jerichoblog

How many Asian countries can you name?

2007-08-27T17:13:00.001+01:00

Much more challenging than the 50 states quiz. If you think you know Asia, this site will really test you. Watch out for the former Soviet states and the territories of South East Asia.

read more | digg story

Name the 48 Counties of England

2007-07-30T15:23:00.002+01:00

Continuing the venerable tradition of online geography quizzes, this page tests your knowledge of the 48 Ceremonial Counties of England. As you name the counties, the names are pinned to a map of England.

read more | digg story

SIM card rejected? Phone doesn't ring?

2007-03-29T15:52:00.000+01:00

I have a very basic mobile (cell) phone, bought simply to make and receive phone calls. After a year, I started getting the message "SIM card rejected" with increasing frequency, requiring me to restart the phone. Of most concern to me was that I might be missing calls during the periods of rejection. I took the phone (a Nokia 3120) to my local Orange shop where I was told that the phone might be dying on me and that I would have to get a new one. I was not pleased!

A few more months elapsed and I found that the phone had stopped ringing, though the vibrating alert continued to work. I checked my phone settings to make sure that it was set to ring. Everything seemed to be set up OK, and the phone was still producing bleeps, suggesting that the hardware was working properly. Again, I took the phone to the Orange shop and was told I'd have to buy a new phone. Given my belief that the hardware was operational, I decided not to give up on the phone. I turned to the user manual and found how to restore the factory settings. Having done this, my problems disappeared. Note that the contacts list and text messages stay intact after the restoration. If you have a similar phone, I've copied the instructions below:

Restore factory settings
To reset some of the menu settings to their original values, press Menu, and select Settings and Restore factory settings. Key in the security code and press OK. Note that the data you have keyed in or downloaded, for example, the names and phone numbers saved in the contacts list are not deleted.

More troubleshooting information is available from Nokia.

Amateur Mathematicians

2007-02-13T22:18:00.000Z

Pierre de Fermat is the best known amateur mathematician, but the story of Grassman is much sadder. Something of a mathematical Van Gogh, he created the subject of linear algebra single-handedly, devised the first axiomatisation of arithmetic, and much else besides. His work was rejected by almost all professional mathematicians of the day, including Möbius and Kummer. Unlike Van Gogh, he didn't end up killing himself, but became a noted philologist instead!

Another case of a neglected mathematician is Kurt Heegner who solved Gauss' class number problem for imaginary quadratic fields (finding all nine such fields of class number 1). His proof was dismissed by the mathematical community until 1967 when Harold Stark developed a proof and showed it to be equivalent to Heegner's. Unfortunately, Heegner had died two years earlier.

How to log in to your Motorola WR850G wireless router

2006-07-24T19:35:00.000+01:00

Question

Dear Sir/Madam,

I can't access the control panel on my WR850G. I bought the unit in March and managed to set it up just fine. I enabled WPA-PSK and MAC-based authentication and disabled DHCP (as I was using another device as a router). I've had no problems with it since then, until just now when I bought a new laptop.

Naturally, I needed to access the control panel in order to enter the MAC address of my new wireless adapter. Unfortuately, nothing happens when I try accessing 192.168.10.1 on my web browser (even using the machine which can get a wireless service from the router). I get a ping response from 192.168.10.1 if I change my IP address to 192.168.10.2.

I've tried resetting the router (by holding the reset button for 30 seconds while the power is on). This seems to have no effect and the router continues to transmit the old SSID.

I've also tried running the installation utility which came with the router. This works OK until it gets to the "detecting router" stage, and then stops.

Basically, I can use the router fine as a wired switch, and I can use it as a wireless access point with exactly one wireless adapter (the one whose MAC address I'd entered into the router using the control panel). I cannot access the control panel, hence cannot add the MAC address of my new laptop.

I would very much appreciate any help you can provide me with in solving this problem.

Answer

Hello Gihan
try this hook the router to the xp computer remove the modem from the router so just 1 eithernet cable going from one of the 4 lan ports on the back of the router and the other end to the back of the pc now go to start , then click on control panell
now click on internet and network connection then click on net work connection
or you may just see network connection now right click the local area connection and go and left click properties
now high light internet protocal tcp/ip and then click on properties
now put the dot in use the following ip address Then type each of the next but subnet mask should auto populate
IP=192.168.10.4
subnet mask 255.255.255.0
default gateway=192.168.10.1
Then click on ok then close
now open up internet exploror or mozilla and in the address bar type 192.168.10.1 and see if you can get to the log in screen if you cant you will need to call the # below and talk to our tech support team there incase the router is faulty
let them know what we already did so they dont have to redo what weve already done
Thank you for chooseing motorola
If you need further assitant please respond to this email or contact us by 1877 466 8646
Thank you for choseing motorola you have a great day
Charlotte

Using Xfig with LaTeX

2006-07-23T17:27:00.000+01:00

Xfig is a program used to create drawings with lines, arcs, and splines. LaTeX is a document preparation tool. How do you use them together? I'll discuss a technique which allows you to use LaTeX strings within your figures (for mathematics, Greek text, etc). The first thing you'll need is the following entries in your LaTeX preamble:

\usepackage[dvips]{graphicx}
\usepackage{color}

The first package is essential for working with graphics in LaTeX, the second is needed because Xfig enters colouring commands into its LaTeX output (even if all the output is black). Fire up Xfig with the following options:

xfig -specialtext -latexfonts -startlatexFont default

If you don't want to do this every time, just add the following entries to your .Xresources file:

Fig.latexfonts: true
Fig.specialtext: true

Go ahead and make your figure. You can enter LaTeX strings as text, these will later be converted by LaTeX into beautiful mathematics.

When you're done with the figure, save it in the same directory as your LaTeX file, let's suppose you name the figure myfig.fig. Export the file as "Combined PS/LaTeX (both parts)". This will make two new files, myfig.pstex and myfig.pstex_t. When you need to use the file in your LaTeX document, enter something like:

\begin{figure} [ht]
\input{myfig.pstex_t}
\caption{My figure}
\label{some_label}
\end{figure}

You might not be able to see the effects in the dvi file, but you should be able to see your figure if you run dvips mytexfile.dvi to create a PostScript file.

