XploRe Help : SPKRvariogram

Keywords - Function groups - @ A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Library:	spatial
See also:	SPKRsurfls SPKRsurfgls SPKRexpcov SPKRgaucov SPKRsphercov SPKRtrmat SPKRprmat SPKRsemat SPKRcorrelogram SPKRmultcontours

Quantlet:		SPKRvariogram
Description:		computes spatial (semi-)variograms of spatial data or residuals. Initially, it divides the range of the data into nint bins, and computes the average squared difference for pairs with separation in each bin. It returns results only for bins with 6 or more pairs.

Reference(s):

Venables, W. N., Ripley, B. D. (1999): Modern Applied Statistics with S-Plus, Third Edition, Springer, New York

Link:

Tutorial: Spatial statistics

Usage:	`res = SPKRvariogram (krig, nint)`
Input:
	`krig`	list, (of type "trls" or "trgls") calculated by SPKRsurfls or SPKRsurfgls
	`nint`	scalar, number of bins to be used
Output:
	`res`	list, consisting of components xpres, ypres and cntres:
	`res.xpres`	n x 1 vector, x coordinates of the variogram
	`res.ypres`	n x 1 vector, y coordinates of the variogram
	`res.cntres`	n x 1 vector, number of pairs averaged per bin

Note:

C-Code from Venables, Ripley (1999) forms the basis of this quantlet. Also check this reference for more details.

Example:

; loads the spatial statistics library library("spatial") ; reads a spatial data set topo = read("topo.dat") ; calculates a polynomial regression surface of order 2 myres = SPKRsurfls(2, topo) ; calculates the correlogram, using 25 bins varres = SPKRvariogram(myres, 25) varres

Result:

A list consisting of x and y coordinates of the variogram
and the number of pairs averaged per bin:

Contents of varres.xpres
[ 1,]        0
[ 2,]  0.34483
[ 3,]  0.68966
...
[20,]   6.5517
[21,]   6.8966

Contents of varres.ypres
[ 1,]        0
[ 2,]   197.78
[ 3,]   270.09
...
[20,]   1127.3
[21,]   1135.2

Contents of varres.cntres
[ 1,]        0
[ 2,]       18
[ 3,]       56
...
[20,]       17
[21,]        8

Author: J. Symanzik, 20000725 license MD*Tech