Tab vs space

I was using tab for indentation in coding, instead of spaces. Because I feel that one byte of tab is better than four bytes of space. It produces smaller file size.

However, the problems become prominent in the following circumstances.

• Viewing different languages may require different indentation width. XML and HTML may use 2 characters width, other languages may use 4 characters width. Changing the tab width from the setting frequently is inconvenient.
• Editing source code with different developers and using different text editors will produce source code with both tab and space indentation. As a result, the indentation becomes inconsistent.
• Emacs problem. If the Emacs tab width is set to 8 characters, but the source code indentation is 4, this produces both tab and space indentation at the same line, for example, 3 indents (12 characters width) produce 1 tab with 4 spaces. Oh dear, I always show the whitespace and tab marks in the editor. The ugliness disturbs me.
• Git diff view. If using Git GUI, it will highlight the tab indentation when the pervious line is a space indentation.

So, in the cases above, space indentation becomes handy. Though different developers use different text editor may produce different width of space indentation, with space indentation will produce better output than tab indentation.

But not all text editors support auto-indent feature, and not all text editors support tab to space indentation. So, I have to choose the text editor that meets my need.

I use jEdit and recently use Emacs. jEdit allows to convert the tab to space easily. But jEdit does not have the fixed indentation like Emacs. Emacs has the “major modes”, based on the major modes, the source codes are syntax highlighted differently and the indentation will be arranged differently.

Just a short comparison between Emacs and Atom Text Editor. Emacs is a very old text editor; Atom is modern. Both are highly customisable. Atom has a lot of packages available; Emacs has more than enough packages available. But I choose Emacs over modern editor like Atom, because Emacs has various powerful modes available. It is not only an editor, but can also be a debugger, or even IDE. Based on my experience, Emacs auto-indentation on the complex HTML with JavaScript and CSS works better than Atom.

As a result, I choose space indentation over tab indentation, as it is more consistent and text editor independent.

Ubuntu with BCM43228

 

My campus lab has the Dell desktops. I am not sure the model, but the network devices are Broadcom BCM43228. As a result, after installation of the Ubuntu (they were not installed by me), Ubuntu cannot get WiFi connection to online.

Since my student mentioned that Windows can use the ethernet cable to share the wireless network, I asked him to help to share the wireless network from Windows on the other Dell desktop, and connect to the target Dell desktop.

This step works.

Next, I followed this Q and A post, just followed exactly all the commands there. Then reboot.

Yes! It works. Now, my students can test Ubuntu.

Statistics and functional programming languages

Recently, I feel fervent to learn functional programming, because i) (in my opinion), it will become a trend, and ii) the interpreter can be used as an advanced calculator.

Since I am teaching Statistics, I want to do some calculation of the normal distribution probability.

Before I begin, I need to mention, in order to calculate the normal distribution probability something like P(x < X), this can be done by using a spreadsheet software with NORMDIST() and NORM.INV() for the inverse of the former function.

Spreadsheet is good for calculation, but not good as a calculator. My primary calculator is SpeedCrunch, which allows entering expression. But the drawback of SpeedCrunch is the lack of statistical functions.

Therefore, the functional programming comes to my mind.

Firstly, let me introduce the usage of Python. Make sure SciPy is installed. Run the Python interpreter,

from scipy.stats import norm
norm.cdf(my_value)
norm.ppf(my_probability)

So, the two functions are norm.cdf() (cumulative distribution function) and norm.ppf() (percent point function).

Now, let me introduce the usage of R language.

pnorm(my_value)
qnorm(my_probability)

R language is used for statistics, thus, no further module or library is required.

Both Python and R languages are not pure functional programmings. I wanted to try Emacs Lisp, but the arithmetic syntax is not convenient. The syntax is using Polish notation. In order to perform arithmetic calculation,

(* 2 (+ 3 6))

Therefore, I tried the pure functional programming language, that is, Haskell.

In order to calculate the normal distribution probability, the Statistics module is required. After installation,

import Statistics.Distribution
import Statistics.Distribution.Normal
let d = normalDistr 0 1
cumulative d 0
quantile d 0.5

“normalDistr 0 1” is to create a normal distribution with mean 0 and standard deviation 1. Then “cumulative d 0” is the calculation of CDF (cumulative distribution function), which produces 0.5. And “quantile” is the inverse function of CDF.

So, enjoy the functional programming in mathematics and statistics.

Xfce4 Power Manager, NVIDIA, Nouveau backlight issue

Recently I move back to use my (around) 4 years old laptop, HP Pavilion dv3. It has NVIDIA graphic card. But since I (re-)installed Arch Linux 64 bit on it, I failed to run the X11 with the proprietary NVIDIA driver. As a result, I used the Nouveau module instead. Then, I tried several times and finally successfully run the X11 with NVIDIA driver.

To use the Nouveau module, in the mkinitcpio.conf, we have to add in “nouveau” module, then build the initramfs (refer to wiki page). And use the “Xorg -configure” to generate the xorg.conf.

But in order to use the NVIDIA driver, firstly, has to identify the NVIDIA graphic card and download the related drivers. Secondly, since I am using 64 bit, but also running 32 bit packages, so I have to install all the corresponding lib32 NVIDIA packages. Moreover, the nvidia*-libgl are conflicted to mesa-libgl, which is used by Nouveau. After installing NVIDIA, use “nvidia-xconfig” to generate the xorg.conf.

We can also disable the splash screen (logo) when starting the X11, by adding

Options "NoLogo" "1"

in the “Device” section in the xorg.conf.

Then after using the NVIDIA, I face a serious problem, that is the xrandr (in fact I am usign ARandR) cannot change the screen resolution. This is troublesome as I need to make the changes towards the projector (2nd screen) frequently, such as two screens (left screen and right screen), laptop only (disable the projector), or clone (both laptop and the projector share the same screen). With the NVIDIA, xrandr cannot detect other resolutions, consequently I cannot make clone of the screen. So, I decided to use back Nouveau.

However, I have another serious problem with Nouveau module, that is, adjusting the backlight brightness (screen brightness). When I use xbacklight, it shows

No outputs have backlight property

I cannot adjust the backlight brightness using the usual keyboard key with Xfce4 Power Manager. Some forums stated that adding “acpi_backlight=xxxx” to the kernel parameter. But none of them works.

In my /sys/class/backlight, there are acpi_video0 and nv_backlight. Actually, I can change the backlight by echo the value to the acpi_video0/brightness, with “su”. Yet the nv_backlight does not show any effect.

I found that, I can use the keyboard key to adjust the brightness before start the Xfce4. Once the Xfce4 started (with Power Manager), the brightness change takes no effect. And the changes of the brightness is affecting the nv_backlight/brightness. So, I concluded that it is actually fixable by fixing the Xfce4 Power Manager.

As a result, I patched the Xfce4 Power Manager by editing the source code, to remove the “nv_backlight” from the priority. Install this patched package, restart the Xfce4, and now, it works!