Working with PDFLaTeX

Similar principles apply if you want to end up with a pdf. Of course one simple solution is to run ps2pdf on your ps file from the previous section, but you may end up losing some pdf-specific features, such as hyperlinks. The recommended alternative is to run pdflatex instead of LaTeX. You'll need some changes to the preamble:

\usepackage[pdftex]{graphicx,color}
\DeclareGraphicsRule{.pdftex}{pdf}{*}{}

You use Xfig much as before, but this time you export the figure to "Combined PDF/LaTeX". This will produce files myfig.pdftex and myfig.pdftex_t. The latter file replaces myfile.pstex_t in the body of your LaTeX document. When using pdflatex, make sure that your Xfig is in the correct orientation (usually portrait).

Most of the information is this post was gleaned from the Xfig website, which contains much more information on using LaTeX with Xfig.

Creating a Bootable Windows XP Setup CD

2006-07-15T15:23:00.000+01:00

There are a number of reasons why you may need such a CD:

Your copy of Windows came preinstalled, and you'd like to have a backup in case something goes wrong.
You want a 'slipstreamed' setup disk, i.e. a setup disk which will install XP Service Pack 2 as part of a full install.
You want access to the Windows Recovery Console.

I actually fall into the last category — having decided to remove Debian Linux from my computer, I also wanted to remove its boot loader, GRUB, and replace it with the Windows boot loader. Unfortunately, this can only be done using the fixmbr program which comes with the Windows Recovery Console!

If you already have a Windows Setup CD, then all you need to do is to follow the instructions given in Paul Thurrott's web site. However, if you have a preinstalled version of Windows, you may find that the contents of the Setup CD are located somewhere on your hard drive. In my case, (with an Acer TravelMate 4151LMi) the Setup files are in C:\i386. You need to follow the instructions in Bart Lagerweij's web site to create a bootable CD from the Setup files.

If you have SP2 then you'll also need to 'slipstream' the Service Pack. Unless you already have the Service Pack file, you'll need to download it from Microsoft. Instructions for downloading and slipstreaming are given as Steps 2 and 3 in Paul Thurrott's web site (you need to modify the instructions a little to work with Bart's procedure).

Remote Mathematica use for Linux / Cygwin

2006-05-15T08:30:00.000+01:00

Unless you can afford to shell out the long green for a Mathematica licence, you may be in the situation where you have to be physically present at a University computer in order to use it. The other possibility is to remotely log-in via ssh and the X Window system. If you choose the latter path, it is crucial that you have the appropriate fonts installed on your computer, otherwise Mathematica will present you with goobledegook instead of mathematics.

I'm assuming here that you are using Linux or Cygwin. I don't know how this works for native Windows, but would be happy for any enlightenment. As a root user, carry out the following commands:

The first step is to download the Mathematica fonts from the Mathematica web site.
Create a Mathematica subdirectory of /usr/lib/X11/fonts
Copy the downloaded files to /usr/lib/X11/fonts/Mathematica
Untar the files (with tar zxvf filename, for each downloaded file called filename).
Make sure the permissions are set correctly on the files. You may have to run chmod -R 750 /usr/lib/X11/fonts/Mathematica. Essentially, just make sure that the new font files have the same permissions and ownership as all other font files on your system.

This is where the instructions for Cygwin and Linux vary. For Cygwin, enter the following lines into your .xinitrc file as an ordinary user (the file will be in your home directory):

xset fp+ /usr/lib/X11/fonts/Mathematica/BDF
xset fp+ /usr/lib/X11/fonts/Mathematica/Type1
xset fp+ /usr/lib/X11/fonts/Mathematica/PCF
xset fp rehash

You will then have to restart X for the changes to take effect (or, if you are impatient, you can enter the above lines into your command shell for an immediate change).

Troubleshooting: You may find that the font paths are set correctly when you enter the above commands (check by typing xset q), but aren't set properly when you restart Cygwin. This is probably because you aren't starting X from the startx command, and hence .xinitrc is being bypassed. You'll have to modify a different file. If you're using the fvwm window manager, place the above commands in the .xinitrc-fvwm file instead. If you use the XWin window manager, add the lines to your .bash_profile (this is a set of commands which is run for every login shell). If you use many window managers, it may be more efficient to keep the above lines in a separate file (e.g. ~/.mathemata-fontset) and then run this file from each of the startup files.

The above technique will work with Linux too, but is somewhat non-standard. The standard approach for Linux would be to enter the font paths into your XF86Config file (or your xorg.conf file if you use xorg). Just add the following lines to the "Files" section of /etc/X11/XF86Config (or the appropriate configuration file on your system):

FontPath "/usr/lib/X11/fonts/Mathematica/BDF"
FontPath "/usr/lib/X11/fonts/Mathematica/Type1"
FontPath "/usr/lib/X11/fonts/Mathematica/PCF"

That's it!

Firefox keyboard scrolling problems?

2006-05-05T22:45:00.000+01:00

If you don't want to the read the whole article, I'll sum it up briefly: turn off caret browsing!

Firefox has a feature called caret browsing, which can be enabled / disabled by clicking F7 or ticking the checkbox under Tools -> Options -> Advanced -> General and "Allow text to be selected with the keyboard" (or "Always use the cursor keys to navigate within pages" for Firefox 2). This is somewhat misleading as text can be selected with the keyboard even without caret browsing. The main difference is that the keyboard navigation keys (e.g. the cursor keys, PgUp, etc.) will affect the caret rather than the page location.

In short, if you find that the keyboard navigation keys don't act as you expect them to, turn off caret browsing.

Reviews: Kernighan and Pike, The UNIX Programming Environment

2006-04-09T15:39:00.000+01:00

A real classic of its genre, this is the first book ever written on UNIX, published in 1984 and still in print today. While some of the details may have changed, the book remains relevant by expounding timeless principles of good programming practice.

