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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.

Change of Focus

I'll be heading Stateside soon to pursue my doctorate. Expect to see a big change of focus in this blog. I plan to use it to document some of my learning and to keep in touch with home.

Epic Fail

Courtesy FAILBLOG.

MacGyver Tip: Get Red Wine Out of Carpet

So I knocked a full bottle of red wine over in my kitchen today, and it smashed and flooded my carpet with red wine. Smooth, eh?

Fortunately, I was saved by the Internet: a solution of Dawn dishwashing soap and hydrogen peroxide took the stain out beautifully without wrecking the carpet's coloring. Chemistry is cool.

Link: http://www.stratsplace.com/patty_wine_stain.html