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Normalized Chebychev Type 2 Lowpass Filter
 Syntax `fncheb2(`Norder, Ap, As, b, a`)` Include: `include spt\fncheb2.oms` See Also fnbut , fncheb1 , fnbes
``` ARGUMENTS:    INPUTS:       Norder = SCALAR. Requested order of transfer function. Coerced to                INTEGER before local processing. Norder >= 2.       Ap     = SCALAR. Passband attenuation in dB at cutoff frequency,                Ap > 0.0 dB. Coerced to DOUBLE for local processing.       As     = SCALAR. Stopband minimum attenuation in dB, As > Ap.                Coerced to DOUBLE for local processing.       b      = VECTOR, COLUMN, for return (type disregarded on input).                Numerator polynomial coefficients. Type DOUBLE.       a      = VECTOR, COLUMN, for return (type disregarded on input).                Denominator polynomial coefficients. Type DOUBLE.    RETURN: novalue. Filter functions are returned in 'b' and 'a'. ```
Description ``` ```This function creates a normalized TYPE 2 Chebychev s-domain lowpass transfer function of the form: H(s) = b(s)/a(s). The cutoff frequency is set to 1 radian/sec at an attenuation of 'Ap' dB, where Ap > 0.0 dB. The requested filter order 'Norder' must be >= 2. The numerator polynomial of the transfer function is returned through argument 'b', and is a column vector where the elements form a polynomial as follows: ``` ```b => b(1) + b(2)*s + b(3)*s^2 + ... ``` ```Denominator polynomial is returned in argument 'a', and is of the same form. ``` ```A Chebychev TYPE 2 filter (sometimes called the Inverse Chebychev Filter) has monotonic behavior in the passband and equi-ripple attenuation in the stopband of maximum value 'As' dB, where As > Ap.

Example ``` include spt\fncheb2.oms # Design CHEBYCHEV Type 2 lowpass prototype filter, fc = 1 [radian/sec] Norder = 5;        # Filter Order Ap     = 2d0;      # Passband variation As     = 45d0;     # Stopband attenuation b      = novalue;  # Declare numerator   polynomial a      = novalue;  # Declare denominator polynomial  fncheb2(Norder, Ap, As, b , a ); # Make the filter # Evaluate this filter around its cutoff. fmin    =  1d-2; # Plotting Limits fmax    =  1d1; ymax    =  10d0; ymin    = -60d0; N       = 301; # Plotting information n       = seq(N)'-1d0; f       = logspace(log10(fmin),log10(fmax),N)'; H       = gains(b,a,f); HdB     = db20(H); fc      = 1d0/2/PI; # Ap dB down at this cutoff ``` A plot of the normalized CHEBYSHEV Type 2 filter appears as: ``` ``` ``` ```Reference
Blinchikoff ``` ```