The authors are true gods in the pantheon of computer science. They worked together at Bell Labs in the early days of UNIX and have since been instrumental in the development of computing. Rob Pike co-developed UTF-8 with Ken Thompson and now works at Google. Brian Kernighan[1] co-wrote The C Programming Language with Dennis Ritchie, a book widely regarded as the bible of C. Kernighan is now a professor at Princeton University.

The wit and sagacity of these men is evident in their book. Each new idea is fully reasoned out and they take delight in presenting novel solutions with the minimum of raw material. My favourite example is their 'bundle' shell script from Chapter 3. This is a 10-line program which creates self-extracting archives by using the principle of 'here documents'.

In content, the book is split into two parts. The first four chapters deal with the details of using UNIX: simple commands, the file system, interacting with the shell, pipes, redirection, and a little on awk, grep, and sed. Chapters 5 through 9 are more directly concerned with programming. In particular, shell programming is covered in Chapter 5, culminating in the development of a version control system! Chapters 6 and 7 discuss the stdio library and UNIX system calls. Chapter 8 brings it all together with the implementation of 'hoc', a programmable calculator. Kernighan and Pike take the time to develop it organically, building up hoc from a simple four-function calculator. This chapter introduces the yacc parser generator and the lex lexical analyzer generator. As a matter of historical interest, document preparation using troff is discussed in Chapter 9 — this system is used to create UNIX manual pages.

The only real drawback of this 20 year old book is that some of the examples don't work correctly, or are irrelevant. It is unlikely that you will use the 'mail' command to read your mail, or the 'ed' editor to write your documents. Running 'od -cb .' no longer prints out the contents of the directory-as-a-file. However, these are minor issues. Learning 'ed' is a good introduction to regular expressions, and you may have occassion to use 'mail' in a shell script!

If you only buy one book on the UNIX programming environment this summer, make it this one.

[1] the 'g' is silent

Internet Tools, Web2.0, and the new Community

2006-04-06T15:13:00.000+01:00

Water, water, every where,
And all the boards did shrink;
Water, water, every where,
Nor any drop to drink.

Samuel Taylor Coleridge - The Rime of the Ancient Mariner

Since the dawn of the Web we've struggled to find useful information from amongst the flotsam of irrelevant websites. The first torchbearers to guide us through this mess were search engines, tracing their lineage to the pre-Web Internet. The modern age has sprouted a new generation of tools and services which depend on the collaborative force of diverse users. Collectively, these advancements are being referred to as Web 2.0. Some of the more sucessful manifestations of this ideal include Wikipedia, blogs, del.icio.us, flickr, StumbleUpon, Freecyle, and Slashdot.

These sites broadly fall into two camps: (1) 'Web Finders' deliver up relevant Web pages. Examples are Google, del.icio.us, and StumbleUpon; (2) 'Web Tools' are Internet resources which provide a useful service. Examples are Wikipedia, flickr, and Slashdot. Naturally, there is a certain ambiguity. Slashdot could fall into either of the two camps.

Many of the above examples will be familiar to the majority of users. I'll illustrate Web Finders and Web Tools with two lesser-known examples from each group:

StumbleUpon

Traditional search engines suffer from one major drawback - they can only show you what you're looking for. In the words of Pablo Picasso, "Computers are useless. They can only give you answers".

We've all had the experience of being alerted to a cool website by a friend or a magazine. The type of website we never would have found by googling for 'cool website'. The point is that we all have a different notion of what is cool. There cannot be a canonical list of great sites that would suit all tastes.

Coming to our rescue is StumbleUpon. You mark the sites you like and those that you don't. Based on your personal preferences, StumbleUpon will suggest sites which like-minded Stumblers enjoy. A simple idea brilliantly executed.

Freecycle

Freecycle is a great example of a global technology acting on a local level. In a sense, it is a marketplace for free goods, bringing together people with things to give away and people in need of those items. I belong to my local freecycle group in Oxford, England. As I'm without a car, Freecycle is a great way for me to get rid of unwanted possessions! When I have material needs you can be sure that Freecycle will be my first port of call.

Conclusion

In all cases, the new breed of websites make positive use of community spirit. In our modern age of nuclear families and increasing alienation, it is as though the Web has stepped into the breach to create new communities of like-minded individuals. Each such community carves out its own slice of the Internet, adding order and cohesion where once there was chaos.

For the moment social networking is in the ascendency, but the one certain truth about the Internet is change. It is unlikely that social networking will disappear, but it will ultimately transform into something else. The leaders of tomorrow's Net will be at the helm of this change.

web 2.0
stumbleupon
freecycle
community

Thunderbird Upgrade Problems - version 1.5

2006-04-05T20:54:00.000+01:00

You may have experienced problems upgrading from Thunderbird 1.07 to version 1.5. I did! In particular, upgrading caused failure of Enigmail, and there were issues using the United Kingdom / Great Britain spell checker.

One thing to bear in mind is that you will not have to delete your old Thunderbird profile, which will save much heartache if you can't recover your profile.

If you have problems after installing Thunderbird, follow these simple steps:

Start by uninstalling Thunderbird (for Windows users this would involve the Add/Remove programs applet from the Control Panel).
Delete the main Thunderbird folder, which should be located at C:\Program Files\Mozilla Thunderbird.
Reinstall Thunderbird.

Then reinstall your extensions. If this doesn't work, rinse and repeat.

The spell checker is particularly problematic. I found that the UK dictionary wasn't included even though I chose to download the British version of Thunderbird. Moreover, the spell checker marked every word as being misspelled. You can find the appropriate dictionary from Mozilla's dictionary page. Install the file as you would for any other extension. Note that the dictionary will not appear in your list of extensions. To activate the British (or other) dictionary, go to Tools → Options → Composition → Spelling. Make sure "Enable spell as you type" is checked, then choose the dictionary you want. You may have to restart Thunderbird a few times before the dictionary begins to work properly.

