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Converting From A Normalized To Continuous Lowpass Filter
Syntax fn2clp(cutoffnumindeninnumoutdenout)
See Also fnbut , fncheb , fn2dlp

Description
Converts a normalized filter to a continuous lowpass filter. The real or double-precision scalar cutoff specifies the cutoff frequency for the lowpass filter. The column vector numin has the same type as cutoff and specifies the numerator polynomial for the normalized filter. The column vector denin has the same type as cutoff and specifies the denominator polynomial for the normalized filter.

The input values of numout and denout have no effect. The output value of numout is set to the column vector representing the numerator polynomial for the continuous lowpass filter. The output value of denout is set to the column vector representing the denominator polynomial for the continuous lowpass filter. The output values of numout and denout have the same type as cutoff.

The response of a continuous filter is
             2
     |num[s]|
     |------|
     |den[s]|

where num[s] is the numerator polynomial and den[s] is the denominator polynomial corresponding to the filter. The response of a normalized filter is near 1 for s in the interval
           __
     [0, \/-1]

and near 0 for the rest of the positive imaginary axis. The response of the continuous lowpass filter is near 1 for s in the interval
           __
     [0, \/-1 cutoff]

and near 0 for the rest of the positive imaginary axis.

Example
     numin = 1.
     denin = {1., sqrt(2.), 1.}
     numout = novalue
     denout = novalue
     cutoff = 2.
     fn2clp(cutoff, numin, denin, numout, denout)
     
     xmin = 1e-1
     xmax = 1e+1
     ymin = 1e-4
     ymax = 1e+2
     fcplot(xmin, xmax, ymin, ymax, cutoff, numout, denout)
     
returns the following plot: