Note:
The use of 
sigwin.flattopwin
creates a handle to a flat
top window object for use in spectral analysis and FIR filtering by
the window method. Object methods enable workspace import and ASCII
file export of the window values.
H = sigwin.flattopwin
returns a flat top
window object H
of length 64 with symmetric sampling.
H = sigwin.flattopwin(
returns a flat top window object of length Length
)Length
with symmetric sampling. Length
must be a positive integer. Entering a positive noninteger value
for Length
rounds the length to the nearest
integer. Entering a 1 for Length
results
in a window with a single value of 1.
H = sigwin.flattopwin(
returns a flat
top window object Length
,SamplingFlag
)H
of length Length
with sampling SamplingFlag
. The SamplingFlag
can be either 'symmetric'
or 'periodic'
.

Flat top window length. Must be a positive integer. Entering
a positive noninteger value for 


generate  Generates flat top window 
info  Display information about flat top window object 
winwrite  Save flat top window in ASCII file 
The following equation defines the flat top window of length N
:
$$w(n)={a}_{0}{a}_{1}\mathrm{cos}(2\pi n/(N1))+{a}_{2}\mathrm{cos}(4\pi n/(N1)){a}_{3}\mathrm{cos}(6\pi n/(N1))+{a}_{4}\mathrm{cos}(8\pi n/(N1)),\text{\hspace{1em}}0\le n\le M1$$
where M
is N/2
for N
even and (N+1)/2
for N
odd.
The second half of the symmetric flat top window $$M\le n\le N1$$ is obtained by flipping the first half around the midpoint. The symmetric option is the preferred method when using a flat top window in FIR filter design by the window method.
The periodic flat top window is constructed by extending the desired window length by one sample, constructing a symmetric window, and removing the last sample. The periodic version is the preferred method when using a flat top window in spectral analysis because the discrete Fourier transform assumes periodic extension of the input vector.
The coefficients are listed in the following table:
Coefficient  Value 

a0  0.21557895 
a1  0.41663158 
a2  0.277263158 
a3  0.083578947 
a4  0.006947368 
Handle. To learn how copy semantics affect your use of the class, see Copying Objects in the MATLAB^{®} Programming Fundamentals documentation.
Default length N = 64
symmetric flat top
window:
H = sigwin.flattopwin; wvtool(H)
Generate length N = 128
periodic flat top
window, return values, and write ASCII file:
H = sigwin.flattopwin(128,'periodic'); % Return window with generate win = generate(H); % Write ascii file in current directory % with window values winwrite(H,'flattopwin_128')
Oppenheim, Alan V., and Ronald W. Schafer. DiscreteTime Signal Processing. Upper Saddle River, NJ: Prentice Hall, 1989.