filter.select {wavethresh} | R Documentation

## Provide wavelet filter coefficients.

### Description

This function stores the filter coefficients necessary for doing a discrete wavelet transform (and its inverse).

### Usage

    filter.select(filter.number, family="DaubLeAsymm", constant=1)

### Arguments

`filter.number` | This selects the desired filter, an integer that takes a value dependent upon the family that you select.
`family` | This selects the basic family that the wavelet comes from. The choices are DaubExPhase for Daubechies' extremal phase wavelets, DaubLeAsymm for Daubechies' ``least-asymmetric'' wavelets, bolf{Lawton} for Lawton's complex-valued wavelets, LittlewoodPaley for a bad approximation to Littlewood-Paley wavelets.
`constant` | This constant is applied as a multiplier to all the coefficients. It can be a vector, and so you can adapt the filter coefficients to be whatever you want. (This is feature of negative utility, or ``there is less to this than meets the eye'' as my old PhD supervisor would say [GPN]).

### Details

This function contains at least three types of filter. Two types can be selected with family set to DaubExPhase, these wavelets are the Haar wavelet (selected by filter.number=1 within this family) and Daubechies ``extremal phase'' wavelets selected by filter.numbers ranging from 2 to 10). Setting family to DaubLeAsymm gives you Daubechies least asymmetric wavelets, but here the filter number ranges from 4 to 10. For Daubechies wavelets, filter.number corresponds to the N of that paper, the wavelets become more regular as the filter.number increases, but they are all of compact support.

Setting family equal to ``Lawton'' chooses complex-valued wavelets. The only wavelet available is the one with ``filter.number'' equal to 3.

The function `compare.filters` can be used to compare two filters.

### Value

Alist is returned with four components describing the filter:

`H` | A vector containing the filter coefficients.
`G` | A vector containing filter coefficients (if Lawton wavelets are selected, otherwise this is NULL).
`name` | A character string containing the name of the filter.
`family` | A character string containing the family of the filter.
`filter.number` | The filter number used to select the filter from within a family.

### RELEASE

Version 3.5.3 Copyright Guy Nason 1994

### Note

The (Daubechies) filter coefficients should always sum to sqrt(2). This is a useful check on their validity.

### See Also

`wd`, `wr`, `wr.wd`, `accessC`, `accessD`, `compare.filters`, `imwd`, `imwr`, `threshold`, `draw`.

### Examples

    #This function is usually called by others. However, on occasion you may wish to look at the coefficients themselves.

    #
    # look at the filter coefficients for N=4 (by default Daubechies'
    # least-asymmetric wavelets.)
    #
    #filter.select(4)
    #$H:
    #[1] -0.07576571 -0.02963553  0.49761867  0.80373875  0.29785780
    #[6] -0.09921954 -0.01260397  0.03222310
    #
    #$G:
    #NULL
    #
    #$name:
    #[1] "Daub cmpct on least asymm N=4"
    #
    #$family:
    #[1] "DaubLeAsymm"
    #
    #$filter.number:
    #[1] 4

[Package wavethresh version 4.0-2 Index]