I learned bookkeeping on Khan Academy with the two types of accounting: accrual basis and cash accounting. Assets, liabilities and equity words entered my head, currently busy with some Khan brain teasers.
And I managed to solve all currently published exercises on Khan Academy (129/129) :-) Kudos to my TI-89 which helped me out so many times! However, the unknown and legendary Black Hole badges aren't yet in my journeyer backpack... And to earn them, it is currently impossible because... the answer is ... hidden in Kahn's source code. Check badges/point_badges.py and exercise_completion_count_badges.py to unveil the secret...
Fabian Bellard's scientific web calculator is very powerful! I discovered it today while reading an advogato entry on him!
My academic career was a failure, but fortunately my khanacademic career is skyroketing :-). These days, I watched videos on Thermodynamics (in Chemistry section). I had a deep look at the Carnot Cycle, at adjabatic and isothermic processes and at the entropy definition, and the Maxwell's demon was lurking all the time.
I watched videos in history from French revolution, through Napoleon's rise and until his fall, and I felt sympathetic with people in the Haitian revolution and was scared by the dishonest debt they had to pay until 1947! In my previous history courses I had a more theoretical approach to the French revolution: we discussed in deep all Illuministic theories, but I completeley missed the stuff going on in Europe in 1789-1815. In the end, the Swiss constitution was enforced by Napoleon... I wonder how I could visit London and Paris without knowing what I do now... I practiced with exercises on the Academy site, too. To date, I watched 124 videos and solved 104 exercices. My goal is to earn at least one of the two unknown Black Hole badges!
As my one and one half year old daughter is learning by imitation, I decided to do the same! I equipped myself with an Aiptek 10000U (for about 130 Swiss francs) and bought Screenvideorecorder for another 40 bucks. I then created a tutorial video on how to compute the gamma factor of special relativity. English, audio and overall handling are experimental! (what else would you expect from dangermouse? ;-)
Excel SUMIFS function
It adds the cells in a range (range: Two or more cells on a sheet. The cells in a range can be adjacent or nonadjacent.) that meet multiple criteria. For example, if you want to sum the numbers in the range A1:A20 only if the corresponding numbers in B1:B20 are greater than zero (0) and the corresponding numbers in C1:C20 are less than 10, you can use the following formula:
=SUMIFS(A1:A20, B1:B20, ">0", C1:C20, "<10")
I recently saw SUMIFS used as an extended VLOOKUP with more than one cell which needed to match.
There is an interplanetary internet, and there may exist an internet between civilizations running at tachyonic speed. This time I ventured into
It starts with configuring the DNS servers with ones published at the OpenNIC project. You need to configure both primary and secondary DNS. Configuring only the primary DNS does not work, as the algorithm always chooses the DNS entry with lower network latency. After configuration, you still are able to surf on the usual Internet, but you also opened a little door to domains like .geek, .bbs and .telnet.
On the wiki of OpenNiC there are very few links, and in the beginning I was disappointed of such few links. Then I learnt of the specular search engine http://grep.geek. By searching for keywords like Blog or Chat you get to view some of the most accurate blogs and interesting chatrooms, especially for people who like to code.
Pioneer Anomaly solved with heat model
Pioneer space probes are the farthest human made objects from the Earth. In a previous post I explained how to connect to the JPL server via telnet and get their current distance from Earth.
Pioneer space probes feel an additional force towards the sun in the order of magnitude of about a_pioneer ~= H*c, which is also the one predicted by Modified Newton Dynamics theories to empirically explain the flat shape of radial velocity curves observed in galaxies. Currently, the the best theories to explain the galactic radial velocity anomaly are ones that look at the Universe at as inhomogeneous sponge. I hope the dark matters theories will be then finally wiped out, as to me they look as a revival of the theories on ether used before Einstein to explain the Michelson-Morley experiment. Also to have so much dark and heavy things passing through my body without interfering with it does not make me feel confortable at all. Springtime is time to give a compete cleanup to the Universe, it's needed once in a while :-)
The GPU project was looking for a solution of the Pioneer Anomaly. It ported source code from the Orsa Project made by Pasquale Tricarico from C to Delphi and experimented a bit with special physics without further success. It was not possible to replicate the linear shift of the signal received from the Jet Propulsion Laboratory dued to the pioneer anomalous acceleration towards the sun.
