Changing The Gas Meter, Part 2

Following a failed attempt by British Gas to have my meter changed, I received some paperwork from National Grid. They want to charge me £110.65 to replace the door on the meter box. I reckon it can wait. In the meantime, I'll investigate with British Gas to find out why they want to change the meter in the first place.

Changing The Gas Meter, Part 1

A few weeks ago, I received a letter from Siemens Metering Services saying that they had been tasked by British Gas to change my gas meter and that they had provisionally booked an appointment for today, between 8:00 and 20:00. I then arranged to be working from home today and called Siemens to confirm that the date was fine and that they were welcome to come and change the meter. Unfortunately, they couldn't give me a more precise time so I made sure I could spend the whole day at home, waiting for an engineer.

The Siemens engineer arrived shortly after lunch, which I was rather pleased with, and proceeded to find out which of the three meters mine was. It took him a minute or two, after which he looked at me and said:

The covering box your meter is in is broken so I'm not allowed to change it, the box needs to be changed first.

Indeed, the box in question is missing its door and has been missing that door since before I purchased the flat. Considering this is not a completely unusual occurrence as I can spot a few meters in my street that have a damaged box, my neighbour to start with, and the engineer confirmed this was common, you'd have thought that, in all their wisdom, Siemens could have mentioned in the letter they sent me that their engineers could only change the meter if the box was intact? Had I known, I would have checked and told them when I confirmed the appointment that the box needed changing, we could have organised the change immediately and it would have saved everybody a good deal of time and effort. But no, that would have been too easy! Of course, what makes it even more complicated is that it won't be the same company that changes the box. So I'll have to sort that out, work from home the day they change the box, re-organise the meter change, work from home that day again and finally I may have a new meter. The fact that I never asked the meter to be changed in the first place, and that I have no idea why British Gas feel they have to change it at all, means that I am of course extremely motivated to do all that and not at all annoyed by it.

The silver lining in all that is that the Siemens engineer was a very nice guy and said he would organise the paperwork to do the box change to be mailed to me. So Siemens may be useless in their written communication but at least the guys they send out to do the work are nice and sensible. That's half the customer service done properly. Well, we'll see if and when I have the promised paperwork.

Tuning a Wi-Fi Router with Linux

Nowadays, with Wi-Fi broadband routers becoming the de-facto standard in the home, comes a new problem for people who live in cities: interferences between neighbouring wireless networks. This can lead to slow connections or even dropped connections. A few years ago it was not a problem, few people had Wi-Fi routers at home and if you had one your router would work great out of the box. Nowadays, everybody's got a Wi-Fi router at home, whether it be a traditional router or a phone that masquerades as one. Wi-Fi was designed to avoid interferences by being able to work on a number of frequencies and every single router allows you to choose what frequency to use by selecting a channel. In the UK, you will typically have the choice of a channel value between 1 and 13. Just go to the wireless settings area of your router administration page and you should be able to change the channel, as shown on this example from a Netgear router:

Netgear wireless settings screen, set to Channel 4

That's simple: change the value, ensure it's applied and, depending on the manufacturer, reboot the router. But what is a good value that will ensure a good connection? Well, it depends on your environment. As you want to avoid interferences, this value should be as far as possible from other routers in the range of your equipment. But how do you tell what channel other routers in your area use? The Linux wireless tools come to the rescue, and in particular the one called iwlist. If you have a Wi-Fi laptop running Linux, it will have this utility installed as standard. The basic command we want is:

$ iwlist [interface] scan[ning]

To do a full scan, we need to run it as root so we'll prepend sudo to it. It is not necessary to specify a network interface but you might as well do so to avoid scanning non-wireless adapters. On my laptop, the wireless interface is eth1 so here is what I obtain by running iwlist against it:

