Flat top weighted window
w = flattopwin(L)
w = flattopwin(L,sflag)
Flat top windows have very low passband ripple (< 0.01 dB) and are used primarily for calibration purposes. Their bandwidth is approximately 2.5 times wider than a Hann window.
w = flattopwin(L,sflag) returns the L-point symmetric flat top window using sflag window sampling, where sflag is either 'symmetric' or 'periodic'. The 'periodic' flag is useful for DFT/FFT purposes, such as in spectral analysis. The DFT/FFT contains an implicit periodic extension and the periodic flag enables a signal windowed with a periodic window to have perfect periodic extension. When 'periodic' is specified, flattopwin computes a length L+1 window and returns the first L points. When using windows for filter design, the 'symmetric' flag should be used.
 D'Antona, Gabriele, and A. Ferrero. Digital Signal Processing for Measurement Systems. New York: Springer Media, 2006, pp. 70–72.
 Gade, Svend, and Henrik Herlufsen. "Use of Weighting Functions in DFT/FFT Analysis (Part I)." Windows to FFT Analysis (Part I): Brüel & Kjær Technical Review, No. 3, 1987, pp. 1–28.