Reviews: Bartle and Sherbert, Real Analysis

2006-04-04T14:44:00.000+01:00

This is a superb introductory text on real analysis. It is the recommended text for first year undergraduates at the University of Oxford and covers sequences, series, limits, continuity, differentiation, integration, and uniform convergence. There is even a short section on Lebesgue integration.

The book is rigourous yet readable, contains copious exercises and is complemented with short biographies of famous mathematicians, adding a human touch to the proceedings.

The authors eschew the more informal style of some introductory texts and prepare the students for the Definition - Lemma - Theorem technique of higher mathematics. It can be somewhat terse in places, but this has the advantage of focussing the student's mind on the essentials.

Miscellaneous Pages

2006-04-04T11:40:00.000+01:00

Random matter:

Moon at St Barnabas
Daylight Saving Time - Crime, Larks, and Energy
First Day

Mathematics Pages

2006-04-04T11:36:00.000+01:00

My mathematics posts. Also see the mathspages on my main website.

Using Xfig with LaTeX
Remote Mathematica use for Linux / Cygwin
Reviews: Bartle and Sherbert, Real Analysis
Partial Preorders
Simple Margin Adjustment in LaTeX
Elementary Wavelet Analysis

Computer Pages

2006-04-04T11:20:00.000+01:00

Recipe Pages

2006-04-04T11:18:00.000+01:00

My food posts:

English-Style American Hamburgers
Gihan's Fruity Penne With Chorizo

English-Style American Hamburgers

2006-04-04T11:15:00.000+01:00

This is my own take on a classic American dish. I substitute (English) muffins for burger buns and use real cheese instead of American cheese-substitute.

Ingredients (serves two)

250g (½ lb) lean minced beef
1 clove garlic, finely chopped
3 sticks of celery, sliced
4 slices (hand-sliced!) mature Cheddar
1 handful of chopped red onion
2 (English) muffins
salt, pepper, olive oil

Method

Gently mix the beef, olive oil (about 1 tbsp), salt, pepper, and garlic in a bowl. Divide the mixture into two balls and press into patties. As with dough making, this is a sensual delight, so enjoy the experience.

Take a skillet of generous size and line it with olive oil. Place the pan on a high heat then add the patties when the oil is hot. You will need to turn the patties once, and be aware that the insides may not be cooked even if the surface is crisp — hence you should keep cooking for about five minutes after the outside seems done.

Prepare the muffins by cutting down the middle and thinly spreading Dijon mustard. Add the cooked patties followed by layers of cheese, red onions and celery. The celery will spill over onto the plate, this provides a little decoration. Now eat with your hands.

Converting DVDs to mp3s

2006-04-03T12:30:00.000+01:00

Scenario: you have a DVD and you'd like to make an mp3 of a particular track / soundclip. The simplest solution (especially for Linux users) is to use mplayer and lame, which are freely available and open source.

Basic Ripping

Mplayer will produce a wav file from the DVD, and you can then use lame to convert the wav file to an mp3. The general mplayer command line is as follows:

mplayer $SOURCE -ao pcm -af resample=44100:0:0 -aofile $WAVFILE -vc dummy -vo null

Here $SOURCE is the recording source and $WAVFILE is the output file.
There are many ways of specifying the source. If you wished to record chapters 2 to 4 from dvd title 2, the appropriate invocation would be:

mplayer dvd://2 -chapter 2-4 -ao pcm -af resample=44100:0:0 -aofile outfile.wav -vc dummy -vo null

The final stage is conversion from the wav file to the mp3 file. You do this using lame, and the correct command is:

lame $WAVFILE $MP3FILE

where $MP3FILE is the desired mp3 file name.

Mplayer and lame are available for Windows, but there may be problems playing the later chapters in a DVD, as there seems to be a 2Gb limit imposed by the underlying software.

If you don't have Linux, it may be better to try a non-free alternative. A search through Tucows comes up with a large array of Windows tools, including "A1 DVD Audio Ripper", "AoA DVD Copy", "DVD Audio Extractor", and many others!

Advanced Ripping

The previous section should be sufficient for most purposes, but there are a few more tricks which may make the process smoother. Linux users can eliminate the need for a large intermediate wav file by using named pipes. First create the named pipe with

mkfifo $WAVFILE

You can now issue the lame command, followed by the mplayer command (preferably on different consoles). Delete the $WAVFILE file once you've finished the process.

Mplayer has a large variety of options. We've already seen how to specify the chapters you want to record. Another alternative is to specify the seek time. For example, to start recording from 1hr 30mins 40s, issue the following command:

mplayer dvd://2 -ss 01:30:40 -af resample=44100:0:0 -ao pcm -aofile outfile.wav -vc dummy -vo null

To find out more about mplayer, read the manual page.

Moon at St Barnabas

2006-04-01T22:55:00.000+01:00

Moon at St Barnabas
Originally uploaded by Gihan Marasingha.

We've spent some time looking at the Moon in Oxford. Here's a calm picture of the Moon sitting by St Barnabas church tower in Jericho, Oxford. This photograph was taken by Maggi and we can see an acacia tree in the foreground.

Daylight Saving Time - Crime, Larks, and Energy

2006-03-31T18:40:00.000+01:00

This Sunday, clocks go forward at 2:00am in most of the U.S. The biannual clock-changing has been marked by controvery since it was first conceived by Benjamin Franklin in 1784. Many late-night revelers feel cheated of an hour's drinking time. This has lead to Time Change Saturday riots in Athens Ohio, witnessing skirmishes between armed police and rowdy students.

However, the general trend is that Daylight Saving Time reduces crime. One study in Washington DC found a 10 to 13 per cent decrease in violent crime. This is due to lighter evenings, making crime more detectable.

Unfortunately, there is a downside for 'larks' — those who naturally wake early. They are genetically more aware of light and will have a harder time adjusting.

