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function [c,Ls,g]=dwilt(f,g,M,L)
%DWILT Discrete Wilson transform
% Usage: c=dwilt(f,g,M);
% c=dwilt(f,g,M,L);
% [c,Ls]=dwilt(...);
%
% Input parameters:
% f : Input data
% g : Window function.
% M : Number of bands.
% L : Length of transform to do.
% Output parameters:
% c : $2M \times N$ array of coefficients.
% Ls : Length of input signal.
%
% `dwilt(f,g,M)` computes a discrete Wilson transform with *M* bands and
% window *g*.
%
% The length of the transform will be the smallest possible that is
% larger than the signal. *f* will be zero-extended to the length of the
% transform. If *f* is a matrix, the transformation is applied to each column.
%
% The window *g* may be a vector of numerical values, a text string or a
% cell array. See the help of |wilwin|_ for more details.
%
% `dwilt(f,g,M,L)` computes the Wilson transform as above, but does a
% transform of length *L*. *f* will be cut or zero-extended to length *L*
% before the transform is done.
%
% `[c,Ls]=dwilt(f,g,M)` or `[c,Ls]=dwilt(f,g,M,L)` additionally return the
% length of the input signal *f*. This is handy for reconstruction::
%
% [c,Ls]=dwilt(f,g,M);
% fr=idwilt(c,gd,M,Ls);
%
% will reconstruct the signal *f* no matter what the length of *f* is, provided
% that *gd* is a dual Wilson window of *g*.
%
% `[c,Ls,g]=dwilt(...)` additionally outputs the window used in the
% transform. This is useful if the window was generated from a description
% in a string or cell array.
%
% A Wilson transform is also known as a maximally decimated, even-stacked
% cosine modulated filter bank.
%
% Use the function |wil2rect|_ to visualize the coefficients or to work
% with the coefficients in the TF-plane.
%
% Assume that the following code has been executed for a column vector *f*::
%
% c=dwilt(f,g,M); % Compute a Wilson transform of f.
% N=size(c,2)*2; % Number of translation coefficients.
%
% The following holds for $m=0,\ldots,M-1$ and $n=0,\ldots,N/2-1$:
%
% If $m=0$:
%
% .. L-1
% c(m+1,n+1) = sum f(l+1)*g(l-2*n*M+1)
% l=0
%
% .. math:: c\left(1,n+1\right) = \sum_{l=0}^{L-1}f(l+1)g\left(l-2nM+1\right)
%
%
% If $m$ is odd and less than $M$
%
% .. L-1
% c(m+1,n+1) = sum f(l+1)*sqrt(2)*sin(pi*m/M*l)*g(k-2*n*M+1)
% l=0
%
% L-1
% c(m+M+1,n+1) = sum f(l+1)*sqrt(2)*cos(pi*m/M*l)*g(k-(2*n+1)*M+1)
% l=0
%
% .. math:: c\left(m+1,n+1\right) & = & \sqrt{2}\sum_{l=0}^{L-1}f(l+1)\sin(\pi\frac{m}{M}l)g(l-2nM+1)\\
% c\left(m+M+1,n+1\right) & = &
% \sqrt{2}\sum_{l=0}^{L-1}f(l+1)\cos(\pi\frac{m}{M}l)g\left(l-\left(2n+1\right)M+1\right)
%
% If $m$ is even and less than $M$
%
% .. L-1
% c(m+1,n+1) = sum f(l+1)*sqrt(2)*cos(pi*m/M*l)*g(l-2*n*M+1)
% l=0
%
% L-1
% c(m+M+1,n+1) = sum f(l+1)*sqrt(2)*sin(pi*m/M*l)*g(l-(2*n+1)*M+1)
% l=0
%
% .. math:: c\left(m+1,n+1\right) & = & \sqrt{2}\sum_{l=0}^{L-1}f(l+1)\cos(\pi\frac{m}{M}l)g(l-2nM+1)\\
% c\left(m+M+1,n+1\right) & = &
% \sqrt{2}\sum_{l=0}^{L-1}f(l+1)\sin(\pi\frac{m}{M}l)g\left(l-\left(2n+1\right)M+1\right)
%
% if $m=M$ and $M$ is even:
%
% .. L-1
% c(m+1,n+1) = sum f(l+1)*(-1)^(l)*g(l-2*n*M+1)
% l=0
%
% .. math:: c\left(M+1,n+1\right) = \sum_{l=0}^{L-1}f(l+1)(-1)^{l}g(l-2nM+1)
%
% else if $m=M$ and $M$ is odd
%
% .. L-1
% c(m+1,n+1) = sum f(l+1)*(-1)^l*g(l-(2*n+1)*M+1)
% l=0
%
% .. math:: c\left(M+1,n+1\right) = \sum_{k=0}^{L-1}f(l+1)(-1)^{l}g\left(l-\left(2n+1\right)M+1\right)
%
% See also: idwilt, wilwin, wil2rect, dgt, wmdct, wilorth
%
% References: bofegrhl96-1 liva95 dajajo91
% AUTHOR : Peter L. S��ndergaard.
% TESTING: TEST_DWILT
% REFERENCE: REF_DWILT
error(nargchk(3,4,nargin));
if nargin<4
L=[];
end;
assert_squarelat(M,M,1,'DWILT',0);
if ~isempty(L)
if (prod(size(L))~=1 || ~isnumeric(L))
error('%s: L must be a scalar','DWILT');
end;
if rem(L,1)~=0
error('%s: L must be an integer','DWILT');
end;
end;
% Change f to correct shape.
[f,Ls,W,wasrow,remembershape]=comp_sigreshape_pre(f,'DWILT',0);
if isempty(L)
% Smallest length transform.
Lsmallest=2*M;
% Choose a transform length larger than the signal
L=ceil(Ls/Lsmallest)*Lsmallest;
else
if rem(L,2*M)~=0
error('%s: The length of the transform must be divisable by 2*M = %i',...
'DWILT',2*M);
end;
end;
[g,info]=wilwin(g,M,L,'DWILT');
f=postpad(f,L);
% If the signal is single precision, make the window single precision as
% well to avoid mismatches.
if isa(f,'single')
g=single(g);
end;
% Call the computational subroutines.
c=comp_dwilt(f,g,M,L);