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Normalized Butterworth Filter Polynomials
 Syntax `fnbut(`n`, `numout`, `denout`)` 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: ``` ```