Butterworth analog filter
[pols,gain]=zpbutt(n,omegac)
integer (filter order)
real (cut-off angular frequency in radians per second)
resulting poles of filter
resulting gain of filter
computes the poles of a Butterworth analog
filter of order n
and cutoff frequency omegac
transfer function H(s) is calculated by H(s)=gain/real(poly(pols,'s'))