Define a region of interest on a graph or graphs.

Select the region, there are 5.

Select the type of region:

- Inside polygon
- Points inside a closed, non-intersecting polygon are considered inside
the region.
- Outside polygon
- Points outside a closed, non-intersecting polygon are considered
inside the region.
- Above, below, to the left, and to the right
- Regions defining a half-plane, points inside the half-plane are considered in the region.

Select the type of linkage, either a particular graph or all graphs, the default is the current graph.

Press **Accept** to make the pointer ready for the region definition.
In the polygonal region type, define the region by successive clicks with
the left mouse button, use the right mouse button to register the polygon.
In the line case, define the line by clicking on the beginning point and
end point of the line.

Evaluate an expression applied to points within a region.

Select the region to use.

Enter the expression, regions are referred to by Rn.x or Rn.y where `n' is the number of the region to use. Functions available are the same as those in `Evaluate expressions' described above.

Examples:

R0.X = R0.X - 1

Remove a defined region.

Select the region to remove and press `Apply'.

Extract points from a region to a set

Select the region to use.

Select the set to receive the points.

Select the graph to put the set.

Click on **Accept** to combine all points within the
specified region to the specified set and graph.

Delete points in a region.

Select the region to use.

Click on **Accept** to delete all points in all sets within
the specified region.

Compute the area and perimeter of a region. This item doesn't belong here as it
does not use the region structures. Click on **Area** or **Perimeter**
and use the mouse to define the region. The area or perimeter will be
displayed in the text items **Area = ** or **Perimeter = ** whichever
the case may be. Use the right mouse button to close the region.