$ sudo iwlist eth1 scan
eth1      Scan completed :
          Cell 01 - Address: 02:1D:68:4B:6D:F6
                    ESSID:"BTOpenzone"
                    Protocol:IEEE 802.11bg
                    Mode:Master
                    Frequency:2.412 GHz (Channel 1)
                    Encryption key:off
                    Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 6 Mb/s; 9 Mb/s
                              11 Mb/s; 12 Mb/s; 18 Mb/s; 24 Mb/s; 36 Mb/s
                              48 Mb/s; 54 Mb/s
                    Quality=27/100  Signal level=-83 dBm  
                    Extra: Last beacon: 240ms ago
          Cell 02 - Address: 00:1D:68:4B:6D:F5
                    ESSID:"BTHomeHub-954D"
                    Protocol:IEEE 802.11bg
                    Mode:Master
                    Frequency:2.412 GHz (Channel 1)
                    Encryption key:on
                    Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 6 Mb/s; 9 Mb/s
                              11 Mb/s; 12 Mb/s; 18 Mb/s; 24 Mb/s; 36 Mb/s
                              48 Mb/s; 54 Mb/s
                    Quality=29/100  Signal level=-82 dBm  
                    Extra: Last beacon: 248ms ago

... and so on

Each Cell section provides the details of a wireless hub in range. For each of them, the line we are interested in is the one that start with the word Frequency. So, if we use grep to filter the data, we get:

$ sudo iwlist eth1 scan | grep Frequency
Frequency:2.412 GHz (Channel 1)
Frequency:2.412 GHz (Channel 1)
Frequency:2.412 GHz (Channel 1)
Frequency:2.427 GHz (Channel 4)
Frequency:2.442 GHz (Channel 7)
Frequency:2.442 GHz (Channel 7)
Frequency:2.462 GHz (Channel 11)
Frequency:2.442 GHz (Channel 7)

This shows that I am in range of 8 wireless hubs. The one I am using is the fourth one, set to use channel 4. But that's because I changed it yesterday. It used to be configured with its default setting, using channel 11, which was clashing with the one before last. In fact, running the command at different times, it appears that all routers in my area use channels 1, 7 or 11. With a possible set of channels between 1 and 13, there are 5 unused channels between 1 and 7, 3 between 7 and 11 and 2 above 11. So the best choice is halfway between 1 and 7: channel 4. And since I reconfigured the router to use that channel, speed has improved significantly and dropped connections have been a thing of the past.

Now, why router manufacturers don't design their products to be able to scan neighbouring wireless networks at start-up and choose a frequency that doesn't clash with other hubs, I don't know. By any means, leave the ability to power users to explicitly specify the channel but a little bit of automation would go a long way in making Wi-Fi easier for the average home user.

Update

After all this, I had to change the router's channel again earlier, as more access points were switched on during the evening. At one point, a full scan showed a grand total of 24 wireless networks! So I changed my router to channel 13 and it all seems fine so far. Methinks I'll have to do something about improving the range of that router. While I was at it, I also upgraded the firmware so we'll see if it makes a difference.

Parcel Delivered on Time Shocker!

I was expecting a parcel delivered today. As usual I was quoted a delivery time of between 8am and 6pm, which meant I was stuck at home until it arrived. I was fully expecting to wait all day, make several calls to the courier company and not get the goods delivered today, as has happened several times in the past and as recounted by Toastboy and Coofer Cat. But how wrong I was: the parcel was delivered before 10am by a courteous and smiling driver!

So credit where credit is due: well done DPD, it was perfect and I shall feed this back to the supplier.

Canon and Linux, part 3

For the background to this post, see part 1 and part 2.

I got an answer from Canon on Tuesday:

Dear Customer,

Thank you for your query regarding the Firmware update for your EOS 5D.

As the versions available for download are only compatible with Windows and Mac, we could produce a zipped up version of the .FIR file so that you can update your firmware on your Linux computer.

Please note that whilst we try our best to ensure the file we provide you with is virus free, you must install the firmware entirely at your own risk.

Could you please also confirm that you have an EOS 5D.

