Digital filter.

  Y = FILTER(B, A, X) filters the data in vector X with the

  filter described by vectors A and B to create the filtered

  data Y.  The filter is a "Direct Form II Transposed"

  implementation of the standard difference equation:



  y(n) = b(1)*x(n) + b(2)*x(n-1) + ... + b(nb+1)*x(n-nb)

                   - a(2)*y(n-1) - ... - a(na+1)*y(n-na)



  [Y,Zf] = FILTER(B,A,X,Zi) gives access to initial and final

  conditions, Zi and Zf, of the delays.



  See also FILTFILT in the Signal Processing Toolbox.