Inverse Dyadic Wavelet Transform
s = IWT_ATrou(dwt,L)
an n times J-L+1 matrix
Coarsest Level of V_0; L << J
original 1-d signal; length(x) = 2^J = n
1. filters are obtained with MakeATrouFilter
2. usually, length(qmf) < 2^(L+1)
3. The transformed signal can be obtained by FWT_ATrou