XploRe Help : SPKRsemat

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 SPKRcorrelogram SPKRvariogram SPKRmultcontours

Quantlet:		SPKRsemat
Description:		evaluates a Kriging standard error of prediction surface over a grid

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 = SPKRsemat (obj, xl, xu, yl, yu, n {, se})`
Input:
	`obj`	list, (of type "trgls") calculated by SPKRsurfgls
	`xl`	scalar, lower limit in x-direction of the rectangle for grid
	`xu`	scalar, upper limit in x-direction of the rectangle for grid
	`yl`	scalar, lower limit in y-direction of the rectangle for grid
	`yu`	scalar, upper limit in y-direction of the rectangle for grid
	`n`	scalar, used to create a n x n grid within the rectangle
	`se`	optional scalar, standard error at distance zero as a multiple of the supplied covariance; if omitted, estimated under the assumption that a correlation function has been applied before
Output:
	`res`	list, consisting of components z, xl, xu, yl, yu, n and type for further usage with SPKRmultcontours:
	`res.z`	(n+1)^2 x 3 matrix, grid
	`xl`	scalar, same as input value xl
	`xu`	scalar, same as input value xu
	`yl`	scalar, same as input value yl
	`yu`	scalar, same as input value yu
	`n`	scalar, same as input value n
	`type`	string, "semat"

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 trend surface of order 2, using expcov as ; spatial covariance function with dval = 0.7, alph = 0, ; and se = 1 myres = SPKRsurfgls(2, 0, topo, 1000, 0.7, 0, 1) ; calculates a 30 x 30 grid within [0, 6.5] x [0, 6.5] ; using trend surface myres mygrid = SPKRsemat(myres, 0, 6.5, 0, 6.5, 30) mygrid

Result:

A grid suitable for display through SPKRmultcontours:

Contents of mygrid.z
[  1,]        0        0   31.116
[  2,]  0.21667        0   28.404
[  3,]  0.43333        0   26.577
[  4,]     0.65        0   25.693
[  5,]  0.86667        0   24.611
...

Contents of mygrid.xl
[1,]        0

Contents of mygrid.xu
[1,]      6.5

Contents of mygrid.yl
[1,]        0

Contents of mygrid.yu
[1,]      6.5

Contents of mygrid.n
[1,]       30

Contents of mygrid.type
[1,] "semat"

Author: J. Symanzik, 20000725 license MD*Tech