Finally, this is the last year that clocks 'spring forward' on the first Sunday of April. From 2007, the time change will occur on the second Sunday of March, with a corresponding alteration in the Fall. This is in accordance with the Energy Policy Act of 2005, which hopes to give a 1 to 2 per cent saving in household energy use by reducing the need for electric lighting in the evenings.

A Reformed Linux Zealot Speaks Out

2006-03-09T08:26:00.000Z

They say there's nothing worse than a reformed smoker. Perhaps that's true, but it's a great thing to be a reformed Linux Zealot. Actually, not using Linux is akin to smoking and drinking all you want and generally having a big party (note this is a simile - I don't smoke at all and drink only in moderation).

I take this opportunity to share a tale with my Linux brethren in the hopes that I may lead you to the land of Easy Computing in far off Redmond (though Cupertino works too). As you read my story, you will come across familiar horrors such as driver woes, kernel compilation, and writing scripts just to get basic functionality. I begin with a brief chronology of my computer use:

c. 1988 Sinclair ZX Spectrum 128K +2 (died in action)
c. 1992 Acorn Electron
c. 1994 PC (Western Systems 486 SX 33 MHz, 4Mb RAM, 270 Mb hard drive)
1994-2005 A succession of upgrades / cannibalisations with second hand PCs
2005 Acer Travelmate 4151LMi Laptop (Pentium M 725 @ 1.6 GHz, 512 Mb RAM, 60 Gb hard drive)

I was introduced to Linux in 1996 on university computers at Imperial College, London. Having dabbled in C programming on the Windows platform, I found Linux to be a breath of fresh air. At the time, a programmer had to use many system calls to get things done properly with Windows. All this was transparent to Linux, and it was really just a case of coding in ANSI C. Even more wonderful for a cash-strapped student was the fact that the gcc compiler is free.

At some point in my undergraduate career, I decided to go dual-boot and opted for Debian (either Slink or Potato, I forget which). In retrospect, this was a terrible choice as a first Linux distribution. At the time, Debian was very much a hardcore distribution and only for the brave souls who wanted to get down and dirty with Linux. My first installation took a couple of very stressful days, and involved a steep learning curve. A major source of stress was the worry that I would accidentally format my Windows partition, or that the resizing process would damage it somehow. These days, I would strongly recommend backing up data before messing about with partitions.

Linux was not entirely hardware-friendly. In particular, I spent many hours (days?) getting sound, joysticks, and printing to work properly. Only by recompiling the kernel was I able to get sound to work properly. Things are somewhat easier now with the introduction of kernel modules, but it's still something of a hassle.

I switched to Red Hat 6.2, and then to Pink Tie 9 (a Red Hat 9 clone). This distribution was sufficiently capable that I dropped Windows 95 in favour of it, only returning to Windows when I needed to use MS Office (which was infrequently). I saw further improvements with Debian Woody and then Debian Sarge. By the time I got to Sarge, Windows was a distant and rather unpleasant memory.

As a mathematician, my main applications are: a web-browser and email client, emacs (a text editor), LaTeX (a typesetting application), and Maple (a computer algebra package). Unencumbered by reliance on MS Office, I was entirely free to use whatever operating system I desired. Ironically, it was this very freedom which ultimately led me back to Windows.

My brand-spanking new laptop had a SATA drive. Unfortunately, this drive was not recognised by the Ubuntu Hoary Hedgehog installer (Ubuntu being my current Linux distribution of choice). Instead I installed Debian Sarge. The problem was that the system still needed considerable work to support my wireless card and didn't have xv support for my graphics card.

Back in the dual Linux/Windows 95 days, I would have had no option but to spend hours configuring the drivers, recompiling the kernel, etc. However, I suddenly found myself working with a perfectly functioning Windows XP Pro. Other than some relatively minor tweaks, XP worked fine. It was a busy time for me with deadlines fast approaching, so I ditched Sarge in favour of Windows XP. I haven't looked back.

Don't misunderstand me, I didn't drop open source software. I didn't even completely ditch Linux. Other than the operating system, the only commercial software I use is Maple (so no change from my Linux days). When I need the power of Linux, I turn to Cygwin, a Linux-like environment which sits on top of Windows. The advantage of Cygwin over a virtual machine is that Cygwin uses the Windows filesystem, device drivers, and system calls, but presents a Linux-like API to applications. In effect, it is Linux but without the hassle!

I now find that I spend much more time getting things done, instead of tweaking my Linux system to the nth degree. If Linux is to find mainstream acceptance, developers should make hardware support a priority. Ubuntu seems to be going in the right direction by offering the xorg server and generally good automatic hardware configuration. The turning point will come when major computer manufacturers produce good machines with Linux preinstalled.

The point of my article is that in these days of free/open source software, the operating system has become less important, not more. Applications are the king and they are no longer tied to particular operating systems.

Partial Preorders

2006-03-05T21:27:00.000Z

How many transitive and reflexive relations (partial preorders) are there on a set of three elements? This question was recently posed in a first-year maths problem sheet at the University of Oxford.

It can easily be shown that there are 64 reflexive relations on such a set, and one can determine which of them are transitive. This is a bit of a pain, so I wrote a Maple worksheet to simplify the process.

The worksheet computes all relations on a set of 3 elements and represents them as matrices. Without loss of generality, the set of 3 elements is S = {1, 2, 3}. A relation is then represented by a matrix A with entries from {0, 1}, where A[i, j]=1 iff i ~ j.

With this representation, a matrix is reflexive iff the diagonal entries are all 1. The transitivity condition is a little more complicated, but can be coded without much difficulty.

It turns out that the answer is 29.

Gihan's Fruity Penne with Chorizo

2006-02-25T16:55:00.001Z

Here's a delightful meal I whipped up this lunchtime. It was very scrummy, so I thought I would share it. The recipe below is for two people.

You will need:

one chorizo sausage
200g penne
two nectarines
a handful of corriander

Boil the penne according to the packet instructions. While you're doing this, slice and skin the chorizo (the slices should be about 5mm in thickness). Fry them gently in a little olive oil. Slice the nectarines and cut each slice in half. Coarsely chop the corriander.

