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Converting From A Normalized To Continuous Highpass Filter
 Syntax `fn2chp(`wc, b_in, a_in, b, a`)` Include: `include spt\fn2chp.oms` See Also fn2clp , fn2cbp , fn2cbs
``` Arguments:   usage: include function\fn2chp.oms      wc: Real or Double scalar, specifying the desired cutoff frequency in [radians/sec]          for the new highpass filter.    b_in: Column Vector, Input , specifying the numerator   polynomial for the normalized filter.    a_in: Column Vector, Input , specifying the denominator polynomial for the normalized filter.       b: Column Vector, Output, returning  the numerator   polynomial for the highpass filter.       a: Column Vector, Output, returning  the denominator polynomial for the highpass filter. ```
Description ``` ```This function takes the numerator and denominator polynomials of a lowpass normalized continuous transfer function (Hin = b_in/a_in), converting and frequency translates them to the desired radian cutoff frequency [rad/sec] "wc" (Hout = b/a) of a new highpass filter. Sources of normalized filter transfer functions can be obtained from functions such as fn2chp , fn2cbp , fn2cbs , or, any similar user defined function. ``` ```The input and output polynomials are ascending polynomials in s = jw expressed as a column vector of length n as: ```           b => b(1) + n(2) * s + .. + b(n) * s^(n-1); similarly for a. ``` The output polynomials b and a must be declared before the function is called, though their types do not matter. They can be declared as type "b = novalue", "a = novalue", for instance. ``` ```Example ``` # Design CHEBYSHEV Type 1 lowpass prototype filter, fc = 1 [radian/sec] Norder  = 5;                 # Filter Order Ap      = 1d0;               # Passband Ripple b_in    = novalue;           # Declare numerator   polynomial a_in    = novalue;           # Declare denominator polynomial fncheb1(Norder, Ap, b_in, a_in);   # Make prototype filter # Convert filter to a new highpass cutoff frequency b  = novalue;                 # Declare output numerator   polynomial a  = novalue;                 # Declare output denominator polynomial fc = 1000d0;                  # New lowpass cutoff frequency wc = 2d0*PI*fc;               # Equivalent radian frequency fn2chp(wc, b_in, a_in, b, a); # Convert the filter # Evaluate this filter around its cutoff. fmin    =  1d2; # Plotting Limits fmax    =  1d4; ymax    =  10d0; ymin    = -60d0; N       = 201; # Plotting information          n       = seq(N)'-1d0; f       = logspace(log10(fmin),log10(fmax),N)'; H       = gains(b,a,f); HdB     = db20(H); ``` A plot of the resulting filter appears as: ``` ```