1-D approximation coefficients

The input vectors `C`

and `L`

contain all the
information about the signal decomposition.

Let `NMAX = length(L)-2`

; then ```
C = [A(NMAX) D(NMAX) ...
D(1)]
```

where `A`

and the `D`

are vectors.
If `N = NMAX`

, then a simple extraction is done; otherwise,
`appcoef`

computes iteratively the approximation coefficients
using the inverse wavelet transform.