.TH s.kcv
.SH NAME
\fIs.kcv\fR \- Randomly partition sites into test/train sets.
.br
.I (GRASS Sites Program)
.SH SYNOPSIS
\fBs.kcv\fR
.br
\fBs.kcv help\fR
.br
\fBs.kcv \fR[\fB-dq\fR] \fBk\*=value\fR \fBsites\*=\fIname\fR 
.SH DESCRIPTION
.I s.kcv
randomly divides a sites lists into 
.I k 
sets of test/train data (for \fBk\fR-fold \fBc\fRross \fBv\fRalidation).
Test partitions are mutually exclusive. That is, a site will
appear in only one test partition and 
.I k-1 
training partitions. 
.LP
The program generates a random point using the selected
random number generator and then finds the closest site to
it. This site is removed from the candidate list (meaning
that it will not be selected for any other test set) and
saved in the first test partition file.  This is repeated
until enough points have been selected for the test
partition.  The number of sites chosen for test partitions
depends upon the number of sites available and the number
of partitions chosen (this number is made as consistent as
possible while ensuring that all sites will be chosen for
testing). This process of filling up a test partition is
done
.I k
times.
.LP
\fBFlags:\fR
.IP \fB-d\fR 18
Use 
.I drand48() 
(default is 
.I rand()).
.IP \fB-q\fR 18
Quiet. Don't report progress.
.LP
\fBParameters:\fR
.IP \fBk\*=\fIvalue\fR 18
Positive integer value indicating the number of partitions.
.LP
.IP \fBsites\*=\fIname\fR 18
Name of a sites file to store random points in.
.LP
Test/train pairs are saved as sites list using 
.I name
as a basename. Test sites are saved in \fIname\fR-test.\fIi\fR
while training sites are saved in \fIname\fR-train.\fIi\fR,
where 
.I i
ranges from zero to
.I k.
.SH NOTES
Existing files are silently overwritten.
.LP
An ideal random sites generator will follow a Poisson
distribution. The merits of
.I rand()
versus
.I drand48()
in this respect are unknown.  Train/test partitions,
though, can only be as random as the original sites.
This program simply divides sites up in a random 
manner. 
.LP 
Be warned that random number generation
occurs over the intervals defined by the current
region.
.LP
This program may not work properly with Lat-long data.
.LP
.SH SEE ALSO
.I rand(3),
.I drand48(3),
.I s.rand
and
.I g.region
.SH BUGS
Please send all bug fixes and comments to the author.
.SH AUTHOR
James Darrell McCauley, Purdue University 
.if n .br 
(mccauley@ecn.purdue.edu)