I now vaguely recall something from high school about multiplying matrices, but this fascinating article puts it all in context with the NSA’s abilities.
I suppose I can believe General Clapper when he says they are not “listening to our phone calls.” They don’t need or want to - not now anyway. They have rather created huge matrices, and and they ARE spending lots of money storing that data. If they see an interesting connection, they then go back (how long - 1 year, 5 years, 10 years?) and pull up all that stored data.
I think I had matrix algebra in my junior year of high school. It was fun but I can’t remember there being any practical examples. (That came later in college to some extent but it was still pretty theoretical.)
This article does show how matrices can be really useful.
Yes, all they have to really have is the metadata to get a really good picture. I’m not to the point of turning my cell phone off when moving about but I am using services like Tor a lot more.