# NAG FL Interfacec09fcf (dim3_​multi_​fwd)

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## 1Purpose

c09fcf computes the three-dimensional multi-level discrete wavelet transform (DWT). The initialization routine c09acf must be called first to set up the DWT options.

## 2Specification

Fortran Interface
 Subroutine c09fcf ( m, n, fr, a, lda, sda, lenc, c, nwl,
 Integer, Intent (In) :: m, n, fr, lda, sda, lenc, nwl Integer, Intent (Inout) :: icomm(260), ifail Integer, Intent (Out) :: dwtlvm(nwl), dwtlvn(nwl), dwtlvfr(nwl) Real (Kind=nag_wp), Intent (In) :: a(lda,sda,fr) Real (Kind=nag_wp), Intent (Inout) :: c(lenc)
#include <nag.h>
 void c09fcf_ (const Integer *m, const Integer *n, const Integer *fr, const double a[], const Integer *lda, const Integer *sda, const Integer *lenc, double c[], const Integer *nwl, Integer dwtlvm[], Integer dwtlvn[], Integer dwtlvfr[], Integer icomm[], Integer *ifail)
The routine may be called by the names c09fcf or nagf_wav_dim3_multi_fwd.

## 3Description

c09fcf computes the multi-level DWT of three-dimensional data. For a given wavelet and end extension method, c09fcf will compute a multi-level transform of a three-dimensional array $A$, using a specified number, ${n}_{\mathrm{fwd}}$, of levels. The number of levels specified, ${n}_{\mathrm{fwd}}$, must be no more than the value ${l}_{\mathrm{max}}$ returned in nwlmax by the initialization routine c09acf for the given problem. The transform is returned as a set of coefficients for the different levels (packed into a single array) and a representation of the multi-level structure.
The notation used here assigns level $0$ to the input data, $A$. Level 1 consists of the first set of coefficients computed: the seven sets of detail coefficients are stored at this level while the approximation coefficients are used as the input to a repeat of the wavelet transform at the next level. This process is continued until, at level ${n}_{\mathrm{fwd}}$, all eight types of coefficients are stored. All coefficients are packed into a single array.

## 4References

Wang Y, Che X and Ma S (2012) Nonlinear filtering based on 3D wavelet transform for MRI denoising URASIP Journal on Advances in Signal Processing 2012:40