When the penne is boiled, drain it and add to a warmed plate. Add the chorizo and drizzle the chorizo oil over the pasta. Add the sliced nectarines and corriander. Season with a little salt and pepper.

This dish is delicious with a nice herb salad consisting of baby spinach, roquette, corriander, lollo rosso, chives, and frisee. For a light dressing, just add a little olive oil, balsamic vinegar, and salt.

Simple Margin Adjustment in LaTeX

2006-02-25T11:01:00.001Z

LaTeX enforces beauty upon its documents, sometimes to the detriment of practicality. By default, LaTeX margins are extremely generous. This leads to good-looking documents, but there are occasions when it may be better to have smaller margins —— for instance, if you want a document to fit entirely within one page.

Page layout with LaTeX is a complicated matter. A cursory glance at the LaTeX documentation shows that the layout is determined by 11 different parameters. However, I find that the following commands are sufficient for most purposes:

\addtolength{\textwidth}{ain}
\addtolength{\hoffset}{-bin}
\addtolength{\textheight}{cin}
\addtolength{\voffset}{-cin}

where a, b, c are numerical quantities such that a=2b. The effect of these commands is to increase the extent of the horizontal material by a inches and increase the extent of the vertical material by c inches.

If you want more control over your margins, then I highly recommend the LaTeX geometry package. The author of the geometry package is careful to ensure that all page settings are correctly assigned, leaving a straightforward interface to the user. As a simple example, add the following to your preamble:

\usepackage[hmargin=3cm,vmargin=3.5cm]{geometry}

This sets the left and right margins to be 3cm and the top and bottom margins to be 3.5cm. Full details are set out in section 5.3 of the geometry user manual.

Easing the Firefox / Adobe Acrobat experience

2006-02-24T23:07:00.000Z

If you use the Firefox web browser, you may experience surfing woes with the Adobe Acrobat plugin. The plugin is notoriously buggy and often hangs my web browser. However a simple solution is at hand which requires no downloading at all!

The simplest solution is to ask Firefox always to open a pdf document in a separate Acrobat window. To do this, open the Tools menu and select the Options... dialog box. Choose the Downloads tab and click View & Edit actions. From here, you can tell Firefox what to do whenever it is presented with a particular type of file. Naturally, this extends way beyond Adobe Acrobat and can be used for many different file types. Of course, it would be easier not to install the plugin in the first place, but this approach provides one with a certain degree of flexibility. For those who require an extra degree of flexibility, you may wish to try the PDF Download Firefox extension. This queries the user on what to do each time a pdf link is clicked.

Easy Get Mail - Multiple Thunderbird accounts made easier

2006-02-01T15:34:00.000Z

Like many Thunderbird users, I have multiple email accounts. Thunderbird checks both my accounts every 10mins. However, until today the simplest way to manually check my multiple accounts was to click the arrow to the right of the large "Get Mail" button and choose "Get all new messages" from the drop-down box. A two click operation!

Today, I found Easy Get Mail. Easy Get Mail makes account checking context-sensitive.

Formerly, pressing the Get Mail button would check email only for the selected account. After the installation of Easy Get Mail, pressing Get Mail will check the email for all accounts, unless an account root folder is selected in the folder pane, in which case only the selected account will be checked.

Windows XP Pro - tips and tweaks

2006-01-14T10:36:00.000Z

NTFS

One thing you may consider doing is converting your filesystem to NTFS. By default, most computers ship hard drives formatted for the FAT32 filesystem. This was largely superceded by NTFS, introduced with Windows NT. The primary advantages of NTFS over FAT32 are:

Much stronger security model - with FAT32 every user has complete access to the filesystem, whereas NTFS permissions are more UNIX-like.
Better performance for large volumes.
Support for encryption and compression.
NTFS is a journalling filesystem. All transactions are logged, which facilitates recovery after crashes. The practical upshot is that you won't be forced to run Scandisk each time your computer crashes!

NTFS has some disadvantages. It may lead to slower performance on small volumes (say less that 8Gb). You may also have difficulties working with NTFS from other operating systems. At the moment, there is no way to write to an NTFS drive from within Linux. At any rate, I considered the advantages to outweigh the disadvantages and decided to perform the conversion. The procedure is for conversion is given at the Microsoft support site.

Simple Sharing

If you want to be able to view and change the permissions of objects within Windows, you would be well advised to turn off simple sharing. To do this, go to:

Start → Control Panel → Administrative Tools → Local Security Policy

Then go to

Security Settings → Local Policies → Security Options

Choose Network Options. Find the key "Network Access: Sharing and security model for local accounts". Change the setting to "Classic - local users authenicate as themselves".

ClearType

ClearType is a mechanism for producing high quality display on LCD screens, such as those found in laptops and flat panel displays. By default, ClearType is deactivated in Windows XP, but it is highly recommended that you turn it on! To activate ClearType, simply right-click on the desktop and select the Properties option from the context menu. In the Appearance tab, choose Effects..., and then choose the ClearType option for "Use the following method to smooth edges of screen fonts". In order to more finely tune ClearType, download and install the ClearType PowerToy. ClearType can then be tuned from Control Panel → Appearance and Themes → ClearType Tuning.

Tweaking the Acer - Part III, ePowerManagement continued

2006-01-13T11:01:00.000Z

In Part II, we discussed how to get Acer ePowerManagement working for ordinary non-privileged users. Well, half-working at least. To go the extra distance, we need to make further changes. As well as the "Access denied" messages, you may also find that ePowerManagement stops if you log out and doesn't restart when you log in again. To fix these problems, we'll give the user the ability to start and stop the service at will, and then write a script to perform these operations.

First, you need to download subinacl from the Microsoft website. Having done this, run the following command:

subinacl /service epowermanagement /grant=billybob=STOP

where billybob is your username. This gives billybob the right to query, start, stop, and pause/continue the service.