There is now an article here, that explains how the anomaly can be explained with 1970s computer graphics (basically a more advanced heat model as the one presented in the original Anderson et al. paper about the anomaly). The paper with the heat model explanation is on Arxiv and awaits confirmation from other scientific teams.
How seismic waves tell us about the inner Earth core
The GPU project was also experimenting with seismic sensors. Nanobit built one (picture) and I also built one with a 3D accelerometer on top of a coil. This series of 6 videos on seismic waves by Khan Academy explain very well the types of seismic waves, why Secondary waves travel only into solids (and in pudding :-), the curved path of refracted waves due to the density differences, the S-Wave shadow zone beginning from 105 degrees, and the P-Wave shadow zones. The seismic waves indirectly tell us how the inner Earth core is made, even if none of us digged that deep. Humankind only scratched the surface of Earth!
Learning the periodic table of the elements
The Fukushima accident made me courious of chemistry, and I sorted out an old periodic table of the chemical elements I was using in school. It has a list of the radioctive elements and their half decay time. I then realized that I did not understand anymore why the table was organized in this way. To be honest, I never understood it! I then took time to watch the introductory course on Chemistry by Khan Academy. The first ten videos explained me much more in detail how the periodic table works. In particular, I can do electronic configurations which was never taught in my chemistry course, and I understand a bit why metals are placed in the 'd' configuration. Metals and salts I already knew from before. And the f configuration at the bottom is for the heavier elements, which in principle should be moved between earth alcali and transitive metals, for the electronic configuration process.
IRC chat primer
I use on Gentoo weechat-curses as IRC chat terminal (emerge -av weechat-curses to install it).
Some topics in maths I did not knew or refreshed with Khan Academy are: Laplace Transforms, Convolution Theorem, Dirac Delta function, Taylor Theorem, Implicit differentation, insights in Chain rule, Conic Sections (foci of Ellipse, Hyperbola, and Parabola with Directrix), partial fraction expansion, l'Hôpital rule, surface integrals... I also learned a bit finance on forward contracts, futures and the margin mechanism I can use on the job. Sal, you are great!
Useful git hints
These git hints are taken from the Linux Magazine, article "Git in der Praxis".
git config --global user.name Danger Mouse git config --global user.email firstname.lastname@example.org
git config --global color.diff auto git config --global color.status auto git config --global color.branch auto
cd myproject git init git add . git commit
git commit -a -m "these are the changes" git push
git branch Refactor #switch to branch git checkout Refactor #back to master git checkout master
git checkout -b Refactor
git checkout master git merge Refactor
git tag -a "Tag_1.3.6" -m "new tag at version 1.3.6"
# on branch Refactor git commit git checkout master git pull git checkout Refactor git rebase master # repair conflicts git commit git format-patch master --stdout > mybugfix-patch.diff
I am also trying to understand a bit of this book:
The book is centered around Möbius transformations and Schottky circles. Möbius transformations
f(z) := (az+b)/(cz+d)are visualized as compositons of affine projections (az+b) and of projections on the Riemann's sphere 1/(cz+d) of the complex plane. They are at the ground of Beltrami disk (on page 379) and represent a non-euclidean geometry for which the parallel postulate is not valid. Schottky circles are generated by two Möbius maps which project one circle a into a circle A and another circle b into a circle B. With a breadth-first or depth first algorithm all set of reduced words (e.g AbBb reduces to Ab) are generated, and interesting pictures come out. Like the glowing gasket by Apollonius, invented in 220 BC, which is also the best way to pack as many tangent circles as possible (apollonian packing). The most famous fractal (Mandelbrot's apple) shortly appears at page 291.
When installing Debian Squeeze, the partition with Windows XP was not recognized. Normally I adjust /boot/grub/menu.lst but this time the file was missing.
os-prober grub-updatedid it....
