2} ˙ ( t )}{\partial q _{2} ˙} = 0

At this point, notation is getting a bit clunky, so people will often condense the

q_{i}

vector

\frac{\partial F ( t , q ( t ) , q ˙ ( t ))}{\partial q _{1}} - \frac{d}{d t} \frac{\partial F ( t , q ( t ) , q ˙ ( t ))}{\partial q _{1} ˙} = 0 \frac{\partial F ( t , q ( t ) , q ˙ ( t ))}{\partial q _{2}} - \frac{d}{d t} \frac{\partial F ( t , q ( t ) , q ˙ ( t ))}{\partial q _{2} ˙} = 0

or just omit the arguments of

F

entirely:

\frac{\partial F}{\partial q _{i}} - \frac{d}{d t} \frac{\partial F}{\partial q _{i} ˙} = 0

Calculus of Variations ft. Flammable Maths by vcubingx (2020)

 Read the full article

Europe cookie law Updated 2025-07-16

 Read the full article

Exam as a service Updated 2025-07-16

This is Ciro Santilli's name for the idea that we should not have structured degrees at university that require entry exams, only tests that anybondy could take, likely for free, and then they would just have proof that they know the stuff for e.g. teachers that care about a subject while selecting students to work with them in research.

We just need control rooms where someone can watch students for cheating. Multiple different exams can be taken in the same room of course, students just have to sign up in advance. The exams should happen regularly depending on demand. E.g. extremelly common subjects should happen every month, and highly specialized ones every 6 months or 1 year.

Questions should be always taken from an open question pool which also contains answers, thus allowing anyone to effectively study for it.

How many questions can you actually come up with about a given non research subject, right?

We then make an API available, so that students can grant access to specific results to anyone they choose, or even make the results public for anyone to see. This way the people that care about the exams can just machine learn what exams correlate with their desired performance.

Bibliography:

 Read the full article

Existence of the matrix logarithm Updated 2025-07-16

en.wikipedia.org/wiki/Logarithm_of_a_matrix#Existence mentions it always exists for all invertible complex matrices. But the real condition is more complicated. Notable counter example: -1 cannot be reached by any real

e^{t k}

.

The Lie algebra exponential covering problem can be seen as a generalized version of this problem, because

Lie algebra of $G L (n)$ is just the entire $M_{n}$
we can immediately exclude non-invertible matrices from being the result of the exponential, because $e^{tM}$ has inverse $e^{- tM}$ , so we already know that non-invertible matrices are not reachable

 Read the full article

Existential risk of AGI Updated 2025-07-16

www.cam.ac.uk/research/news/the-best-or-worst-thing-to-happen-to-humanity-stephen-hawking-launches-centre-for-the-future-of

The rise of powerful AI will either be the best or the worst thing ever to happen to humanity. We do not yet know which.

 Read the full article

ExpertRank Updated 2025-07-16

Was adopted by AskJeeves in 2001.

The Google Story Chapter 11. "The Google Economy" comments:

As they saw it, generation one was AltaVista, generation two was Google, and generation three was Teoma, or what Ask Jeeves came to refer to as Expert Rank. Teoma's technology involved mathematical formulas and calculations that went beyond Google's PageRank system, which was based on popularity. In fact, the concept had been cited in the original Stanford University paper written by Sergey Brin and Larry Page as one of the methods that could be used to rank indexed Web sites in response to search requests. "They called their method global popularity and they called this method local popularity, meaning you look more granularly at the Web and see who the authoritative sources are," Lanzone said. He said Brin an Page had concluded that local popularity would be exceedingly difficult to execute well, because either it would require too much processing power to do it in real time or it would take too long.

googlesystem.blogspot.com/2006/03/expertrank-authoritative-search.html mentions

ExpertRank is an evolution of IBM's CLEVER project, a search engine that never made it to public.

and:

The difference between PageRank and ExpertRank is that for ExpertRank the quality of the page is important and that quality is not absolute, but it's relative to a subject.

