# PDP 4

This week, I learned about deep learning and neural networks, and I wrote a handful of blog posts relating to concepts I learned last week.

The most poignant of these posts was Language: A Cluster Analysis of Reality. Taking inspiration from Eliezer Yudkowsky’s essay series A Human’s Guide To Words, and pieces of what I learned last week about cluster analyses, I created an abstract comparison between human language and cluster analyses done on n-dimensional reality-space.

Besides this, I started learning in depth about machine learning. I learned about the common loss functions, L2-norm and cross-entropy. I learned about the concept of deep neural nets: not just the theory, but the practice, all the way down to the math. I figured out what gradient descent is, and I’m getting started with TensorFlow. I’ll have more detail on all of this next week: there’s a lot I still don’t understand, and I don’t want to give a partially misinformed synopsis.

The most unfortunate part of this week was certainly that in order to fully understand deep neural networks, you need calculus, because a decent portion of the math relies on partial derivatives. I did statistics instead of calculus in high school, since I dramatically prefer probability theory to differential equations, so I don’t actually have all that much in the way of calculus, and there was an upper bound on how much of the math I actually got. I think that I’ll give myself a bit of remedial calculus in the next week.

The most fortunate part of this week was the discovery of how legitimately useful my favorite book is. Around four or five years ago, I read Rationality: From AI to Zombies. It’s written by a dude who’s big on AI, so obviously it contains rather a lot referencing that subject. When I first read it, I knew absolutely nothing about AI, so I just kind of skimmed over it, except to the extent that I was able to understand the fundamental theory by osmosis. However, I’ve been recently rereading Rationality for completely unrelated reasons, and the sections on AI are making a lot more sense to me now. The sections on AI are scattered through books 3, 4, and 5: The Machine in the Ghost, Mere Reality, and Mere Goodness.

And the most unexpected part of this week was that I had a pretty neat idea for a project, entirely unrelated to any of this other stuff I’ve been learning. I think I’ll program it in JavaScript over the next week, on top of this current project. It’s not complicated, so it shouldn’t get in the way of any of my higher-priority goals, but I had the idea because I would personally find it very useful. (Needless to say, I’ll be documenting that project on this blog, too.)