As "scientist of information", you might find these tricks with M$ tools useful:
Creating SQL statements out of an Excel table with
=CONCATENATE("INSERT INTO tbdata(id, name, address) VALUES(";A1;"'";A2;"'";"'";A3;"'";");");
Or an update:
=CONCATENATE("UPDATE tbdata SET name='";A1;"');");
Lookup table in Excel
=VLOOKUP(C3;$L2:$O$25;3;FALSE);This formula looks up for the value in C3 in the table $L$2:$O$25 and returns values in the 3 column where C3 was found. It's a vertical lookup.
Importing Excel tables into access With File->Import->LInk External Table it is possible to import Excel tables into Access and then with SQL queries to extract data from them. However, I learnt that there is a limitation in the complexity of queries you can launch. I always switch from 'Design view' into 'SQL view' when creating queries.
For the interoperability of the Deltasql project, I setup a MS SQL server 2008 instance...
Installing SQL server
Downloading and installing it is easy, but at the end you need to assign a port to it, else the thing won't work. Might sound simple, but I assumed this step was automated by the install procedure. At best, you install it without touching defaults and as last step tweak it to open say port 2345 on TCP/IP protocol. Only after this step, you'll be able to connect with SQL Server Management studio client.
I still think that Oracle and Postgres are the high end of the database offer. However, I see once again how Microsoft is eating more and more of the lower segment. I know many little companies (10-30 employees) which now use some accounting solution based on SQL server. Still, sometimes at work I am puzzled and wonder if the transaction integrity of SQL server is always guaranteed, when under heavy load...
Tips to install Gentoo
I used an old CD to reinstall the latest Gentoo on andromeda, but failed due to some kernel issue with udev after several tries. I then decide to install Debian Squeeze, as I did not want to recompile everything on this old toaster (1GHz, 512 RAM) :-) As side effect I learned that it is always best to use the latest image of Gentoo install CD to get it running 8-)
An update on Fukushima Nuclear accident by Barry Brook is here.
In my humble opinion, the events shaking the world now, the nuclear accident in Japan and the arabic spring are epochal events, comparable to the fall of the wall in 1989 and 11 September attacks in 2001! They will shape the next decade...
I am chatting with a friend of mine in Japan, and found this interesting article for her, as I unfortunately can't do more from here: Fukushima Nuclear Accident - a simple and accurate explanation. The article states that there will be no risk, as the nuclear reactor is protected by three protective shells, which are still intact. The inner most shell is designed to contain the meltdown, if it should occurr. The building blasts which occurred in reactor 1 and 3 is simply hydrogen leaking from vents, and radiation is not a threat as it is easily dispersed in the time you spell R-A-D-I-O-N-U-C-L-I-D-E. The blasted building itself is just to protect the reactor from weather.
So, according to the article, there might be another explosion in reactor 2 due to hydrogen, but without further consequences. This because the control rods entered the core when the earthquake occurred and stopped uranium decay, and now it is a matter of removing the residual heat produced by reaction collaterals, which is done with seawater.
The building itself resisted an earthquake 7 times bigger than what it was designed to stand for. The problem was that engineers did not build a wall high enough to protect the diesel generators of the emergency cooling system from the tsunami.
I think openness shown by Japanese authorities is a major help in preventing the complete catastrophe. Exactly the opposite happened during Tschernobyl disaster. Workers sent out to manually insert control rods into the reactor came back browned by radiation reporting there was no reactor anymore to put the control rods in, but they were not believed by their chiefs. Also readings from dosimeters were ignored. Well, the smaller ones reported an 'E' for error, while the bigger ones broke immediately when they were powered on, as the watch hand jumped away. And there was the graphite everywhere around the building as witness that the core exploded. Not to mention the blue hyonized air on top of the reactor building!
Missing openness in chain of command is also the cause of another disaster in history (in 1686), the Vasa ship maiden voyage. The test for the ship's stability completely failed when sailors run on the ship's deck from one side to the other, but nobody dared to inform the king as he was behind the lenghtened ship design.
