## Mathmatical expression

For scientific purpose, we sometime need to shift phase of time series with specfic angles.
To acheive this, we can transform the time series into freqeuency domain with
$$F(\omega) = \int_{-\omega}^{\omega} f(t) e^{-i \omega t} dt$$

where $F(\omega)$ as Fourier spectrum of signal $f(t)$. Thus, the phase shifted Fourier
spectrum $F_{sh}$ is

$$F_{sh}(\omega) = F(\omega) * e^{-i \alpha}$$