## 5Arguments

1: $\mathbf{m}$Integer Input
On entry: the number of rows of each two-dimensional frame.
Constraint: this must be the same as the value m passed to the initialization routine c09acf.
2: $\mathbf{n}$Integer Input
On entry: the number of columns of each two-dimensional frame.
Constraint: this must be the same as the value n passed to the initialization routine c09acf.
3: $\mathbf{fr}$Integer Input
On entry: the number of two-dimensional frames.
Constraint: this must be the same as the value fr passed to the initialization routine c09acf.
4: $\mathbf{a}\left({\mathbf{lda}},{\mathbf{sda}},{\mathbf{fr}}\right)$Real (Kind=nag_wp) array Input
On entry: the $m×n×\mathit{fr}$ three-dimensional input data $A$, where with ${A}_{ijk}$ stored in ${\mathbf{a}}\left(i,j,k\right)$.
5: $\mathbf{lda}$Integer Input
On entry: the first dimension of the array a as declared in the (sub)program from which c09fcf is called.
Constraint: ${\mathbf{lda}}\ge {\mathbf{m}}$.
6: $\mathbf{sda}$Integer Input
On entry: the second dimension of the array a as declared in the (sub)program from which c09fcf is called.
Constraint: ${\mathbf{sda}}\ge {\mathbf{n}}$.
7: $\mathbf{lenc}$Integer Input
On entry: the dimension of the array c as declared in the (sub)program from which c09fcf is called.
Constraint: ${\mathbf{lenc}}\ge {n}_{\mathrm{ct}}$, where ${n}_{\mathrm{ct}}$ is the total number of wavelet coefficients that correspond to a transform with nwl levels.
8: $\mathbf{c}\left({\mathbf{lenc}}\right)$Real (Kind=nag_wp) array Output
On exit: the coefficients of the discrete wavelet transform. If you need to access or modify the approximation coefficients or any specific set of detail coefficients then the use of c09fyf or c09fzf is recommended. For completeness the following description provides details of precisely how the coefficients are stored in c but this information should only be required in rare cases.
Let $q\left(\mathit{i}\right)$ denote the number of coefficients of each type at level $\mathit{i}$, for $\mathit{i}=1,2,\dots ,{n}_{\mathrm{fwd}}$, such that $q\left(i\right)={\mathbf{dwtlvm}}\left({n}_{\mathrm{fwd}}-i+1\right)×{\mathbf{dwtlvn}}\left({n}_{\mathrm{fwd}}-i+1\right)×{\mathbf{dwtlvfr}}\left({n}_{\mathrm{fwd}}-i+1\right)$. Then, letting ${k}_{1}=q\left({n}_{\mathrm{fwd}}\right)$ and ${k}_{\mathit{j}+1}={k}_{\mathit{j}}+q\left({n}_{\mathrm{fwd}}-⌈\mathit{j}/7⌉+1\right)$, for $\mathit{j}=1,2,\dots ,7{n}_{\mathrm{fwd}}$, 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, ${a}_{{n}_{\mathrm{fwd}}}$. Note that for computational efficiency reasons these coefficients are stored as ${\mathbf{dwtlvm}}\left(1\right)×{\mathbf{dwtlvn}}\left(1\right)×{\mathbf{dwtlvfr}}\left(1\right)$ in c.
${\mathbf{c}}\left(\mathit{i}\right)$, for $\mathit{i}={k}_{j}+1,\dots ,{k}_{j+1}$
Contains the level ${n}_{\mathrm{fwd}}-⌈j/7⌉+1$ detail coefficients. These are:
• LLH coefficients if ;
• LHL coefficients if ;
• LHH coefficients if ;
• HLL coefficients if ;
• HLH coefficients if ;
• HHL coefficients if ;
• HHH coefficients if ,
for $j=1,\dots ,7{n}_{\mathrm{fwd}}$. See Section 2.1 in the C09 Chapter Introduction for a description of how these coefficients are produced.
Note that for computational efficiency reasons these coefficients are stored as ${\mathbf{dwtlvfr}}\left(⌈j/7⌉\right)×{\mathbf{dwtlvm}}\left(⌈j/7⌉\right)×{\mathbf{dwtlvn}}\left(⌈j/7⌉\right)$ in c.
9: $\mathbf{nwl}$Integer Input
On entry: the number of levels, ${n}_{\mathrm{fwd}}$, in the multi-level resolution to be performed.
Constraint: $1\le {\mathbf{nwl}}\le {l}_{\mathrm{max}}$, where ${l}_{\mathrm{max}}$ is the value returned in nwlmax (the maximum number of levels) by the call to the initialization routine c09acf.
10: $\mathbf{dwtlvm}\left({\mathbf{nwl}}\right)$Integer array Output
On exit: the number of coefficients in the first dimension for each coefficient type at each level. ${\mathbf{dwtlvm}}\left(\mathit{i}\right)$ contains the number of coefficients in the first dimension (for each coefficient type computed) at the (${n}_{\mathrm{fwd}}-\mathit{i}+1$)th level of resolution, for $\mathit{i}=1,2,\dots ,{n}_{\mathrm{fwd}}$.
11: $\mathbf{dwtlvn}\left({\mathbf{nwl}}\right)$Integer array Output
On exit: the number of coefficients in the second dimension for each coefficient type at each level. ${\mathbf{dwtlvn}}\left(\mathit{i}\right)$ contains the number of coefficients in the second dimension (for each coefficient type computed) at the (${n}_{\mathrm{fwd}}-\mathit{i}+1$)th level of resolution, for $\mathit{i}=1,2,\dots ,{n}_{\mathrm{fwd}}$.
12: $\mathbf{dwtlvfr}\left({\mathbf{nwl}}\right)$Integer array Output
On exit: the number of coefficients in the third dimension for each coefficient type at each level. ${\mathbf{dwtlvfr}}\left(\mathit{i}\right)$ contains the number of coefficients in the third dimension (for each coefficient type computed) at the (${n}_{\mathrm{fwd}}-\mathit{i}+1$)th level of resolution, for $\mathit{i}=1,2,\dots ,{n}_{\mathrm{fwd}}$.
13: $\mathbf{icomm}\left(260\right)$Integer array Communication Array
On entry: contains details of the discrete wavelet transform and the problem dimension as setup in the call to the initialization routine c09acf.
On exit: contains additional information on the computed transform.
14: $\mathbf{ifail}$Integer Input/Output
On entry: ifail must be set to $0$, $-1$ or $1$ to set behaviour on detection of an error; these values have no effect when no error is detected.
A value of $0$ causes the printing of an error message and program execution will be halted; otherwise program execution continues. A value of $-1$ means that an error message is printed while a value of $1$ means that it is not.
If halting is not appropriate, the value $-1$ or $1$ is recommended. If message printing is undesirable, then the value $1$ is recommended. Otherwise, the value $0$ is recommended. When the value $-\mathbf{1}$ 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).

