initial commit

tomo/utils/tukeywin.m

@@ -0,0 +1,56 @@
+function w = tukeywin(n,r)
+%TUKEYWIN Tukey window.
+%   TUKEYWIN(N) returns an N-point Tukey window in a column vector.
+% 
+%   W = TUKEYWIN(N,R) returns an N-point Tukey window in a column vector. A
+%   Tukey window is also known as the cosine-tapered window.  The R
+%   parameter specifies the ratio of the length of taper section to the
+%   total length of the window. For a Tukey window, R is normalized to 1
+%   (i.e., 0 < R < 1). If omitted, R is set to 0.500.
+%   
+%   If R is outside the region of (0, 1), the Tukey window degenerates into
+%   other common windows. Thus when R = 1, it is equivalent to a Hanning
+%   window. Conversely, for R = 0 the Tukey window is equivalent to a
+%   boxcar window.
+%
+%   EXAMPLE:
+%      N = 64; 
+%      w = tukeywin(N,0.5); 
+%      plot(w); title('64-point Tukey window, Ratio = 0.5');
+%
+%   See also CHEBWIN, GAUSSWIN, KAISER, WINDOW.
+
+%   Reference:
+%     [1] fredric j. harris [sic], On the Use of Windows for Harmonic Analysis
+%         with the Discrete Fourier Transform, Proceedings of the IEEE,
+%         Vol. 66, No. 1, January 1978, Page 67, Equation 38.
+
+%   Author(s): A. Dowd
+%   Copyright 1988-2005 The MathWorks, Inc.
+
+narginchk(1,2);
+
+% Default value for R parameter.
+if nargin < 2 || isempty(r)
+    r = 0.500;
+end
+
+[n,w,trivialwin] = check_order(n);
+if trivialwin, return, end
+
+if r <= 0
+    w = ones(n,1);
+elseif r >= 1
+    w = hann(n);
+else
+    t = linspace(0,1,n)';
+    % Defines period of the taper as 1/2 period of a sine wave.
+    per = r/2; 
+    tl = floor(per*(n-1))+1;
+    th = n-tl+1;
+    % Window is defined in three sections: taper, constant, taper
+    w = [ ((1+cos(pi/per*(t(1:tl) - per)))/2);  ones(th-tl-1,1); ((1+cos(pi/per*(t(th:end) - 1 + per)))/2)];
+end
+
+
+% [EOF]