Some progress then. However, they ask me some more questions, to which I can give the answers but you can't reply directly to their support email address, you have to go through the standard form on the web site again. I did that and asked the following question:

Dear support,

Yes, I can confirm that I have an EOS 5D and I am happy to update the firmware at my own risks. Have Canon got any plans to offer a zip version of the firmware in the future in order to support all their customers equally?

So now I'm waiting for the next answer. This whole malarkey of going through the web form every time means that there are potentially 2 to 3 business days delay for the answer to each new question even if it relates to the same problem, which can potentially drag things out a lot, especially considering the web form is limited to 4000 characters!

Small Plastic Bag Madness

Following a push to eradicate the plastic bag from the United Kingdom (and London in particular), supermarkets have stopped giving the standard plastic carrier bags unless you ask for them. And even then, a lot of shops will now preferably give you a small plastic bag rather than a normal size one. On the face of it, this all sounds like a good idea as it consumes less plastic but it only looks at the very beginning of the life of a plastic bag and assumes I will throw it away once I get home. Well, no, I don't throw my plastic bags away: I reuse them. There are tons of different ways I can reuse a standard size supermarket plastic bag: as a bin liner for my kitchen bin for instance. But what can I do with the small ones they now give away? Not much! So they pile up at home. It's even got to the point where I started wondering if I needed to buy plastic bin liners for the kitchen bin as I'm now running out of standard size plastic bags!

So what could be the solution to this conundrum? Most people have two reasons to go to the supermarket: either to do a weekly food shop, in which case they will need large bags and are even quite likely these days to have their own bags, so no problem there; or they will just pop in to buy a few items that they realised they needed, in which case they may need a small bag. In that last case, it seems to me that the small plastic bag is not the right answer. A small (recycled) paper bag, similar to the ones you get in Pret or most other sandwich shop would be perfect! When I come home, I can then pop the small paper bag in my recycling green box and be done with it: much nicer and easier than dealing with a small plastic bag that is difficult to recycle or reuse.

Stop this small plastic bag madness!

Canon and Linux, part 2

5 days ago, I sent a complaint email to Canon about their lack of support for Linux (or any operating system other than Microsoft Windows or Apple OS-X) when it comes to upgrading the firmware of my camera. I received this standard email reply today:

Dear Customer,

Thank you for your recent enquiry regarding your Canon product.

Your query has been sent to the appropriate group and is currently under investigation.

Yours sincerely,

Canon Support Centre

Should our answer not fully resolve your problem, please feel free to either re-submit a new query by clicking here, or alternatively call our support helpdesk at 08705 143 723 Monday to Friday from 9:00AM to 5:30PM stating the 7 digit reference number in the subject of this email.

We aim to answer queries as soon as possible. Responses on average take 2 to 3 business days (or the next working day if submitting on a weekend or public holiday).

If I read between the lines, it looks like the Christmas period was out of hours so the average of 2 to 3 business days probably starts now.

Canon and Linux

I've now been the proud owner of a Canon EOS 5D for a few years. I've never upgraded the firmware on it but tonight I thought I would investigate how complicated it was. I easily found the corresponding web page on the Canon web site. It seems easy enough: you get a .fir file that you put in the root directory of a newly formatted memory card and you then follow the upgrade procedure on the camera. All easy and simple. The only snag is that you get two version of the firmware package: a self-extracting .exe file for Windows or a .dmg package file for Mac OS-X. Both those options are proprietary so they don't work on Linux. Therefore, there is no way I can upgrade my firmware using my laptop. I could use the Mac desktop at home but I am not home right now. Furthermore, it's not even a software problem, it's just a packaging problem: there is nothing in the .exe or the .dmg apart from the automated unpacking. It would be so easy for Canon to offer a simple .zip file that can be extracted on any operating system. By any means, provide the proprietary formats for people who will benefit from them but also provide a generic format that can be used anywhere. So here is the complaint I registered on the Canon UK support site:

