Scilab Function

analpf - create analog low-pass filter

### Calling Sequence

  `[hs,pols,zers,gain]=analpf(n,fdesign,rp,omega)`

### Parameters

- `n` : positive integer : filter order
- `fdesign` : string : filter design method : `'butt'` or `'cheb1'` or `'cheb2'` or `'ellip'`
- `rp` : 2-vector of error values for cheb1, cheb2 and ellip filters where only `rp(1)` is used for cheb1 case, only `rp(2)` is used for cheb2 case, and `rp(1)` and `rp(2)` are both used for ellip case. `0<rp(1),rp(2)<1`

- `-` for cheb1 filters `1-rp(1)<ripple<1` in passband
- `-` for cheb2 filters `0<ripple<rp(2)` in stopband
- `-` for ellip filters `1-rp(1)<ripple<1` in passband `0<ripple<rp(2)` in stopband

- `omega` : cut-off frequency of low-pass filter in Hertz
- `hs` : rational polynomial transfer function
- `pols` : poles of transfer function
- `zers` : zeros of transfer function
- `gain` : gain of transfer function

### Description

Creates analog low-pass filter with cut-off frequency at omega.

`hs=gain*poly(zers,'s')/poly(pols,'s')`

### Examples

    //Evaluate magnitude response of continuous-time system
    hs=analpf(4,'cheb1',[.1 0],5)
    fr=0:.1:15;
    hf=freq(hs(2),hs(3),%i*fr);
    hm=abs(hf);
    plot(fr,hm)

### Author

C. B.