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SciPy's eigh - How to Lose an Afternoon

So the SciPy package for Python is full of lots of goodness.  Be very careful using the eigh() routine to get eigenvalues, though.  There's a "gotcha" buried in it.

The syntax is:

(eigenvalues, eigenvectors) = eigh(matrix)

This returns an array of eigenvalues and a 2D array of eigenvectors (each eigenvector consists of many components).

And there's the gotcha.  Let's say you want the nth eigenvalue and eigenvector.  I would write:

eigenvalues[n]
eigenvectors[n]

And I would be horribly wrong.  The eigenvectors and eigenvalues do share an index, but the index on the eigenvector is SECOND column:

eigenvectors[:,n]

Seriously WTF.

Update: It turns out that this is due to eigh() being part of LAPACK, which is a non-Python library (Fortran?) that has a different internal storage model for 2D arrays.  So possibly less WTF, but still dangerous as all hell.

HOWTO: Tether a Blackberry 8300 Curve to a Macbook Pro on Rogers

This article contains details for Rogers.  Details for other providers can be found on Jeff Starr's excellent article.

1. Open up Jeff's article, linked above.
2. Follow all of the instructions for installing the modem script.
3. Follow all of the instructions for pairing the Blackberry to the Mac.
4. Follow the instructions for configuring the connection, BUT use these values for Rogers:
   Telephone Number = internet.com
   Username = wapuser1
   Password = wap
5. Click the modem icon in the menubar, and choose "Connect Bluetooth"
6. You're on the net!

Thanks to HowardForums for the Rogers settings.

Fixing Login->User Associations in SQL Server

This post is for me.  It's about something I am always forgetting.

In Microsoft SQL Server, a database server has logins and each database has users.  Every user is associated to one login.  If you detach a database from one server and move it to another (or, equivalently, backup and restore to a different machine) then your user is no longer associated to a valid login.  This happens even if you have a login on the new machine with the same name as on the old machine.

Effect?  No access.

It's easy to fix, though.  As sa, run this stored procedure in the affected database:

SP_CHANGE_USERS_LOGIN UPDATE_ONE, 'username', 'login_name'

My New Machine

This is my first post from a new machine.  It's a Dell Inspiron 9400 laptop, with the new Core Duo processor from Intel.  It also features the nVidia GeForce Go 7800 video card, which is really improving my Call of Duty game.

I had three main reasons for an upgrade (besides "I can"):

1. I hated my old 1024x768 15-inch display.  I have dual 19-inch 1600x1200 at work, and they have completely spoiled me.  I felt like I was looking through a porthole on a ship instead of the gigantic observation deck on a train.  This new one has a 1960x1200 display, which should address my concerns nicely.
2. I was getting frustrated by having a separate file system on my laptop as opposed to my desktop.  There were several times where I couldn't do what I needed to do while out and about because I had forgotten to copy something or what have you.
3. My old system couldn't play Call of Duty 2.  After five years of incredible service, it had finally been outclassed.

Despite the size of the system (it's 15.5 inches wide), it's actually lighter than my old notebook.  That, combined with the convenience of the dock, the integrated wireless and the spiffy carrying case will hopefully encourage some mobility.

In any case, it's a nice new toy!  Scott, Jay and Paul: I think it'll handle CoV nicely.

Speeding Up Windows XP

Willer found an excellent article on speeding up Windows XP.  Basically, turn off junk that's useless and stop pretending that your machine is under powered.

BUSY, busy, busy.  Personal update later.