You offer firmware download on the Japanese site (http://web.canon.jp/imaging/eos5d/eos5d_firmware-e.html). Unfortunately, you only provide proprietary Windows and Mac packages. Using a Linux laptop, I cannot use those formats. If you were to offer a simple ZIP file for all other operating systems, it would enable all your users to update their firmware. As such, I feel treated like a second class citizen by Canon and it is very disappointing. I am happy to take complete responsibility for updating the firmware from a Linux machine but I would like to be given the option. Is there any way I can download a version of the latest firmware that can be extracted on Linux? If yes I would appreciate if you could provide me with the details of such a download.

We shall see if anything comes out of it. They promised to come back to me within 2 to 3 days. Then I went and filed a second complaint because their web site crashes when I try to log into it as a registered Canon customer but that's a whole different story.

Fractals with Octave: Classic Mandelbrot and Julia

After reading this article in FSM, I decided to have a go at doing fractal images with Octave. In the process, I discovered quite a bit about fractals so here is the result of those experiments. First I'll build some classic Mandelbrot and Julia fractal images.

Pre-Requisites

All the code below was created on Ubuntu using Octave. If you don't use Ubuntu, check with your distribution or follow the instructions on the Octave web site. If you have Ubuntu, you just need to install the Octave package. To do this, open a terminal and type the following at the command line:

$ sudo apt-get install octave

Alternatively, considering that Octave is meant to be compatible with MATLAB, it should be possible to adapt everything in this series to MATLAB.

Fractal Basics

Fractals is a term that encompasses a variety of mathematical constructions that all have a property in common: they are inherently recursive. This means that you can only ever produce an approximation of a fractal to a given level of precision, which is why their study is well adapted to computational approximation methods, what a computer is inherently designed for.

Mandelbrot and Julia sets are generated as a result of studying the convergence properties of series in the complex plane. The series that is most commonly used is:

z_n+1=z_n²+c

This series converges or diverges for large values of n, depending on the value of z₀ and c. All well and good but how does that help us produce cool fractal images with Octave? We're getting there.

The Julia and Mandelbrot sets

The Julia sets (from Gaston Julia who first studied such series) show the behaviour of complex series when you vary the value of z₀ in the complex plane, for a given value of c. But the question is then: what are interesting values of c?

Conversely, the Mandelbrot sets (from Benoît Mandelbrot who first used a computer to study such series) show the behaviour of the same series when you vary the value of c in the complex plane, for a given value of z₀, the most classic example using z₀=0.

Constructing an Image

So, if we map the pixels of our image to the complex plane, we can associate a value of c to each pixel and calculates values of z_n for z₀=0 in order to obtain a Mandelbrot image.

But what values of n are we interested in and what do we do with the value we calculate? As said above, we are interested in whether the series diverges or not so we could colour a pixel in white if it diverges and in black if it converges.

How do we know whether the series converges or diverges then? Some people much smarter than I am have proven that for a given polynomial series, there exists a value r such that if for any n, |z_n|>r, then the series diverges. For the polynomial given above, r=2.

So now, we can identify for each point whether the series diverges or converges so we can colour the corresponding pixel white or black. But most Mandelbrot images you see in the wild are not black and white, they are rather colourful: so how do they get all their funky colours? Each colour is associated with how quickly the series diverges. To obtain that effect, we will associate the value 0 with points that converge and a number greater than 0 for points that diverge. That number will be the lowest value of n for which |z_n|>r. Each value will then be associated to a colour in a colour to produce the final image.

The Code

After all this background, it's time to do some coding. But first, we need to ensure that Octave knows where to find the functions we will define. The way Octave works, it looks for function files in its path and expects each function to be stored in a file of the same name with the .m suffix. By default, the Octave path doesn't include any directory for which you have write access so what I did was to create an octave directory in my home directory as well as a .octaverc file that adds ~/octave to the path:

.octaverc

addpath("~/octave");

From now on, every .m file in the ~/octave directory will be found by Octave and recognised as a function file. You will need to restart Octave for this to take effect.

