Set Domain for Spatial Point Pattern Analyses

Sets the rectangular domain `(xl, xu)' , `(yl, yu)'.

Syntax
	ppregion(xl=0, xu=1, yl=0, yu=1)
Input
xl Either `xl' or a list containing components `xl', `xu', `yl', `yu' (such as
a point-process object)
 xu
 yl
 yu

Output
none

Side effects
initializes variables in the `C' subroutines.

See also
`ppinit', `ppgetregion'