scicomp.dk

This article tries to explain multiple concepts from statistics using a small Javascript illustration of the correlation of two variables.

The Khan Academy (link) was a pioneer in online learning. However, online learning really picked up speed in 2011 when a number of Stanford professors started a number of freely available online classes. I see it as a possibility to learn stuff in a structured way as a side project next to work. As I participate in courses I will add them to the following list with some remarks about my impression.

A Web Worker makes it possible to run Javascript code without blocking the user interface. That is, computations can be made in the background without locking the user interface.

All the scenes are version controlled on my GitHub page. You may do whatever with it - but I would like to hear about it - in the unlikely case that anyone do anything like that.

Subversion holds various information in .svn directories placed in all directories and sub-directories under version control. Sometimes it is desireable to clean out these files, for example, prior to emailing a zip of the files. I use the awesome tool Total Commander for the job.

During my Ph.D. I made a java applet demonstrating an inverse problem. This article brings the applet back.

When washing dishes, mowing the lawn or during commute I enjoy listening to podcasts. The following is a list of my favorite podcasts. I link to their homepage, but you can most likely also find them via iTunes or whatever podcast software you happen to use.

How far can you see when you are, say, 2 meters high? Lets find out assuming that we stand on a perfect circle with perfect visibility (and that we do not have refraction).

If you use more than one computer chances are that you use DropBox to keep a number of often used files syncronized and at hand.

The following is a list of the programs and tools that I install when I get a new computer or reinstall it. I have divided the list into two: The first list contains programs and utilities which can be downloaded and at least tried out for free (some are shareware). The second list contains the proprietary software that I use.

The iPad app-store is not the best with respect to search and comparison of the overwhelming number of available apps.

I had my old Windows Pocket PC 2003 stolen from my office and until now I have developed on the emulator. However, now the need for a physical device has come up and I got the HP IPAQ 214.

Project Euler problem number #24 deals with permutations in lexicographical order. A non-brute force approach involves a mixed base number system based on factorials.

To create the rotations I make a "detour" by converting the number into a string and then performing the rotations on the string.

I have never completely understood why Visual Studio had to start another (graphical) utility in order to create GUIDs. I'm all for the UNIX kind of small (text based) utilities than can be combined. Furthermore, this utility creates GUID in formats that are useful to C++ programmers. Why have they not used the built in Macro system?

For a long time I had a strange problem on my workstation. Some programs crashed before showing a window. For example, I was unable to run programs in the standard Visual Studio projects folder under my documents and settings. But they ran fine when moved somewhere else. I suspected some permission problem but I could not find and thus fix it.

The familiar for loop featured in most if not all impertive langagues is not part of most functional languages if any because it has the mutable loop index. The standard way of looping in F# is to use recursion.

In order to keep the numbers in check we use the rule that

My previous task switcher application had a serious performance problem as it was programmed in .NET. In order to start the small utility you had to load up the CLR and a bunch of assemblies (dlls). If you are a .NET developer it might not be that big a problem as most of the code was already loaded up. However, for general use it was not the best option.

F# has a nice syntax for creating sequences where elements are created on demand. For instance

What is the average distance between two points on a circle?

Problems 18 and 67 differs in their size, where problem 67 is so large that a (naive) brute force algorithm would not end within reasonable time. A simple algorithm shows it self if we goes from the bottom up. The problem formulation displays the numbers such that one looks at the numbers from the top going down.

F# has a lot of functionality for manipulation of lists. Here is my first attempt at the solution in F#.

To solve problem #23 I apply simple brute force and we get to play a little with F# sets. Find all abundant numbers below the given upper limit. Create a set of all sums of these numbers (with a small optimization where avoid computing both a+b and b+a). Then we make a set difference and sums the remaining elements.

I prefer to use the keyboard whenever possible. I have a two monitor setup and found myself moving windows from one monitor to the other using the mouse. However, using AutoHotKey I was able to do this by keyboard. Also I wanted to swithc easily to a particular window using the keaboard.

As warm-up to the question of average distance between two points on a circle I'll start out finding the average distance between two points on a line.

The problem is to deduce how the temperature changes (we will call this a temperature profile) at one place from measurements at another place.