Now that the preamble is out of the way, we can start coding in earnest so let's fire a trusty file editor and create a file called mandelbrot.m in the ~/octave directory. In this file, we are going to define a mandelbrot function that takes 4 arguments: cmin, cmax, hpx and niter, corresponding respectively to the minimum and maximum values of c, the number of horizontal pixels in the image and the number of iterations:

function M=mandelbrot(cmin,cmax,hpx,niter)

The aim of this function will be to populate the matrix M with the colour values of pixels. The first thing we do is calculate the vertical number of pixels such that ratio of the final picture is the same as the one given implicitly by cmin and cmax:

vpx=round(hpx*abs(imag(cmax-cmin)/real(cmax-cmin)));

We then initialise z, c and M. z and M are easy as they just need to be initialised to zeroes. However, note that the vertical dimension is the first one because Octave orders a matrix per columns first. c is a bit more complicated as it need to be initialised to a matrix that is vpx by hpx in size with real values spread along the horizontal axis and imaginary values spread along the vertical axis. The linspace function produces a vector of values evenly spread between the minimum and maximum across the given number of points. The meshgrid function then produces 2 real matrices out of those 2 vectors that are then merged together as a complex matrix.

z=zeros(vpx,hpx);
[cRe,cIm]=meshgrid(linspace(real(cmin),real(cmax),hpx),
                   linspace(imag(cmin),imag(cmax),vpx));
c=cRe+i*cIm;
M=zeros(vpx,hpx);

The final part of the function is the main loop. Here we use Octave's full potential using matrix calculation and a matrix mask. The mask is calculated so that it contains all the points that have not yet diverged and the corresponding entries in the result matrix are incremented. Points that diverge are not incremented and are excluded from the next calculation. Finally, we set the remaining points, that is the ones that haven't diverged after niter iterations, to 0.

for s=1:niter
  mask=abs(z)<2;
  M(mask)=M(mask)+1;
  z(mask)=z(mask).^2+c(mask);
endfor
M(mask)=0;

Putting it all together, here is the final file:

mandelbrot.m

function M=mandelbrot(cmin,cmax,hpx,niter)
  vpx=round(hpx*abs(imag(cmax-cmin)/real(cmax-cmin)));
  z=zeros(vpx,hpx);
  [cRe,cIm]=meshgrid(linspace(real(cmin),real(cmax),hpx),
                     linspace(imag(cmin),imag(cmax),vpx));
  c=cRe+i*cIm;
  M=zeros(vpx,hpx);
  for s=1:niter
    mask=abs(z)<2;
    M(mask)=M(mask)+1;
    z(mask)=z(mask).^2+c(mask);
  endfor
  M(mask)=0;
endfunction

So let's run it to see what comes out of it:

octave-3.0.1:1> Mc=mandelbrot(-2.1+1.05i,0.7-1.05i,640,64);
octave-3.0.1:2> imagesc(Mc)

Octave should then fire up Gnuplot and show a nice classic Mandelbrot set:

Classic Mandelbrot Set

Following this success, let's tackle the Julia set. The code should be very similar, with the exception that c should be a parameter of the function and z is the variable that needs initialisation using linspace and meshgrid. Furthermore, c doesn't need to be masked in the loop because it is a scalar value, not a matrix. So without further ado, here's the code for the ~octave/julia.m file:

julia.m

function M=julia(zmin,zmax,hpx,niter,c)
  vpx=round(hpx*abs(imag(zmax-zmin)/real(zmax-zmin)));
  [zRe,zIm]=meshgrid(linspace(real(zmin),real(zmax),hpx),
                     linspace(imag(zmin),imag(zmax),vpx));
  z=zRe+i*zIm;
  M=zeros(vpx,hpx);
  for s=1:niter
    mask=abs(z)<2;
    M(mask)=M(mask)+1;
    z(mask)=z(mask).^2+c;
  endfor
  M(mask)=0;
endfunction

