Fourier Series Tilda function


tilda function is non-[Periodic Function](https://texonom.com/periodic-function-3fa775a544934003bfbf39101551d1e1) 
when we sample, it become periodic
time 주기 신호에서 sampling하면 각각 계수가 되어 반대 도메인이 주기가 된다!



> [What does tilde on top of functions mean in fourier series and fourier transforms?](https://math.stackexchange.com/questions/3286976/what-does-tilde-on-top-of-functions-mean-in-fourier-series-and-fourier-transform)






