Author: Guy

Separate Numbering for Problems in LaTeX

By default when using the amsthm to create environments such as theorems, claims and problems, they all use the same numbering. Sometimes it’s annoying, as the numbering for the problems should generally be unaffected by the theorems present (or lack of them). For example the default behavior produces:

Problem 1
Problem 2
Theorem 3
Problem 4

where the desired behavior would be (in my opinion):

Problem 1
Problem 2
Theorem 1
Problem 3

Fortunately, this can be done by redefining the problem environment.

\let\problem\@undefined % undefines the existing problem environment
\theoremstyle{definition} % set the style of the new environment to 'definition'
\newtheorem{problem}{\protect\problemname} % (re)define the 'problem' environment

The \theoremstyle can be one of three defaults plain, definition and remark or some custom style defined using \newtheoremstyle.

See amsthm‘s documentation for more information, such as subordinately numbering (numbering per section).

Annoying Outlook Error

Sadly, there are occasions where I can’t use my beloved Gmail account and have to use Outlook to connected to a corporate Exchange servers. Due to Exchange inability to efficiently operate with large mailboxes (at least that what the tech support there tells me), I have to resort to so move messages to a local PST. However, some time a go I’ve started encountering the following error whenever I’ve tried moving messages into a PST file:

Cannot move the items. The item cannot be move. It was either already moved or deleted, or access was denied.

I’ve tried changing permissions, moving my PST around, repairing it with some tools that comes bundled with Office (I read somewhere that such error can be caused by corrupted PST files), and even tried creating a new PST. But, alas, the not so helpful message just wouldn’t get a way.
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Scanning Lecture Notes – Separating Colors

Continuing my journey to prefect my scanned lecture notes, I’ll be reviewing my efforts for finding a good way to threshold scanned notes to black and white. I’ve spent several days experimenting with this stuff, and I think I’ve managed to improve on the basic methods used.

In the process of experimenting, I’ve come up with what I think are the 3 main hurdles into scanning notes (or text in general) to black and white.

  1. Bleeding. When using both sides of the paper the ink might be “bleed” through to the other side. Even if the ink doesn’t actually pass through, it might still be visible as kind of shadow, when scanning, just like when you hold a piece of paper in front of a light and you’re able to make out the text on the other side.
  2. Non-black ink. Photocopying blue ink, is notoriously messy. Scanning it to b&w, also imposes challenges.
  3. Skipping. This is an artifact that sometimes introduced when writing with a ballpoint pen. It’s a result of inconsistent ink flow, and is more rare with more liquid inks such as rollerballs or fountain pens.

Those issue can be visualized in the first three images. These images are the originals I’ve tested the various methods with. The other images are results of the various methods, explained in this post, and should convey the difference between them.
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Scanning Lecture Notes – Compression

A new semester is about to begin, hence I again set out to organize lecture notes and scan them. This time I intend to invest more time investigating and perfecting this process. Hopefully, I’ll present my conclusions in few posts, each focusing on a different aspect.

In the first post, I’ll discuss the various ways to compress the scanned lecture notes. Because lecture notes (at least mine) aren’t especially colorful has I only use one pen at the time, I want the result to be black and white (line art). This allows readable lecture notes in while preserving small size per page (as you can see in Some Tips on Scanning Lecture Notes).
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Hebrew Support in Hyperref – Situation Review

It’s been a bit more than three years since I’ve written about a workaround for getting hyperref to play (almost) nicely with Hebrew. Over the past few weeks, I saw I rising interest in this and few people contacted me regarding this issue. So I thought it’s a good opportunity to better document the current situation, and possible ways that should be further investigated which I believe might lead to better solutions.
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Sending Desktop Notification from Cron

Usually when one wants to keep track of one’s cron jobs, one tells the cron daemon to email the output of the commands. While this is probably the best solution for servers, on desktop machines is problematic. Many ISPs block outgoing traffic on port 25 (SMTP), and if you want to send the emails via external SMTP server (such as GMail) this requires you to store authentication details in plain text. A better solution for the desktop would be to harness the desktop notifications available in Ubuntu.

There is a useful tool called notify-send which is able to send desktop notifications directly from the command line. However, there are few caveats:

  • notify-send expects its input on the command line, it can’t read from stdin.
  • If you run from cron you must tell it which display to use.

