Correlation isn't a property of a pair of mathematical functions or a pair of physical systems, it's a property of a pair of random variables.
"A and B are correlated" means "Observing A can change your probabilistic beliefs about B".
If you already know that A and B are both sine waves, then neither has any belief-updating power over the others, there's no randomness in the random variables.
(I know that's not 100% precise... someone else please improve.)
People want to tell everything instead of telling the best 15 words. They want to learn everything instead of the best 15 words. In this thread, instead post the best 15-words from a book you've read recently (or anything else). It has to stand on its own. It's not a summary, the whole value needs to be contained in those words.
I'll start in the comments below.
(Voted by the Schelling study group as the best exercise of the meeting.)