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Normalized Butterworth Filter Polynomials
Syntax fnbut(nnumoutdenout)
See Also fncheb , fnbpole , fcplot

Description
Computes the numerator and denominator polynomials for a normalized Butterworth filter with n poles, where n is an integer greater than 0.

The input values of numout and denout have no effect. The output value of numout is set to the double-precision column vector corresponding to the numerator polynomial of the Butterworth filter (numout is equal to the scalar 1 because normalized Butterworth filters have no zeros). The output value of denout is set to the double-precision column vector corresponding to the denominator polynomial of the Butterworth filter. The filter's response function is

     |numout[s]|2
     |---------|
     |denout[s]|

and it is near 1 for s in the interval
           __
     [0, \/-1 ]
     
and near 0 for the rest of the positive imaginary axis.

Example
     numout   = novalue
     denout   = novalue
     n        = 3
     fnbut(n, numout, denout)

     xmin   = 1e-2
     xmax   = 1e+2
     ymin   = 1e-4
     ymax   = 1e+1
     cutoff = 1.
     fcplot(xmin, xmax, ymin, ymax, cutoff, numout, denout)

returns the following plot: