The semantic of Machine Learning

Today I learned again that most things in life are a matter of semantics… After some online lectures in Machine Learning techniques I discovered that what I call “Ordinary Least Squares” is generalized as a “cost function” and a simplified version of the “Newton Method” is refferred to as “Gradient Descent”. So, basically, the core of a supervised learned algorithm seems to be the choose of an appropriate “cost function” and the application of the most effective minimization algorithm.

How to see space occupied by directories in Linux Terminal

I learn and forget every tuesday afternoon the power of du and other Linux command line hacks. Hopefully writing this it will stick better in my brain lacking of real estate… To visualize the dimension of directories without opening the whole tree (and relative nests), the useful command is du -hs / with the wildcard that can be substituted by the **// to include a single level of subdirectories (or analogues for including multiple levels and files).

MacPro’s FirePro cards are actually a Radeon?

Today I learned about the new MacPro (2013 model) and the associated D300, D500, D700 graphic cards, that are compared over and over with Firepro W series (W7000, W8000 and W9000) by professional reviewers, thus making the MacPro 3500$ and rising price tag sound like a gift (FirePro W cards go from 500 to 1500 $ each).

To my knowledge, the difference between professional (ATI FirePro and NVidia Quadro) and consumer (ATI Radeon and NVidia GeForce) graphic cards is not in number or clock of processors or memory (the architecture is exactly the same, for example, for ATI Radeon 7970 and Firepro W9000 and D700 but the first cost one third of the second for the reason below), but :

Do not trust Google Analytics

I learned that Google needs some hours in order to track your website in Analytics. Even if in the “Tracking Code” section it says “Tracking Code is not Working” reporting a check performed in a given minute, actually sometimes you just have to wait some hours to start “Receiving Data” without furthermore tinkering with your web code. So just check the source code of your page, and if the Google Analytics snippet is included just give Google the time to update the tracking, without trusting too much the checking section.

The Speed of a V2 Rocket.

Today I learned that the a V-2 rocket was much faster than the speed of sound, in fact the max speed was more around Mach-4 (5,760 km/h to be more precise, according to wikipedia), and flied using a water-ethanol compund and liquid oxygen (!). Some survivors were in fact reporting the hitting of the blast in utter silence followed by the sonic boom and the sound of hell breaking loose.

Universality and few-body systems

The three Borromean rings. There are some properties of few-body systems that are “Universal”, so shared between all few-body systems that feel an attractive interaction (with certain boundary properties for defining eventual spin-orbit and isospin). An example of this behavior are the Efimov states of three-body systems: when an interaction loosely bound two bodies, the three-body system have a precise spectrum of excitation. This spectrum is observed in three nucleons systems like Helium-3 and Triton, since the two-body system, the deuteron, is loosely bound (for nuclear scales).

Sterile neutrinos give birth to new Physics

Today I learned something more about sterile neutrinos, and the latest advancement to the quest of finding them.