ELI5: Explain Like I'm 5

Convergence of Fourier series

Okay, kiddo, have you ever heard of a melody or tune? Imagine you have a friend who loves music and asks you to play a song on your toy piano. You can play a few notes, but not the whole song. Your friend tells you to keep playing the same notes over and over again in a loop. This is called a periodic function, like when you take two steps forward and then two steps back, then repeat the same two steps again and again.

Now, let's use some magic to see the different ways to represent this periodic function. We will write down a series of numbers using a special method called Fourier series. This series tells us how much of each frequency of sound (high or low pitch) is needed to create the same periodic function. Just like when you add primary colors to make orange, green or purple.

But wait, there's more! Sometimes, the Fourier series we wrote down might not be the same as the original periodic function. That's because we didn't write down an infinite number of terms or numbers. We only wrote down a few. In math terms, this means that the Fourier series might not converge to the original function.

So, let's recap. Fourier series are a magical way to represent periodic functions using a series of numbers. However, sometimes we need an infinite number of numbers to make it match perfectly. Otherwise, it won't converge to the original function.

Did you understand, kiddo?