The first issue can be worked around by using cat to pick up the input. The second issue is handled by adding a DISPLAY environment variable to the crontab. So your crontab will look something like this:

DISPLAY=:0
10 1 * * sun some_cool_command | notify-send "Backup Documents" "$(cat)"

The first argument to notify-send is the title of the notification. The second is the actual text to appear in it, in our case it’s whatever comes in the stdin. If you want to store the output in a log file as well as displaying it in a desktop notification, you can use tee, which basically saves its input to a given file and also pipes it again to stdout.

DISPLAY=:0
10 1 * * sun some_cool_command | tee -a ~/some_log.log | notify-send "Backup Documents" "$(cat)"

WiFi won’t connect on Samsung Galaxy S2 with CyanogenMod 9 (ICS 4.0.4)

After upgrading to CyanogenMod 9 (ICS 4.0.4) I’ve experience problems connecting to WiFi networks. Most of the time I’ve tried to connect to a WiFi network it would try to connect and then fail. Often it would also show the network I’ve just tried to connect to as “Not in range”. This was extremely irritating, as I could stand by my router and have the phone report that there is no signal, while another Galaxy S2 phone would connect immediately, the only difference was that the other phone was running Android 2.3.7. Needless to say, I haven’t made any major (or minor) changes to my WiFi equipment and the problem wasn’t confined just to my home. Sometimes, it would connect after being idle for a day or so.

Back when I was using CyanogenMod 7, I had no problems with the WiFi on my phone, and I could also replicate this behaviour on another Galaxy S2 I’ve upgraded to CyanogenMod 9. Initially I thought it was some bug in CyanogenMod, but I came up with nothing. Over the weekend, I’ve figured maybe the bug isn’t specific to CyanogenMod, and I’ve found this bug report WiFi freeze on Samsung Galaxy S2 with ICS 4.0.3. For some reason many people have problems with WiFi on Galaxy S2 with ICS. While the report relates to the WiFi freezing, which I didn’t experience, I’ve decided to sift through the comments. Some people mentioned the “Wi-Fi frequency band” feature available in Wi-Fi settings -> Advanced (available by pressing the menu button), so I’ve decided to try playing with the different settings there.

This setting allows you to choose the WiFi operating frequency between three options 5GHz, 2.4GHz and “Auto”, which as you can guess automatically figures out the right frequency, 5GHz (802.11a and 802.11n) and 2.4GHz(802.11b/g/n). However, it seems the phone (probably due to a problem in the driver) fails the “Auto” thing. Instead of guessing the right frequency, it fails to connect. So I’ve changed it to 2.4GHz, which is still more popular choice in routers over 5GHz, and instantly my phone connected to my router.

For conclusion: If you have trouble connecting to WiFi on Samsung Galaxy S2 with ICS, you should probably set the phone to use 2GHz only (or 5GHz only) instead of the default “Auto” mode.

spass-3.0 Released

I’ve released today the new version of spass, a tool that creates cryptographically strong passwords and passphrases by generating random bits from your sound card.

In the user facing side, spass can now create passphrases as long as passwords. The words for the passphrases are chosen out of a list of 8192 words which means each word adds 13 bits of entropy to the passphrase.

spass can now use one of three audio backends (the old version could only use OSS):

  • Advanced Linux Sound Architecture (ALSA)
  • Open Sound System (OSS)
  • PortAudio

The PortAudio support will hopefully make it easy to port spass to other platforms as well (such as Windows). The random number generator got overhauled and now there is an unbiasing step before applying the hash function. This should help getting consistent results in terms of entropy. In the backstage I’ve migrated the project from autotools to cmake.

You can find more information, as well as both source and binary packages in https://github.com/guyru/spass.

Auto-Detect Dependencies when Building .debs Using CMake

CMake (via CPack) as a great feature that allows you to automatically generate Debian/Ubuntu (.deb) packages. One of the annoying things to do when you create a package is listing its dependencies. CMake asks you do it via the CPACK_DEBIAN_PACKAGE_DEPENDS variable. For example:

set (CPACK_DEBIAN_PACKAGE_DEPENDS "libc6 (>=2.7-18)")

But what happens when you work on a more complex project? Keeping track of all the dependencies by hand is a tedious task. Debian provides a tool named dpkg-shlibdeps which makes this task easier by updating the debian/control file with dependencies extracted from the dynamic libraries needed by a given executable. Luckily since CMake 2.8.3, CMake also supports running this tool automatically to figure out the required dependencies. The documentation is sparse, and I had hard time finding how to do so (I actually found it via a bug report and a commit message, but afterwards I’ve seen it the official documentation too). To enable it, you need to add the following line to your CMakeLists.txt file:

# autogenerate dependency information
set (CPACK_DEBIAN_PACKAGE_SHLIBDEPS ON)