Computes feature of a time series based on tiled (non-overlapping) windows.
Means or variances are produced for all tiled windows. Then stability is
the variance of the means, while lumpiness is the variance of the variances.

```
var_tiled_var(x, .size = NULL, .period = 1)
var_tiled_mean(x, .size = NULL, .period = 1)
```

## Arguments

- x
a univariate time series

- .size
size of sliding window, if NULL `.size`

will be automatically chosen using `.period`

- .period
The seasonal period (optional)

## Value

A numeric vector of length 2 containing a measure of lumpiness and
a measure of stability.

## Author

Earo Wang and Rob J Hyndman