## Provisioning a Windows Mobile PDA for developement

Michael Jacobsen
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. The old PDA was plug’n’play with respect to developing, that is, deploying from Visual Studio and so is the emulators. However, the iPAQ 214 did not allow me to deploy due to some security permissions.

## Project Euler 24

Michael Jacobsen
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. This problem is one of those that I solved using pen and paper after some research. I used the following Wikipedia pages: Permutation where I learned that there is a connection between the lexicographical order of a permutation and the factorial number system representation of that particular number Finally, you will need to remember that the Wikipedia articles both counts 0,1,2,… while the Euler problem counts 1,2,3,….

## Project Euler 35

Michael Jacobsen
To create the rotations I make a “detour” by converting the number into a string and then performing the rotations on the string. #light let primes_below v = Euler_utils.primes | Seq.takeWhile (fun p - p Set.of_seq let rotate number = let number_str = number.ToString() let len = number_str.Length - 1 seq { for i in [ 1..len ] do yield int64 (number_str.Substring(i) + number_str.Substring(0,i)) } let has_rotated set number = let numbers = rotate number Seq.

## Visual Studio 2008 GUID Macro

Michael Jacobsen
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? On the other hand it makes it possible for me to try out Visual Studio macro programming.

## Kensington Mouse Drivers Kills Click-Once

Michael Jacobsen
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. Another program that I have helped develop, FarmGuard, had an even more bizarre behaviour.

## Tail Recursion with F#

Michael Jacobsen
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 the solution to Project Euler problem 7 I have the following function let rec findprime primes test = if isprime primes test then test else findprime primes (test+2) Notice that the recursive call is placed as the very last operation in the function and it is therefore a tail call.

## Project Euler 48

Michael Jacobsen
In order to keep the numbers in check we use the rule that $$a \equiv v (\bmod m) \Rightarrow a b \equiv v b (\bmod m)$$ This rule is implemented in the powermod function. Note, that the powermod function is not yet “tail recursive” and is therefore vulnerable to stack overflow for (very) large b. #light let rec powermod a b m = if b = 0I then 1I else (a*(powermod a (b-1I) m)) % m let sum = let numbers = [1I .