**smth9**

`smth9(`*expr*)

Performs a 9 point smoothing to the gridded result of the
*expr*

.

### Usage Notes

- The result at each grid point is a weighted average of the grid point
plus the 8 surrounding points. The center point receives a wieght of 1.0,
the points at each side and above and below receive a weight of 0.5, and
corner points receive a weight of 0.3.

- All 9 points are multiplied by their weights and summed, then divided
by the total weight to obtain the smoothed value. Any missing data points
are not included in the sum; points beyond the grid boundary are
considered to be missing. Thus the final result may be the result of an
averaging with less than 9 points.

- If the gridded data is 1-Dimensional, the result is a 3 point
smoothing.

### Examples