Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / signal-1.1.3 / flattopwin.m

diff --git a/octave_packages/signal-1.1.3/flattopwin.m b/octave_packages/signal-1.1.3/flattopwin.m
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+## Author: Paul Kienzle <pkienzle@users.sf.net> (2004)
+## This program is granted to the public domain.
+
+## flattopwin(L, [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/(L-1) for i=0:L-1 for a symmetric window, or
+## w = i/L for i=0:L-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.
+
+function w = flattopwin (L, sym)
+  if nargin == 0 || nargin > 2
+    print_usage;
+  endif
+
+  divisor = L-1;
+  if nargin > 1
+    match = strmatch(sym,['periodic';'symmetric']);
+    if isempty(match),
+      error("window type must be periodic or symmetric");
+    elseif match == 1
+      divisor = L;
+    else
+      divisor = L-1;
+    endif
+  endif
+    
+  x = 2*pi*[0:L-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;
+endfunction