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## 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 in 0 : n-1 for a symmetric window, or) {
## w = i/n for ( i in 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.
## This program is public domain.
flattopwin <- function(n, sym = c('symmetric', 'periodic')) {
sym = match.arg(sym)
if (sym == "symmetric")
divisor = n - 1
else
divisor = n
x = 2*pi * 0:(n-1) / divisor
w = (1-1.93*cos(x)+1.29*cos(2*x)-0.388*cos(3*x)+0.0322*cos(4*x))/4.6402
w
}
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