NAG Library Function Document

nag_idwt (c09cbc)

 Contents

    1  Purpose
    7  Accuracy
    10  Example

1
Purpose

nag_idwt (c09cbc) computes the inverse one-dimensional discrete wavelet transform (DWT) at a single level. The initialization function nag_wfilt (c09aac) must be called first to set up the DWT options.

2
Specification

#include <nag.h>
#include <nagc09.h>
void  nag_idwt (Integer lenc, const double ca[], const double cd[], Integer n, double y[], const Integer icomm[], NagError *fail)

3
Description

nag_idwt (c09cbc) performs the inverse operation of nag_dwt (c09cac). That is, given sets of nc approximation coefficients and detail coefficients, computed by nag_dwt (c09cac) using a DWT as set up by the initialization function nag_wfilt (c09aac), on a real data array of length n, nag_idwt (c09cbc) will reconstruct the data array yi, for i=1,2,,n, from which the coefficients were derived.

4
References

None.

5
Arguments

1:     lenc IntegerInput
On entry: the dimension of the arrays ca and cd.
Constraint: lencnc, where nc is the value returned in nwc by the call to the initialization function nag_wfilt (c09aac).
2:     ca[lenc] const doubleInput
On entry: the nc approximation coefficients, Ca. These will normally be the result of some transformation on the coefficients computed by nag_dwt (c09cac).
3:     cd[lenc] const doubleInput
On entry: the nc detail coefficients, Cd. These will normally be the result of some transformation on the coefficients computed by nag_dwt (c09cac).
4:     n IntegerInput
On entry: n, the length of the original data array from which the wavelet coefficients were computed by nag_dwt (c09cac) and the length of the data array y that is to be reconstructed by this function.
Constraint: This must be the same as the value n passed to the initialization function nag_wfilt (c09aac).
5:     y[n] doubleOutput
On exit: the reconstructed data based on approximation and detail coefficients Ca and Cd and the transform options supplied to the initialization function nag_wfilt (c09aac).
6:     icomm[100] const IntegerCommunication Array
On entry: contains details of the discrete wavelet transform and the problem dimension and, possibly, additional information on the previously computed forward transform.
7:     fail NagError *Input/Output
The NAG error argument (see Section 3.7 in How to Use the NAG Library and its Documentation).

6
Error Indicators and Warnings

NE_ALLOC_FAIL
Dynamic memory allocation failed.
See Section 2.3.1.2 in How to Use the NAG Library and its Documentation for further information.
NE_ARRAY_DIM_LEN
On entry, array dimension lenc not large enough: lenc=value but must be at least value.
NE_BAD_PARAM
On entry, argument value had an illegal value.
NE_INITIALIZATION
Either the initialization function has not been called first or array icomm has been corrupted.
Either the initialization function was called with wtrans=Nag_MultiLevel or array icomm has been corrupted.
On entry, n is inconsistent with the value passed to the initialization function: n=value, n should be value.
NE_INTERNAL_ERROR
An internal error has occurred in this function. Check the function call and any array sizes. If the call is correct then please contact NAG for assistance.
See Section 2.7.6 in How to Use the NAG Library and its Documentation for further information.
NE_NO_LICENCE
Your licence key may have expired or may not have been installed correctly.
See Section 2.7.5 in How to Use the NAG Library and its Documentation for further information.

7
Accuracy

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.

8
Parallelism and Performance

nag_idwt (c09cbc) is not threaded in any implementation.

9
Further Comments

None.

10
Example

See Section 10 in nag_dwt (c09cac).
© The Numerical Algorithms Group Ltd, Oxford, UK. 2017