I'm trying to do something very simple... I'd like to have a sine function, where the frequency is controlled by a separate frequency function Something like this: g(t) = sin(2*pi*f(t)*t) Assume that f(t) = 20*exp(-2*t)+4 I would expect a sine wave that starts at 24 Hz and then slowly slows down to 4 Hz. But when I plot it, I get some strange results for t in [0.5, 2], see attached image. The frequency for those values is very low. How's that possible? Is it my plotting program that acts funny? How can I get the expected (described) behaviour? Thanks in advance!