## Talking Directly to a Web Server

If you want to talk directly to a web server, you can telnet to port 80 and type your HTTP requests on the console. (You can do this with other services too, if you telnet to the right port.) This might be useful if you’re trying to debug a connection. Here’s an example:

## Trace Tricks

The trace of a square matrix is the sum of the elements on the main diagonal. That is, for an n by n square matrix A, the trace of A is $$\mathrm{tr}(A) = \sum_{i=1}^n A_{ii} .$$ This might not seem too exciting at first. However, the trace operator has a neat quasi-commutative property: for matrices U and V, so long as the internal dimensions work out, it … [Read more…]

## Welcome

After a long hiatus, I’ve decided to get back into blogging. I’m closing my old blog and rebooting on this site. For now, this will be a tutorial-style blog. Posts will consist of quick tips, tricks, and lessons on subjects that I (and hopefully you) find useful.