## 6Error Indicators and Warnings

If on entry ${\mathbf{ifail}}=0$ or $-1$, explanatory error messages are output on the current error message unit (as defined by x04aaf).
Errors or warnings detected by the routine:
${\mathbf{ifail}}=1$
On entry, ${\mathbf{fr}}=⟨\mathit{\text{value}}⟩$.
Constraint: ${\mathbf{fr}}=⟨\mathit{\text{value}}⟩$, the value of fr on initialization (see c09acf).
On entry, ${\mathbf{m}}=⟨\mathit{\text{value}}⟩$.
Constraint: ${\mathbf{m}}=⟨\mathit{\text{value}}⟩$, the value of m on initialization (see c09acf).
On entry, ${\mathbf{n}}=⟨\mathit{\text{value}}⟩$.
Constraint: ${\mathbf{n}}=⟨\mathit{\text{value}}⟩$, the value of n on initialization (see c09acf).
${\mathbf{ifail}}=2$
On entry, ${\mathbf{lda}}=⟨\mathit{\text{value}}⟩$ and ${\mathbf{m}}=⟨\mathit{\text{value}}⟩$.
Constraint: ${\mathbf{lda}}\ge {\mathbf{m}}$.
On entry, ${\mathbf{sda}}=⟨\mathit{\text{value}}⟩$ and ${\mathbf{n}}=⟨\mathit{\text{value}}⟩$.
Constraint: ${\mathbf{sda}}\ge {\mathbf{n}}$.
${\mathbf{ifail}}=3$
On entry, ${\mathbf{lenc}}=⟨\mathit{\text{value}}⟩$.
Constraint: ${\mathbf{lenc}}\ge ⟨\mathit{\text{value}}⟩$, the total number of coefficents to be generated.
${\mathbf{ifail}}=5$
On entry, ${\mathbf{nwl}}=⟨\mathit{\text{value}}⟩$.
Constraint: ${\mathbf{nwl}}\ge 1$.
On entry, ${\mathbf{nwl}}=⟨\mathit{\text{value}}⟩$ and ${\mathbf{nwlmax}}=⟨\mathit{\text{value}}⟩$ in c09acf.
Constraint: ${\mathbf{nwl}}\le {\mathbf{nwlmax}}$ in c09acf.
${\mathbf{ifail}}=6$
Either the communication array icomm has been corrupted or there has not been a prior call to the initialization routine c09acf.
The initialization routine was called with ${\mathbf{wtrans}}=\text{'S'}$.
${\mathbf{ifail}}=-99$
See Section 7 in the Introduction to the NAG Library FL Interface for further information.
${\mathbf{ifail}}=-399$
Your licence key may have expired or may not have been installed correctly.
See Section 8 in the Introduction to the NAG Library FL Interface for further information.
${\mathbf{ifail}}=-999$
Dynamic memory allocation failed.
See Section 9 in the Introduction to the NAG Library FL Interface for further information.

## 7Accuracy

The accuracy of the wavelet transform depends only on the floating-point operations used in the convolution and downsampling and should thus be close to machine precision.

## 8Parallelism and Performance

c09fcf is not threaded in any implementation.

The example program shows how the wavelet coefficients at each level can be extracted from the output array c. Denoising can be carried out by applying a thresholding operation to the detail coefficients at every level. If ${c}_{ij}$ is a detail coefficient then ${\stackrel{^}{c}}_{ij}={c}_{ij}+\sigma {\epsilon }_{ij}$ and $\sigma {\epsilon }_{ij}$ is the transformed noise term. If some threshold parameter $\alpha$ is chosen, a simple hard thresholding rule can be applied as
 $c¯ ij = { 0, if ​ |c^ij| ≤ α c^ij , if ​ |c^ij| > α,$
taking ${\overline{c}}_{ij}$ to be an approximation to the required detail coefficient without noise, ${c}_{ij}$. The resulting coefficients can then be used as input to c09fdf in order to reconstruct the denoised signal.
See the references given in the introduction to this chapter for a more complete account of wavelet denoising and other applications.

## 10Example

This example computes the three-dimensional multi-level discrete wavelet decomposition for $7×6×5$ input data using the biorthogonal wavelet of order $1.1$ (set ${\mathbf{wavnam}}=\text{'BIOR1.1'}$ in c09acf) with periodic end extension, prints a selected set of wavelet coefficients and then reconstructs and verifies that the reconstruction matches the original data.

### 10.1Program Text

Program Text (c09fcfe.f90)

### 10.2Program Data

Program Data (c09fcfe.d)

### 10.3Program Results

Program Results (c09fcfe.r)