function y = invdau4( x )
% INVDAU4 Inverse 4 tap Daubechies wavelet kernel

% First define the filter kernels
c0 = 0.4829629;
c1 = 0.8365163;
c2 = 0.2241439;
c3 = -0.1294095;

d_kernel_l = [ c2 c1 c0 c3 ];
d_kernel_h = [ c3 -c0 c1 -c2 ];

%  Now re-order the input
[ size_v, size_h ] = size( x );
half = size_h / 2;
z = [ 1:size_h ];
z( 1:2:size_h ) = x( 1:1:half );
z( 2:2:size_h ) = x( half+1:1:size_h );

for start = 1:2:size_h
	if start > 2
		a = z( start-2:start+1 );
	else
		residual = 3 - start;
		a( 1:residual ) = z( size_h-residual+1:size_h );
		a( residual+1:4 ) = z( 1:4-residual );
	end
	y( start ) = a * d_kernel_l';
	y( start + 1 ) = a * d_kernel_h';
end