In general, wavelet packet crystals can be arranged in the so-called natural order
ala $W(0,0) , W(1,0), W(1,1), W(2,0), W(2,1), W(2,2), W(2,3), ... , W(J,0), ..., W(J, NJ)$
where $J$ is the number of decomposition levels and $NJ$.
By definition, $W(0,0)$ is the original time series.
A given crystal is identified in the $W(j,n)$ form above or by a flattened index.
For example, the DWPT crystal in level 2 at oscillation index 1 is identified either by j,n=2,1 or
by its flattened index 4 (with zero based indexing, 4 represents the fifth crystal of the wavelet packet
transform in natural order). This function converts such flattened wavelet packet indices to
the $W(j,n)$ form.