And remember that such disasters can happen in big software projects as well!
Deltasql 1.3.5 is released with some neat features: diffing of edited scripts implemented by phptreegraphext library and plotting the development tree of a project with PEAR Text_Diff library, both released under LGPL.
One of the pleasures of living in a small village in the mountains is to light the fire in the evening. Me and Marti, we like to watch flames and we straighten arms and say 'hhhhh' when we finally sense heat. Virgi is also happy to see that we managed to put fire only in the oven and not to the entire house.
Salman Khan is kind of modern Prometheus who stole fire from Zeus and brought to humanity. This time, instead of a torch he brought youtube videos with him, where he explains on a blackboard calculus, algebra, analysis, physics, biology and history from the simplest concepts to the advanced topics. The videos are for free and distributed in the best 'Open' manner. You can download 30 giga of videos if you like, or watch them on youtube. I personally am working through the 'Laplace Transform" videos, stuff which I never learnt before. I think the videos (and examples to work through) are very useful both to students but also for people who already attended university and would like to fill some leaks in their knowledge.
To enter Khan Academy, click here, pick out some video, I am sure you'll enjoy the relaxed style used by Khan to teach about anything, even the most advanced topics. To read more on wikipedia about it, click here.
* I was recovered three days at the hospital to cut off the cystifellea as I had too much fast food when I was student. They should put on any fast food the photos of my cystifellea and the stones they found in it to better advertise their meals. WhenI was waiting for operation, I "repaired" the laptop of my room's neighbour by simply taking off the battery so that it could restart. He called me a "PC doctor" :-) I think it is easier to repair computers than humans. In fact they do not cry if you do something wrong, nor they need anaestesia. Anyway, this is the introduction to the next paragraph :-)
Heart Transplantation for Andromeda
The screen on my laptop "andromeda" broke about three months ago after 9 years of duty. It is an XE3 HP laptop 1GHz, 512 MB RAM, 40 GB of RAM, on which I developed most of my Open Source projects. It was one of the first laptops sold with Windows XP, on which I installed first Red Hat 8.0, Suse 9,9.2 and 9.3, Debian 5.0 and ended with Gentoo. I also used the laptop during my study in Zürich, computed stuff with Maple for physics and maths courses, wrote "Hubble in a Bottle" for the zBox supercomputer, deltasql and GPU. . By chance I found an older XE3 laptop with 900 MHz, 256 MB RAM, 30 GB hard disk and decided to execute the operation "make one out of two", which works with basically any device of the same or similar kind (my uncle did it with 2 BMWs). The main advantage is that no matter how you work you end up with lots of spare parts and the disadvantage is you need space to store them.
There were two possibilites: 1. take the screen of the older laptop and put into the newer, or 2. take memory and disk from the newer to the older. I did it in sequence, as the newer laptop is faster (although the plastics has so many rips), but when I exchanged the screen, the laptop mainboard answered with a beeeep which basically was the official last breath of the newer laptop.
I then chose the second option, not really a choice as the newer laptop died. So that now I am writing this blog entry on the older laptop, which was by the way almost never used, plastic intact and shiny. It has also a robust appearance. I hope to keep this one for another ten years :-)
The point of developing software on old things is that if you get it working reasonably on it, you know that on newer hardware it will fly ! Also it remembers you that the heuristics you choose is way more important than the hardware you are on top.
Fractal dimension of Internet
* This is left as an exercise for the reader:
Write a bash script that rolls 4 dices with 255 faces (quite a big dice!) and concatenate them with a dot. Scan the obtained random IP number to verify if there is something behind it. If you find very weak computers with IP numbers starting from 127.x.y.z try to break into them (when you realize that you are attacking your own 'localhost', you can leave this part of the exercise). From the ratio of computers which answer compute how many computers are attached to the Internet. Call this number N.
Next modify the bash script so that instead of scanning the IP number, it traceroutes the random IP number, so that you get the distance from your computer to the other computer (in 'hops'). Compute an average distance and call it 'l'.
