NAG Library Routine Document

C09CDF

1  Purpose

2  Specification

3  Description

4  References

5  Parameters

1:     $\mathrm{NWLINV}$ – INTEGERInput

On entry: the number of levels to be used in the inverse multi-level transform. The number of levels must be less than or equal to $n_{\mathrm{fwd}}$, which has the value of parameter NWL as used in the computation of the wavelet coefficients using C09CCF. The data will be reconstructed to level $\left(\mathbf{NWL}-\mathbf{NWLINV}\right)$, where level $0$ is the original input dataset provided to C09CCF.

Constraint: $1\le \mathbf{NWLINV}\le \mathbf{NWL}$, where NWL is the value used in a preceding call to C09CCF.

2:     $\mathrm{LENC}$ – INTEGERInput

On entry: the dimension of the array C as declared in the (sub)program from which C09CDF is called.

Constraint: $\mathbf{LENC}\ge n_c$, where $n_c$ is the total number of coefficients that correspond to a transform with NWLINV levels and is unchanged from the preceding call to C09CCF.

3:     $\mathrm{C}\left(\mathbf{LENC}\right)$ – REAL (KIND=nag_wp) arrayInput

On entry: the coefficients of a multi-level wavelet transform of the dataset.

Let $q\left(\mathit{i}\right)$ be the number of coefficients (of each type) at level $\mathit{i}$, for $\mathit{i}=n_{\mathrm{fwd}},n_{\mathrm{fwd}}-1,\dots ,1$. Then, setting $k_1=q\left(n_{\mathrm{fwd}}\right)$ and $k_{\mathit{j}+1}=k_{\mathit{j}}+q\left(n_{\mathrm{fwd}}-\mathit{j}+1\right)$, for $\mathit{j}=1,2,\dots ,n_{\mathrm{fwd}}$, the coefficients are stored in C as follows:

$\mathbf{C}\left(\mathit{i}\right)$, for $\mathit{i}=1,2,\dots ,k_1$

Contains the level $n_{\mathrm{fwd}}$ approximation coefficients, $a_{n_{\mathrm{fwd}}}$.

$\mathbf{C}\left(\mathit{i}\right)$, for $\mathit{i}=k_1+1,\dots ,k_2$

Contains the level $n_{\mathrm{fwd}}$ detail coefficients $d_{n_{\mathrm{fwd}}}$.

$\mathbf{C}\left(\mathit{i}\right)$, for $\mathit{i}=k_j+1,\dots ,k_{j+1}$

Contains the level $n_{\mathrm{fwd}}-\mathit{j}+1$ detail coefficients, for $\mathit{j}=2,3,\dots ,n_{\mathrm{fwd}}$.

The values $q\left(\mathit{i}\right)$, for $\mathit{i}=n_{\mathrm{fwd}},n_{\mathrm{fwd}}-1,\dots ,1$, are contained in DWTLEV which is produced as output by a preceding call to C09CCF. See C09CCF for details.

4:     $\mathrm{N}$ – INTEGERInput

On entry: $n$, the length of the data array, $y$, to be reconstructed. For a full reconstruction of NWL levels, where NWL is as supplied to C09CCF, this must be the same as parameter N used in the call to C09CCF. For a partial reconstruction of $\mathbf{NWLINV}<\mathbf{NWL}$, this must be equal to $\mathbf{DWTLEV}\left(\mathbf{NWLINV}+2\right)$, as returned from C09CCF.

5:     $\mathrm{Y}\left(\mathbf{N}\right)$ – REAL (KIND=nag_wp) arrayOutput

On exit: the dataset reconstructed from the multi-level wavelet transform coefficients and the transformation options supplied to the initialization routine C09AAF.

6:     $\mathrm{ICOMM}\left(100\right)$ – INTEGER arrayCommunication Array

On entry: contains details of the discrete wavelet transform and the problem dimension for the forward transform previously computed by C09CCF.

7:     $\mathrm{IFAIL}$ – INTEGERInput/Output

On entry: IFAIL must be set to $0$, $-1\text{ or }1$. If you are unfamiliar with this parameter you should refer to Section 3.3 in the Essential Introduction for details.

For environments where it might be inappropriate to halt program execution when an error is detected, the value $-1\text{ or }1$ is recommended. If the output of error messages is undesirable, then the value $1$ is recommended. Otherwise, if you are not familiar with this parameter, the recommended value is $0$. When the value $-\mathbf{1}\text{ or }\mathbf{1}$ is used it is essential to test the value of IFAIL on exit.

On exit: $\mathbf{IFAIL}=\mathbf{0}$ unless the routine detects an error or a warning has been flagged (see Section 6).

6  Error Indicators and Warnings

$\mathbf{IFAIL}=1$

On entry, $\mathbf{NWLINV}=〈\mathit{\text{value}}〉$.
Constraint: $\mathbf{NWLINV}\ge 1$.

On entry, NWLINV is larger than the number of levels computed by the preceding call to C09CCF: $\mathbf{NWLINV}=〈\mathit{\text{value}}〉$, expected $=〈\mathit{\text{value}}〉$.

$\mathbf{IFAIL}=2$

On entry, LENC is set too small: $\mathbf{LENC}=〈\mathit{\text{value}}〉$.
Constraint: $\mathbf{LENC}\ge 〈\mathit{\text{value}}〉$.

$\mathbf{IFAIL}=4$

On entry, N is inconsistent with the value passed to the initialization routine: $\mathbf{N}=〈\mathit{\text{value}}〉$, N should be $〈\mathit{\text{value}}〉$.

$\mathbf{IFAIL}=6$

Either the initialization routine has not been called first or array ICOMM has been corrupted.

Either the initialization routine was called with $\mathbf{WTRANS}=\text{'S'}$ or array ICOMM has been corrupted.

$\mathbf{IFAIL}=-99$

An unexpected error has been triggered by this routine. Please contact NAG.

See Section 3.8 in the Essential Introduction for further information.

$\mathbf{IFAIL}=-399$

Your licence key may have expired or may not have been installed correctly.

See Section 3.7 in the Essential Introduction for further information.

$\mathbf{IFAIL}=-999$

Dynamic memory allocation failed.

See Section 3.6 in the Essential Introduction for further information.

7  Accuracy

8  Parallelism and Performance

9  Further Comments

10  Example