function [DH,DW] = multiband(N, F, GF, W, mags, delay)
%MULTIBAND Desired frequency response for multiband filters.
%  CREMEZ(N,F,{'multiband', M} ...) designs a linear-phase multiband
%  filter response using CREMEZ, where M is a vector of magnitudes,
%  one per band edge given in F.
%
%  CREMEZ(N,F,{'multiband', M, D}, ...) specifies group-delay offset D
%  such that the filter response will have a group delay of N/2 + D in
%  units of the sample interval, where N is the filter order.
%  Negative values create less delay, while positive values create
%  more delay.  By default, D=0.
%
%  The symmetry option SYM defaults to 'even' if unspecified in the
%  call to CREMEZ, if no negative band edge frequencies are
%  specified in F.
%
%  EXAMPLE: Design a 31-tap, complex lowpass filter
%    b = cremez(30,[-1 -.5 -.4 .7 .8 1],{'multiband',[0 0 1 2 0 0]});
%    freqz(b,1,512,'whole');
%
%  EXAMPLE: Reduced group delay filter response:
%    b = cremez(30,[-1 -.5 -.4 .7 .8 1],{'multiband',[0 0 1 2 0 0],-1});

%  See also CREMEZ.

%   Authors: L. Karam, J. McClellan
%   Revised: October 1996, D. Orofino
%
%   Copyright (c) 1988-98 by The MathWorks, Inc.
%   $Revision: 1.6 $  $Date: 1997/11/26 20:14:24 $

%  [DH,DW]=MULTIBAND(N,F,GF,W,MAGS,DELAY)
%       N: filter order (length minus one)
%       F: vector of band edges
%      GF: vector of frequencies at which to evaluate
%       W: vector of weights, one per band
%    MAGS: vector of mags, one per band edge
%   DELAY: negative slope of the phase.
%           N/2=(L-1)/2 for exact linear phase.
%
%     DH: vector of desired filter response (mag & phase)
%     DW: vector of weights (positive)
%
% NOTE: DH(GF) and DW(GF) are specified as functions of frequency

% Ex. 1: Assymetric complex response:
%   b=cremez(32,[-.8 -.5 -.3 .2 .4 .6],[1 1 0 0 1 1]);
%

% Support query by CREMEZ for the default symmetry option:
if nargin==2,
  % Return symmetry default:
  if strcmp(N,'defaults'),
    % Second arg (F) is cell-array of args passed later to function:
    num_args = length(F);
    % Get the delay value:
    if num_args<6, delay=0; else delay=F{6}; end
    % Use delay arg to base symmetry decision:
    if isequal(delay,0), DH='even'; else DH='real'; end
    return
  end
end

% Standard call:
error(nargchk(4,6,nargin));
if nargin<5,
  error(['Multiband designs requires specification of a ' ...
        'magnitude vector']);
end
if nargin<6, delay = 0; end
delay = delay + N/2;  % adjust for linear phase

W  = [1;1] * (W(:).');
DH = table1([F(:), mags(:)], GF) .* exp(-1i*pi*GF*delay);
DW = table1([F(:),    W(:)], GF);

% end of multiband.m