# dtwWindowingFunctions

##### Global constraints and windowing functions for DTW

Various global constraints (windows) which can be applied to
the `window.type`

argument of `dtw`

,
including the Sakoe-Chiba band, the Itakura parallelogram,
and custom functions.

- Keywords
- ts

##### Usage

```
noWindow(iw, jw, ...);
sakoeChibaWindow(iw,jw, window.size,...);
slantedBandWindow(iw,jw,query.size,reference.size, window.size,...);
itakuraWindow(iw,jw,query.size,reference.size, ...);
```dtwWindow.plot(fun,query.size=200,reference.size=220,...);

##### Arguments

- iw
index in the query (row) -- automatically set

- jw
index in the reference (column) -- automatically set

- query.size
size of the query time series -- automatically set

- reference.size
size of the reference time series -- automatically set

- window.size
window size, used by some windowing functions -- must be set

- fun
a windowing function

- ...
additional arguments passed to windowing functions

##### Details

Windowing functions can be passed to the
`window.type`

argument in `dtw`

to put a global
constraint to the warping paths allowed. They take two integer
arguments (plus optional parameters) and must return a boolean value
`TRUE`

if the coordinates fall within the allowed region
for warping paths, `FALSE`

otherwise.

User-defined functions can read variables `reference.size`

,
`query.size`

and `window.size`

; these are pre-set upon
invocation. Some functions require additional parameters which must
be set (e.g. `window.size`

). User-defined functions are free to
implement any window shape, as long as at least one path is allowed
between the initial and final alignment points, i.e., they are
compatible with the DTW constraints.

The `sakoeChibaWindow`

function implements the Sakoe-Chiba band,
i.e. `window.size`

elements around the `main`

diagonal. If
the window size is too small, i.e. if
`reference.size`

-`query.size`

> `window.size`

, warping
becomes impossible.

An `itakuraWindow`

global constraint is still provided with this
package. See example below for a demonstration of
the difference between a local the two.

The `slantedBandWindow`

(package-specific) is a band centered
around the (jagged) line segment which joins element `[1,1]`

to
element `[query.size,reference.size]`

, and will be
`window.size`

columns wide. In other words, the "diagonal" goes
from one corner to the other of the possibly rectangular cost matrix,
therefore having a slope of `M/N`

, not 1.

`dtwWindow.plot`

visualizes a windowing function. By default
it plots a 200 x 220 rectangular region, which can
be changed via `reference.size`

and `query.size`

arguments.

##### Value

Windowing functions return `TRUE`

if the coordinates passed as
arguments fall within the chosen warping window, `FALSE`

otherwise. User-defined functions should do the same.

##### Note

Although `dtwWindow.plot`

resembles object-oriented notation,
there is not a such a dtwWindow class currently.

A widely held misconception is that the "Itakura parallelogram" (as
described in reference [2]) is a *global* constraint, i.e. a
window. To the author's knowledge, it instead arises from the local
slope restrictions imposed to the warping path, such as the one
implemented by the `typeIIIc`

step pattern.

##### References

[1] Sakoe, H.; Chiba, S., *Dynamic programming algorithm optimization for spoken word recognition,*
Acoustics, Speech, and Signal Processing [see also IEEE Transactions on Signal Processing], IEEE Transactions on ,
vol.26, no.1, pp. 43-49, Feb 1978 URL: http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=1163055

[2] Itakura, F., *Minimum prediction residual principle applied to speech
recognition,* Acoustics, Speech, and Signal Processing [see also IEEE
Transactions on Signal Processing], IEEE Transactions on , vol.23, no.1, pp.
67-72, Feb 1975. URL: http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=1162641

##### Examples

`library(dtw)`

```
# NOT RUN {
## Display some windowing functions
dtwWindow.plot(itakuraWindow, main="So-called Itakura parallelogram window")
dtwWindow.plot(slantedBandWindow, window.size=2,
reference=13, query=17, main="The slantedBandWindow at window.size=2")
## Asymmetric step with Sakoe-Chiba band
idx<-seq(0,6.28,len=100);
query<-sin(idx)+runif(100)/10;
reference<-cos(idx);
asyband<-dtw(query,reference,keep=TRUE,
step=asymmetric,
window.type=sakoeChibaWindow,
window.size=30 );
dtwPlot(asyband,type="density",main="Sine/cosine: asymmetric step, S-C window")
# }
```

*Documentation reproduced from package dtw, version 1.18-1, License: GPL (>= 2)*