Generates a 3 term Blackman Window.
GBLACKMAN(N, spacing, "sym")
N 
 
An integer, the number of points to generate.  
spacing 
 
A real, the spacing (delta x) between points.  
"sym" 
 
Optional. A string, the symmetry flag.

A series.
W1: gblackman(100, .01)
generates a 100point symmetric 3 term Blackman window using the following formula:
where n is the n^{th} point (1 <= n <= N) and N is 100, the number of points. The spacing between samples is set to 0.01.
W2: gblackman(100, 0.01, "periodic")
Creates a 100 point periodic Blackman window that conforms to the ISO 184311 standard.
where n is the n^{th} point (1 <= n <= N) and N is the number of points to generate. The spacing between samples is set to 0.01.
The "sym" flag controls the window symmetry as follows:
"Symmetric" sets the last point to be the same value as the first point. For an N point symmetric window, a N1 point periodic window is effectively created and the N^{th} point is set to the same value as the first point.
"Periodic" or "iso" creates a periodic window function useful in spectrum analysis applications. "Periodic" or "iso" conforms to the ISO 184311 standard for windowing functions.
The Hamming, Hanning, Flattop and Blackman windows are part of the family of cosine window functions. The ISO 184311 standard periodic form of these windowing functions are defined by:
where K is the number of window coefficients and N is the length of the window. The symmetric form of the window can be constructed by setting N to N1.
For the Blackman window:
Use the BLACKMAN function command to automatically create and multiply a Blackman window with a series. For example:
blackman(W1)
multiplies Window 1 with a Blackman window of the same length and spacing as the series in W1.
See GBLACKMANHARRIS to generate a 4 term BlackmanHarris window.
Blackman, BlackmanHarris, Flattop, Hamming, Hanning and Kaiser Windows are useful in creating FIR filters and in preprocessing series for FFT calculations.
GBLACKMAN can also be invoked as GBLCKMAN.