Ciro Santilli @cirosantilli 37

Magic software that allows you to write a single program that runs on a wide range of hardware.

Change sign if you swap two input values.

Multivariate polynomial where each term has degree 2, e.g.:is a quadratic form because each term has degree 2:but e.g.:is not because the term $x^3$ has degree 3.

More generally for any number of variables it can be written as:

There is a 1-to-1 relationship between quadratic forms and symmetric bilinear forms. In matrix representation, this can be written as:where $\vec{x}$ contains each of the variabes of the form, e.g. for 2 variables:

Strictly speaking, the associated bilinear form would not need to be a symmetric bilinear form, at least for the real numbers or complex numbers which are commutative. E.g.:But that same matrix could also be written in symmetric form as:so why not I guess, its simpler/more restricted.

Upside: superconducting above 92K, which is above the 77K of liquid nitrogen, and therefore much much cheaper to obtain and maintain than liquid helium.

Downside: it is brittle, so how do you make wires out of it? Still, can already be used in certain circuits, e.g. high temperature SQUID devices.

This single experimental observation/idea is the basis for all of special relativity.

Special relativity is the direct result of people bending their backs to accommodate for this really weird fact.

The equation that allows us to calculate stuff in special relativity!

Take two observers with identical rules and stopwatch, and aligned axes, but one is on a car moving at towards the $+x$ direction at speed $v$.

TODO image.

When both observe an event, if we denote:It is of course arbitrary who is standing and who is moving, we will just use the term "standing" for the one without primes.

Then the coordinates of the event observed by the observer on the car are:where:

Note that if $\frac{v}{c}$ tends towards zero, then this reduces to the usual Galilean transformations which our intuition expects:

This explains why we don't observe special relativity in our daily lives: macroscopic objects move too slowly compared to light, and $\frac{v}{c}$ is almost zero.

Programming is hard. To Ciro Santilli, it's almost masochistic.

What makes Ciro especially mad when programming is not the hard things.

It is the things that should be easy, but aren't, and which take up a lot of your programming time.

Especially when you are already a few levels of "simple problems" down from your original goal, and another one of them shows up.

This is basically the cause of Hofstadter's law.

But of course, it is because it is hard that it feels amazing when you achieve your goal.

Putting a complex and useful program together is like composing a symphony, or reaching the summit of a hard rock climbing proble.

Programming can be an art form. There can be great beauty in code and what it does. It is a shame that this is hard to see from within the walls of most companies, where you are stuck doing a small specific task as fast as possible.

A glitch is more precisely a software bug that is hard to reproduce. But it has also been used to mean a software bug that is not very serious.