Let's choose a value for c that corresponds to a point at the limit of convergence in the Mandelbrot set, such as -0.75+0.2i, and call the julia function:

octave-3.0.1:3> Jc1=julia(-1.6+1.2i,1.6-1.2i,640,64,-0.75+0.2i);
octave-3.0.1:4> imagesc(Jc1)

Octave should then refresh the Gnuplot windows and show the result:

Classic Julia Set for c=-0.75+0.2i

Factorising Code

Considering both function are so similar, it should be possible to factorise code between them and have a core Mandelbrot/Julia function called by two simpler functions. The major difference is in the initialisation before the loop so can we factorise the loop? The only difference in the loop between the two functions is that in the mandelbrot function, c is masked because it is a matrix, whereas in the julia function, it is is not masked because it is a scalar. The solution is to transform c into a matrix of identical values in the julia function. We now have three files: mjcore.m that contains the core code and refactored mandelbrot.m and julia.m. Here is the full listing:

mjcore.m

function M=mjcore(z,c,niter)
  M=zeros(length(z(:,1)),length(z(1,:)));
  for s=1:niter
    mask=abs(z)<2;
    M(mask)=M(mask)+1;
    z(mask)=z(mask).^2+c(mask);
  endfor
  M(mask)=0;
endfunction

mandelbrot.m

function M=mandelbrot(cmin,cmax,hpx,niter)
  vpx=round(hpx*abs(imag(cmax-cmin)/real(cmax-cmin)));
  z=zeros(vpx,hpx);
  [cRe,cIm]=meshgrid(linspace(real(cmin),real(cmax),hpx),
                     linspace(imag(cmin),imag(cmax),vpx));
  c=cRe+i*cIm;
  M=mjcore(z,c,niter);
endfunction

julia.m

function M=julia(zmin,zmax,hpx,niter,c)
  vpx=round(hpx*abs(imag(zmax-zmin)/real(zmax-zmin)));
  [zRe,zIm]=meshgrid(linspace(real(zmin),real(zmax),hpx),
                     linspace(imag(zmin),imag(zmax),vpx));
  z=zRe+i*zIm;
  cc=zeros(vpx,hpx)+c;
  M=mjcore(z,cc,niter);
endfunction

Next

In the next article of this series, More on the Classic Sets, we wander around the Mandelbrot and Julia sets and see what happens to the Mandelbrot set when we choose a value for z₀ that is different from 0. I also demonstrate how to save images to disk and talk about colour maps.

Wandering Ibex

After 6 weeks with Ubuntu 8.10, aka Intrepid Ibex, the change that has most affected the way I use my laptop is the new network manager. Connecting to a wireless network is easy and just works. It is generally fast to connect, definitely faster than with 8.04 aka Hardy Heron. It will immediately recognise networks it knows about and connect automatically. In particular, it is much better than Windows at connecting to a Wi-Fi network that does not advertise its SSID and recognising it later as a known network.

But the biggest benefit is the support for 3G modems out of the box, in particular the Huawei models available in the UK. When I plugged in my 3 USB modem for the first time, it recognised the device, asked me what country and what operator I was on and that was all the configuration I had to go through: no software to install, instantly on. It also integrates seamlessly into the network manager so there's no flaky third party software to use every time I want to connect. I just have to plug the modem in, select it in the network manager drop down and hey presto, in a few seconds I am online, whether in a pub, on the train or anywhere I've got network coverage from 3 (which is sometimes a bit patchy, I have to admit). OK, there's one thing it doesn't do, which the Windows version does: it doesn't tell me how much of my monthly quota I've consumed. However, I very rarely download large files via the modem so I've never reached the limit: large files is what the (fast) home broadband is for. It would be more important for someone who does use a 3G modem more heavily than I do. Maybe that's a feature to ask for in the next version?