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Poles Of A Normalized Butterworth Filter
Syntax fnbpole(n)
See Also fnbut , fncpole , zero2pol

Returns the poles of a normalized Butterworth filter with n poles, where n is an integer scalar. Note that the poles come in conjugate pairs, so the corresponding polynomial is real. The return value is a complex column vector of length n with each element corresponding to a pole.

The following program computes the poles corresponding to a 7 pole Butterworth filter. It then converts the complex pole locations to polar coordinates (rtheta) and plots them.

p      = fnbpole(7)
r      = abs(p)
theta  = atan2(imag(p), double(p))
theta  = 180 * theta / PI
rmax   = 2.
rmajor = 2
tmajor = 4
style = "cross"
color = "black"
polar(r, theta, rmax, rmajor, tmajor, style, color)