Go back to the Service configuration tool. Right-click on epowermanagement and select properties. Change the Startup type to Manual. This means that the service won't be started automatically on bootup, but will be started only when called upon.

Now we need to write a script which will call the service. Create a file epm.bat in your home directory (or wherever). Type the following into the file:

@echo off
%windir%\system32\sc.exe stop epowermanagement
%windir%\system32\sc.exe start epowermanagement

Copy this file in your Startup folder. The simplest way to do this is to first copy the icon for epm.bat, then right-click on the start menu button and choose open. Navigate to the Startup folder and paste the file. This should do the trick, though you may want to log out and log back in again to get the full effect.

For further information on running applications as a non-privileged user, read the non-admin wiki, and Aaron Margosis' Weblog.

Tweaking the Acer - Part II, ePowerManagement

2006-01-12T09:21:00.000Z

One of the much touted features of the Intel Pentium M series is their ability to dynamically change processor speed in response to software demands. The upshot of this is that a laptop can 'run idle' when not connected to AC power, extending battery life. Windows XP supports SpeedStep and other power management features, but Acer provides its customers with a more advanced tool, called Acer ePowerManagement. Unfortunately, as with many Windows applications, ePowerManagement only works if the logged-in user has administrator privileges.

In UNIX, the obvious solution would be to set the SUID bit on the relevant application, but Windows has no equivalent concept, so I had to try a different avenue.

My plan was to run Acer ePowerManagement as a service. First, I downloaded the Windows server 2003 resource kit tools. I then created a service called epowermanagement by typing the following at the command prompt:

cd "C:\Program Files\Windows Resource Kits\Tools"
instsrv.exe epowermanagement "C:\Program Files\Windows Resource Kits\Tools\srvany.exe"

The service can be configured by going to

Start → Control Panel → Administrative Tools → Services

and then finding epowermanagement. Right-click for the context menu, and select properties. From the "log on" tab, select Local Account and check "Allow service to interact with desktop". In order to set the actual application to run, one needs to use regedit.

Go to

HKEY_LM\SYSTEM\CurrentControlSet\Services\epowermanagement

(where LM is short for LOCAL_MACHINE) and create a new key called Parameters. In this key create a new string, and call it Application. I changed its value to C:\Acer\ePM\EPM-DM.exe.

This is enough for most purposes, but as it is, you will see error messages of the form "Access violation at address xxxxx in module 'ePM.exe'" when connecting/disconnecting from AC power. Moreover, you will only be able to alter the settings when logged in as an Administrator. The resolution of these problems will be the topic of Tweaking the Acer - Part III.

Tweaking the Acer

2006-01-11T11:31:00.000Z

In 2005, I bought an Acer Travelmate 4151LMi laptop (part number LX.T7606.068). It's a nice machine and more than adequate for my tasks (i.e. surfing and editing web pages, reading email, editing maths documents with LaTeX, and general word processing). The graphics subsystem (onboard Intel 915GM) is not fantastic, so I wouldn't recommend it if you are a serious gamer. Note also that the graphics system has no memory of its own and borrows 128Mb from the main memory.

To start with, I had some problems with choppy DVD playback, a good deal of noise, and generally slow performance. Ultimately, I found that the root cause was in a piece of software called Acer eRecovery, in particular, a subprogram called Monitor.exe. I disabled the software by starting regedit and editing the following key:

HKLM\Software\Microsoft\Windows\CurrentVersion\Run

From this key, I removed the value name eRecoveryService which has value data C:\Windows\System32\Check.exe

Et volia! The performance suddenly shot up, the DVD playback became smooth and the noise disappeared — in fact, the laptop is very quiet. Reading the blog of Crippled Canary, it seems that the problem is due to the fact that eRecovery uses the D: partition, which must be of type FAT32. This will cause problems if you have a dual-boot system.

Cygwin

2006-01-09T17:30:00.000Z

By nature, I'm a Linux man. My dalliance with Microsoft ended at Windows 95 after I discovered the beauty and power of Linux and it's command shell. Unfortunately, Linux suffers from poor hardware support, and the purchase of a new laptop in 2005 forced my hand. I couldn't install Ubuntu (Hoary Hedgehog) as the installer didn't recognise my spanking new SATA DVD drive. I managed to install Debian on the system, but found that it didn't properly support some of the newer hardware in my laptop; notably lacking was xv support for the graphics card.

I had a busy time ahead of me and didn't want to waste it recompiling the kernel and patching drivers. Since I knew Windows XP would be able to make best use of the hardware without having to edit a configuration file, I bit the bullet and ditched Linux in favour of the Redmond OS.

Not willing to completely give up on my penguin fix, I looked into Cygwin, a Linux emulator for Windows. In a previous incarnation, I had known Cygwin as a console-based emulator, and had used it to port a Connect4-style game to Windows. However, since 2001, Cygwin has shipped with a port of the X Window System. Essentially, Cygwin allows the user to have a Linux desktop environment running on top of Microsoft Windows.

At the time of writing, there exist beta ports of GNOME 1.4 and KDE up to version 3.1.4. However, I plumped for speed and stability over a fancy desktop and went with fvwm2. This window manager needs a bit of "config file editing", but I had a ready-to-go config file from my University account. A beginner may be better off with WindowMaker, which also comes with Cygwin.

In later articles, I'll write about my experiences configuring Cygwin for LaTeX, sshd, rsync, etc.

Elementary Wavelet Analysis

2005-12-29T17:52:00.000Z

This is the abstract for my MSci thesis on wavelet analysis. For the full article, see my main site.

Abstract: A discussion of orthonormal wavelet bases and wavelet
series, utilising the notion of multiresolution approximations. I start by discussing multiresolution approximations and show how to find an orthonormal basis of the generating space, consisting of translates of a `scaling function' φ. The notion of orthornormal wavelet bases is then introduced, and it is shown how one can go from a multiresolution approximation to a wavelet basis with a scaling function, and vice-versa. The article then turns to the description of wavelet bases of compact support and multi-dimensional wavelet bases (using the tensor product method). Finally, the regular wavelets of compact support are seen to form an unconditional basis of the space H¹(Rⁿ) of Stein and Weiss, this being an interesting subspace of L¹(Rⁿ).

