## Copyright (C) 2002 John W. Eaton
##
## This file is part of Octave.
##
## Octave is free software; you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 2, or (at your option)
## any later version.
##
## Octave is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
## General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with Octave; see the file COPYING.  If not, write to the Free
## Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
## 02110-1301, USA.

## -*- texinfo -*-
## @deftypefn {Function File} {} freqz_plot (@var{w}, @var{h})
## Plot the pass band, stop band and phase response of @var{h}.
## @end deftypefn

## Author: Paul Kienzle <pkienzle@users.sf.net>

function freqz_plot (w, h)

    n = length (w);

    ## ## exclude zero-frequency
    ## h = h (2 : length (h));
    ## w = w (2 : length (w));
    ## n = n-1;

    mag = 20 * log10 (abs (h));
    phase = unwrap (arg (h));
    maxmag = max (mag);

    subplot (3, 1, 1);
    plot (w, mag);
    grid ("on");
    legend("Pass band (dB)");
    axis ([w(1), w(n), maxmag-3, maxmag], "labely");

    subplot (3, 1, 2);
    plot (w, mag);
    grid ("on");
    legend ("Stop band (dB)");
    if (maxmag - min (mag) > 100)
      axis ([w(1), w(n), maxmag-100, maxmag], "labely");
    else
      axis ("autoy", "labely");
    endif

    subplot (3, 1, 3);
    plot (w, phase*360/(2*pi));
    grid ("on");
    legend ("Phase (degrees)");
    xlabel ("Frequency");
    axis ([w(1), w(n)], "autoy", "label");

endfunction