Ok now take Mandelbrot formula N ~ l^d/d and solve numerically for d. d represents then the 'Fractal dimension' of Internet. Well, according to Wikipedia, the Internet is not fractal, only the WWW is :-(
Feynman Lectures on Physics
I bought the books three years ago, and now finally found a bit time to read among them. Some things which I understand a bit more are: how Maxwell completed Faraday law when applying it to the condensator; how Einstein looked at the problem of a moving charge feeling a magnetic force if moving in proximity of a rod with electric current: for reasons of symmetry, if the rod is moving with current and the charge stays, the charge should still feel a force, but there isn't any force in classical physics which does it. Einstein then put an electric force and explained its existence with a relativistic argument (- charge are travelling, plus charges are at rest, - charges are travelling fast, therefore there is contraction of length, which implies an overall positive charge of the rod which generates an electric field which attracts the charge). The quantization of spin discovered by the Stern-Gerlach experiment and how spin states relate to linear algebra in quantum mechanics, how Schrödinger wave equation explains the valence model, how the heat equation works, Green and Stokes theorems applied to Maxwell equations...
* and I should rewrite the heat equation in simclimate as well...
GPU II preview for developers
* This is taken from the project news:
GPU is currently undergoing its 4th rewrite, codenamed freedom (3th was named solaris which reached version 0.963, 2th polaris, 1th unnamed). The preview package has version 0.5.0. This package is solely intended for developers as there is still no client working, just a bunch of unit tests.
The package should sketch the whole idea of the next generation GPU. Some people might be disappointed that GPU moves away from peer-to-peer to become a client-server architecture, but we believe this is the only drawback. The highlights of the coming release (probably 6 months from now) are:
- client/server architecture should allow scaling of nodes up to several thousands of clients
- client is in Freepascal and can be compiled on Windows, Linux and Mac OSX
- Server is in PHP/mySQL and runs everywhere where LAMP stack runs
- All software used to develop GPU II is Open Source and available freely
- The plugin architecture of GPU I is retained, although the plugin layer has been rewritten (available in preview) and plugins need to be ported as well
- Communication is entirely over HTTP, workunits can be downloaded, and resulting workunits can be uploaded via HTTP back to the server (available on GPU preview package)
- HTTP makes GPU transparent to most proxies, so that clients can run also in companies and not only at home
- GPU II retains features like channels (to run whiteboard, chat and sensor networks), job management, clustering services, all rewritten in light of the experiences done with GPU I (available on GPU preview package)
- GPU II will stay a multipurpose distributed computing architecture, so that any client and any server will support any computation (unlike the BOINC architecture)
- Each server should be able to support 40-100 clients according to some initial computations, the network should scale with number of servers
- One superserver will manage the whole network of servers
The package contains most of the server, communication layer client and server side, plugin layer clientside. we hope the release will fuel some more interest into the GPU project. Have fun!
* I read the book Crypto by Dan Brown and end up thinking how I would build my 'Digital Fortress' algorithm
Digital Fortress à la dangermouse
Depending on what to cipher, I would first choose the best compression algo, e.g. for text .zip, for pictures PNG or JPG (with loss) and apply compression to the 'plain text'. Then generate a hash of 'plain text' and append it. With ISAAC, a good pseudorandom algorithm I had the chance to analyze (initialized with some PBKDF2 of the 'key') I would generate a pseudorandom sequence of the same length of the compressed 'plain text' plus hash. Then XOR 'plain text' plus hash and pseudorandom sequence and finally execute a set of predefined statistical tests to ensure that at least the standard properties of white noise hold.
* To conclude I would cipher 'I love you' and send it to Virgi so that she can cranck on it :-)
New HTML Parser: The long-awaited libxml2 based HTML parser code is live. It needs further work but already handles most markup better than the original parser.
Keep up with the latest Advogato features by reading the Advogato status blog.
If you're a C programmer with some spare time, take a look at the mod_virgule project page and help us with one of the tasks on the ToDo list!