DNA Updated 2025-07-16
Since DNA is the centerpiece of life, Ciro Santilli is extremely excited about DNA-related technologies, see also: molecular biology technologies.
Hexagon Updated 2025-07-16
Matrix multiplication Updated 2025-07-16
Since a matrix can be seen as a linear map , the product of two matrices can be seen as the composition of two linear maps:
One cool thing about linear functions is that we can easily pre-calculate this product only once to obtain a new matrix, and so we don't have to do both multiplications separately each time.
Quaternion Updated 2025-07-16
Kind of extends the complex numbers.
Some facts that make them stand out:
Baker-Campbell-Hausdorff formula Updated 2025-07-16
Solution for given and of:
where is the exponential map.
If we consider just real number, , but when X and Y are non-commutative, things are not so simple.
Furthermore, TODO confirm it is possible that a solution does not exist at all if and aren't sufficiently small.
This formula is likely the basis for the Lie group-Lie algebra correspondence. With it, we express the actual group operation in terms of the Lie algebra operations.
Notably, remember that a algebra over a field is just a vector space with one extra product operation defined.
Since a group is basically defined by what the group operation does to two arbitrary elements, once we have that defined via the Baker-Campbell-Hausdorff formula, we are basically done defining the group in terms of the algebra.
Barn (unit) Updated 2025-07-16
Battle of Algiers (1966) Updated 2025-07-16
There's nothing like seeing the hypocrisy of the "Liberté, Égalité, Fraternité" people destroyed.
Interesting how Algeria now supports China's Xinjiang policy in 2019. But of course, dictatorships tend to work together
Ciro Santilli's father, an avid history reader, and in particular interested in the military dictatorship in Brazil through which he lived, once told Ciro how the French torture doctrine was directly adopted by Brazillian military, e.g. then even invited general Paul Aussaresses who had served in Algeria, to help them out with intelligence operations and give courses. Bro, fuck that.
Potassium Updated 2025-07-16
BB84 Updated 2025-07-16
Does not require entangled particles, unlike E91 which does.
en.wikipedia.org/w/index.php?title=Quantum_key_distribution&oldid=1079513227#BB84_protocol:_Charles_H._Bennett_and_Gilles_Brassard_(1984) explains it well. Basically:
  • Alice and Bob randomly select a measurement basis of either 90 degrees and 45 degrees for each photon
  • Alice measures each photon. There are two possible results to either measurement basis: parallel or perpendicular, representing values 0 or 1. TODO understand better: weren't the possible results supposed to be pass or non-pass? She writes down the results, and sends the (now collapsed) photons forward to Bob.
  • Bob measures the photons and writes down the results
  • Alice and Bob communicate to one another their randomly chosen measurement bases over the unencrypted classic channel.
    This channel must be authenticated to prevent man-in-the-middle. The only way to do this authentication that makes sense is to use a pre-shared key to create message authentication codes. Using public-key cryptography for a digital signature would be pointless, since the only advantage of QKD is to avoid using public-key cryptography in the first place.
  • they drop all photons for which they picked different basis. The measurements of those which were in the same basis are the key. Because they are in the same basis, their results must always be the same in an ideal system.
  • if there is an eavesdropper on the line, the results of measurements on the same basis can differ.
    Unfortunately, this can also happen due to imperfections in the system.
    Alice and Bob must decide what level of error is above the system's imperfections and implies that an attacker is listening.
Bell's theorem Updated 2025-07-16
Basically a precise statement of "quantum entanglement is spooky".
Biconvex spherical lens Updated 2025-07-16
Each side is a sphere section. They don't have to have the same radius, they are still simple to understand with different radiuses.
The two things you have to have in mind that this does are:
Big O notation Updated 2025-07-16
Module bound above, possibly multiplied by a constant:
is defined as:
E.g.:
  • . For , is enough. Otherwise, any will do, the bottom line will always catch up to the top one eventually.
Bijection Updated 2025-07-16
Football Updated 2025-07-16
Football is a synonym for association football, can we be done with that! The word "soccer" is an aberration.

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