This is my MSci project, which I undertook in the fourth year of my undergraduate degree at Imperial College, London. It is concerned with mathematical entities known as wavelets, and uses the wavelets to investigate a space called H¹(Rⁿ).

Though the title of the project is 'Elementary' wavelet analysis, you still do need to know some maths to understand it! In particular, you should be aquainted with undergraduate functional analysis. If you'd prefer something less technical, why don't you try The Engineers Ultimate Guide to Wavelet Analysis. This Internet article was written by a non-mathematician and designed for non-mathematicians, so anyone (well any scientist or engineer) should find it quite accessible. If you want to read more on the topic, then another not-so-technical resource is G. Kaiser, A Friendly Guide to Wavelets, Birkhauser, Boston 1994. A good introductory volume for the more mathematically minded amongst you is C. K. Chui, An Introduction to Wavelets, Academic Press Inc., New York, 1992. But the book I referred to mostly whilst writing my project was Y. Meyer, Wavelets and operators, Cambridge University Press, Cambridge, 1992. It's a pretty tough going book and I wouldn't recommend it unless you're really up to scratch on your real analysis; nonetheless it is required reading if you seriously want to understand the deeper theoretical foundations of the wavelet theory.

In case you meet the above requirement and are interested in reading further, you might first like to know a little about what wavelets are and how they can be used.

A one-dimensional wavelet basis is a basis of L²(R) (depending upon the author, the basis may or may not be required to be orthonormal) and equally an n-dimensional wavelet basis is a basis of L²(Rⁿ), in much the same manner the complex exponentials form an orthonormal basis of L²(0,2π). So indeed wavelet analysis shares some similarities with Fourier analysis. However if you read the article, you'll find that wavelets really kick arse, compared with Fourier analysis.

GnuPG and Friends

2005-12-29T15:14:00.000Z

Installation of GnuPG

GnuPG is the GNU Privacy Guard — an open source replacement for PGP. GnuPG can be used for encrypting and/or signing emails and other documents.

I'm going to describe the process of setting up GnuPG with Microsoft Windows XP. Another short guide is to be found on mozdeg.org. The canonical reference is the Gnu Privacy Handbook.

First you need to download a copy of GnuPG, verify its authenticy, then install it. The instructions for so doing are to be found on the GnuPG website.

Having installed the software, I recommend adding GnuPG to your %PATH% environment variable. To do this, right-click on "My Computer", select Properties, then Advanced, then environment Variables. Add (if it doesn't exist) or Edit (if it does), the User Variable "PATH". Add the value C:\Program Files\GNU\GnuPG. You may now access gpg from the command line.

Your personal data will be stored in %APPDATA%\gnupg. Typically, if your username is Bob, the personal data will be stored in C:\Documents and Settings\Bob\Application Data\gnupg.

If you already have some keys from another installation of GnuPG (which will be found in files called secring.gpg and pubring.gpg), you may import them with gpg --import filename.

If you don't already have your own keys, you'll have to generate them with the command gpg --gen-key. Follow the instructions. I recommend generating a key-pair which doesn't expire, though this can be changed later. Make your passphrase fairly long!

Keyservers

Your key is useless unless you can share it with others. One way to share your key is to use a keyserver. First find the keyID of your public key with gpg --list-keys. The keyID is an
8-digit hexadecimal number. The keyID for one of my public keys is CC144DA2. We'll use this in the following examples.

Before sending the key to a server, it's a good idea to create a revocation certificate. You'll need this if your key is every compromised. The revocation certificate is used to inform a server that the key has been revoked. The syntax for the creation of a revocation certificate is gpg -a --output filename --gen-revoke CC144DA2.

We may now add our public key to a key server. Here is the command:
gpg --send-keys --keyserver pgp.mit.edu CC144DA2

Enigmail

Now we need to do something useful with GnuPG! I assume you're using the Thunderbird/Mozilla email client. Find and install the enigmail extension. The only setup required is to tell enigmail where to find GnuPG. Close down and restart Thunderbird (if you haven't done so already). Loacte the OpenPGP menu and select Preferences. For the GnuPG executable path, enter C:\Program Files\GNU\GnuPG\gpg.exe. It should be fairly clear how to
operate Enigmail.

Fingerprints; the Web of Trust

I mentioned that a key pair is only useful if the public key is shared. However, you need to ascertain that a key you find (from a keyserver, for example) really does belong to the person it claims to. This is where fingerprints enter the picture.

Each key has a fingerprint associated with it. If you download a key, you can contact the key's owner in person to find out the key's fingerprint. If the fingerprints match, you can be almost certain that you have found a valid key. You can find the fingerprint of a key by entering gpg --fingerprint keyID. Once you are certain of the authenticity of a key, you may sign it with your own secret key. Having signed the key, you may send the updated key to a keyserver (note, you will be sending someone else's key to the keyserver!).

Anyone who subsequently downloads the key from the server will see that you have placed your seal of approval on the key. If they have a validated copy of your key, this may give them some level of confidence that the key is authentic, without having to check the fingerprint themselves. In fact, GnuPG has a built-in system called the web of trust which automates this process to some extent.

For more information on these issues, please refer to the GNU Privacy Handbook.

First Day

2005-12-29T14:49:00.000Z

Having spent almost nine years surfing the web, this is my first foray into the world of blogging. It remains to be seen what I intend to do with this site, but I hope it will be of some interest!

In the meantime, I'll point to some of the work on my main website. I have a discussion of cryptography, focusing on the RSA code; it is interactive and allows one to encode and decode text messages with the RSA algorithm. I also have a page on partial fractions, which I hope will be useful to advanced high-school students who want a more thorough understanding of this topic.