Wavelet Toolbox |

**Syntax **

Y = dyaddown(X,EVENODD) Y = dyaddown(X) Y = dyaddown(X,EVENODD,'

') Y = dyaddown(X,'*type*

',EVENODD)*type*

**Description **

`Y = dyaddown(X,`

EVENODD`)`

where `X`

is a *vector*, returns a version of `X`

that has been downsampled by 2. Whether `Y`

contains the even- or odd-indexed samples of `X`

depends on the value of positive integer `EVENODD`

:

`Y = dyaddown(X)`

is equivalent to `Y = dyaddown(X,`

0`) `

(even-indexed samples).

`Y = dyaddown(X,`

EVENODD,'

'*type*`)`

or `Y = dyaddown(X,`

'

',EVENODD*type*`)`

, where `X`

is a *matrix*, returns a version of `X`

obtained by suppressing one out of two:

Columns of `X` |
If `'`
`'` = `'c'` |

Rows of `X` |
If `'`
`'` = `'r'` |

Rows and columns of `X` |
If `'`
`'` = `'m'` |

according to the parameter EVENODD, which is as above.

If you omit the `EVENODD`

or '

' arguments, *type*`dyaddown`

defaults to `EVENODD = 0 `

(even-indexed samples) and `'`

*type*`' = 'c'`

(columns).

`Y = dyaddown(X)`

is equivalent to `Y = dyaddown(X,`

0`,'c')`

. `Y = dyaddown(X`

,'

'*type*`)`

is equivalent to `Y = dyaddown(X,`

0`,`

'

'*type*`)`

. `Y = dyaddown(X,`

EVENODD`)`

is equivalent to `Y = dyaddown(X,`

EVENODD`,`

'

'*c*`)`

.

**Examples**

% For a vector. s = 1:10 s = 1 2 3 4 5 6 7 8 9 10 dse = dyaddown(s) % Downsample elements with even indices. dse = 2 4 6 8 10 % or equivalently dse = dyaddown(s,0) dse = 2 4 6 8 10 dso = dyaddown(s,1) % Downsample elements with odd indices. dso = 1 3 5 7 9 % For a matrix. s = (1:3)'*(1:4) s = 1 2 3 4 2 4 6 8 3 6 9 12 dec = dyaddown(s,0,'c') % Downsample columns with even indices. dec = 2 4 4 8 6 12 der = dyaddown(s,1,'r') % Downsample rows with odd indices. der = 1 2 3 4 3 6 9 12 dem = dyaddown(s,1,'m') % Downsample rows and columns % with odd indices. dem = 1 3 3 9

**See Also**

```
dyadup
```

**References **

Strang, G.; T. Nguyen (1996), *Wavelets and Filter Banks*, Wellesley-Cambridge Press.

dwtmode | dyadup |