This function returns the vector H1, the quadrature mirror filter 
  of H0. If  H0 = [h0 h1 h2 ... h(M-1)] then your Z transform is:
  M2=floor(M/2);
  $H[Z] = h0 Z^{+M2} + h1 Z^{+M2-1} + ...  h(M-1) Z^{+M2-(M-1)}$ 
  and
  $H1[Z]=H0[-Z]$

  Additionally, the function returns $|D[Z=e^{i*W}]|$, where $D[Z] = H0^2[Z]-H0^2[-Z]$
  for W from 0 to pi.
 

  After starting the main routine just type the following command at the
  prompt:
  H1=qmfmirror(H0);
  [H1 AD]=qmfmirror(H0);
  [H1 AD]=qmfmirror(H0,N);
  [H1 AD FREQN]=qmfmirror(H0);
  [H1 AD FREQN]=qmfmirror(H0,N);
  
  Input:
  H0     is a vector with the parameters of a FIR filter.
  N      [Optional] is the number of analyzed points in AD.
  Output:
  H1     is the quadrature mirror filter of H0. H0[Z]=H1[-Z]
  AD     [Optional] is a modulus of $D[Z=e^{i*W}]$, where $D[Z] = H0^2[Z]-H0^2[-Z]$.
         The number of analyzed points in AD is equal to N.
  FREQN  [Optional] is the normalized frequency of points in AD, thus for the 
         point AD(id) we have W=FREQN(id)*pi.
  

  For help, bug reports and feature suggestions, please visit:
  http://nongnu.org/bsltl/

Package: bsltl