There are other more recent algorithms with similar names, and are prehaps related:

www.researchgate.net/publication/257015904_ExpertRank_A_topic-aware_expert_finding_algorithm_for_online_knowledge_communities ExpertRank: A topic-aware expert finding algorithm for online knowledge communities (2013)
ieeexplore.ieee.org/document/5260966 ExpertRank: An Expert User Ranking Algorithm in Online Communities

 Read the full article

Fabless manufacturing Updated 2025-07-16

In the past, most computer designers would have their own fabs.

But once designs started getting very complicated, it started to make sense to separate concerns between designers and fabs.

What this means is that design companies would primarily write register transfer level, then use electronic design automation tools to get a final manufacturable chip, and then send that to the fab.

It is in this point of time that TSMC came along, and benefied and helped establish this trend.

The term "Fabless" could in theory refer to other areas of industry besides the semiconductor industry, but it is mostly used in that context.

 Read the full article

Fabrice Bellard Updated 2025-07-16

Creator of QEMU and FFmpeg, both of which Ciro Santilli deeply respects. And a bunch other random stuff.

What is shocking about Fabrice this is that both are insanely important software that Ciro Santilli really likes, and both seem to be completely unrelated subjects!

Google made billions on top of this dude:

FFmpeg is the backend of YouTube
QEMU is the default emulator for Android Studio as of 2019, which Android developers use by default under the hood to develop Android Apps on their desktop without the need for a real device.

At last but not least, Fabrice also studied in the same school that Ciro Santilli studied in France, École Polytechnique.

It is a shame that he keeps such a low profile, there are no videos of him on the web, and he declines interviews.

Another surprising fact is that Fabrice has not worked for the "Big Tech Companies" as far as can be publicly seen, but rather mostly on smaller companies that he co-founded: www.quora.com/Computer-Programmers/Computer-Programmers-Where-is-Fabrice-Bellard-employed

And he's also into some completely random projcts unsurprisingly:

www.computerhistory.org/tdih/january/6/ Computer Scientist Fabrice Bellard Announces Computing Pi to Record Number of Digits

Bibliography:

smartbear.com/de/blog/2011/fabrice-bellard-portrait-of-a-super-productive-pro/ contains a list of his projects as of 2011

Figure 1.
Fabrice Bellard in 2007
. Source. At a restaurant with the author apparently. Plus Miguel De Icaza who was in Paris for some conference, which they all presumably attended.

Figure 2.
Fabrice Bellard with light
. There are no in-focus images of Fabrice on the Internet.

 Read the full article

Fast Fourier transform Updated 2025-07-16

An efficient algorithm to calculate the discrete Fourier transform.

 Read the full article

feathers-chat-react Updated 2025-07-16

github.com/feathersjs-ecosystem/feathers-chat-react

Last updated 2018 as of 2021, but still just worked.

Also uses webpack which is fantastic.

Gotta run github.com/feathersjs/feathers-chat first: github.com/feathersjs-ecosystem/feathers-chat-react/issues/5, then it worked:

git clone https://github.com/feathersjs/feathers-chat
cd feathers-chat
git checkout fd729a47c57f9e6170cc1fa23cee0c84a004feb5
npm install
npm start

and on the other terminal:

git clone https://github.com/feathersjs-ecosystem/feathers-chat-react
cd feathers-chat-react
git checkout 36d56cbe80bbd5596f6a108b1de9db343b33dac3
npm install
npm start

then visit localhost:3000/ and you can create an account and login, tested on Ubuntu 20.10. Data is stored on persistently.

TODO how to merge those two repos into a single repo.

If you disable JavaScript on Chromium, it stops working completely. There is a section on how to solve that at: docs.feathersjs.com/cookbook/express/view-engine.html but it does not cover React specifically. Codaisseur/feathersjs-react-redux-ssr might be good to look into.

 Read the full article

 Unlisted articles are being shown, click here to show only listed articles.