flattopwin(n, [periodic|symmetric])

Return the window f(w):

f(w) = 1 - 1.93 cos(2 pi w) + 1.29 cos(4 pi w)
- 0.388 cos(6 pi w) + 0.0322cos(8 pi w)

where w = i/(n-1) for i=0:n-1 for a symmetric window, or
w = i/n for i=0:n-1 for a periodic window.  The default
is symmetric.  The returned window is normalized to a peak
of 1 at w = 0.5.

This window has low pass-band ripple, but high bandwidth.

According to [1]:

The main use for the Flat Top window is for calibration, due
to its negligible amplitude errors.

[1] Gade, S; Herlufsen, H; (1987) "Use of weighting functions in DFT/FFT
analysis (Part I)", Bruel & Kjaer Technical Review No.3.