Orion has kindly created several tutorials (and is in the process of creating more) to shed light on Latent Semantic Indexing (LSI), as well as Singular Value Decomposition (SVD). LSI has been discussed in SEO forums for a few years, but I'm not sure anyone has ever really understood it. (I never even heard of SVD until tonight - sounds like a disease to me. Anyway, reading Orion's tutorials lets me know for sure that I have never understood LSI - and I possibly never will).
Although Orion begins his tutorial by explaining that these things are not too difficult to grasp, and they may not be for you math wizards out there, I quickly got lost. Still, even if you don't understand all the mathematics that are presented, here's the part you will understand. Orion lists in plain, simple English what LSI IS NOT! And that's worth its weight in gold right there. You can quickly get all of the myths and misconceptions out of your head.
So, here are the links you'll need:
Here's what I've learned from these tutorials. I will never ever think about LSI again. It would be pointless, since I will never understand it. 🙂