function [b] = wmtsa_qmf(a, inverse)% wmtsa_qmf -- Calculate quadrature mirror filter (QMF).%%****f* wmtsa.dwt/wmtsa_qmf%% NAME%   wmtsa_qmf -- Calculate quadrature mirror filter (QMF).%% USAGE%   [b] = function_name(a, [inverse])%% INPUTS%   * a           -- filter coefficients (vector).%   * inverse     -- (optional) flag for calculating inverse QMF (Boolean).%                    Default: inverse = 0 (FALSE).%% OUTPUTS%    b            - QMF coefficients (vector).%% SIDE EFFECTS%%% DESCRIPTION%    wmtsa_qmf calculates the quadrature mirror filter (QMF) of%    for the specified filter coefficients.  If a is a vector,%    the QMF of the vector is calculated.  If a is a matrix or higher%    order array, the QMF is calculated along the first dimension.%%   The inverse flag, if set, calculates the inverse QMF.  inverse%   is a Boolean values specified as (1/0, y/n, T/F or true/false).%% EXAMPLE%    % h is the QMF of g.%    g = [0.7071067811865475 0.7071067811865475];%    h = wmtsa_qmf(g);%%    % g is the inverse QMF of h.%    h = [0.7071067811865475 -0.7071067811865475];%    g = wmtsa_qmf(h, 1);%% ALGORITHM%      g_l = (-1)^(l+1) * h_L-1-l%      h_l = (-1)^l * g_L-1-l%    See pages 75 of WMTSA for additional details.%% REFERENCES%   Percival, D. B. and A. T. Walden (2000) Wavelet Methods for%   Time Series Analysis. Cambridge: Cambridge University Press.%% SEE ALSO%   yn%% TOOLBOX%   wmtsa/dwt%% CATEGORY%   Filters:  Utilities%% AUTHOR%   Charlie Cornish%% CREATION DATE%   2005-02-02%% COPYRIGHT%   (c) 2005  Charles R. Cornish%% CREDITS%%% REVISION%   $Revision: 612 $%%***%   $Id: wmtsa_qmf.m 612 2005-10-28 21:42:24Z ccornish $usage_str = ['Usage:  [b] = ', mfilename, ...             '(a, [inverse])'];error(nargerr(mfilename, nargin, [1:2], nargout, [0:1], 1, usage_str, 'struct'));if (~exist('inverse', 'var') || isempty(inverse))  inverse = 0;endL = length(a);if (wmtsa_isvector(a))  b = flipvec(a);else  b = flipdim(a, 1)endif (yn(inverse))  first = 1;else  first = 2;endb(first:2:end) = -b(first:2:end);  return