Semi-variogram for regularly spaced data in one dimension
variog yvar [if exp] [in range] [, generate(newvar) lags(#)} list graph_options ]
Description
variog calculates, graphs, and optionally lists the first lags values of the semi-variogram for a regularly spaced series of observations in one spatial or temporal dimension. Data are assumed to be in the correct sort order, i.e. to be in spatial or temporal sequence.
The semi-variogram is a plot of the semi-variance
1 n - h 2 -------- SUM (y - y ) = gamma(h) 2(n - h) i = 1 i i + h
against the lag h = 1, ... , lags. In words, it shows half the mean difference squared at various lags. Note that the units of the semi-variogram are the units of the response variable, squared.
Options
generate(newvar) saves the semi-variances in newvar.
lags() specifies the number of lags. If not specified, the first int(_N/2) semi-variances are graphed: that is, the number of lags is about half the number of observations.
list lists out the semi-variances and the number of pairs of measurements on which they are based. This may help in identifying parts of the variogram based on rather few pairs of data.
graph_options refers to any of the options of line.
Examples
. variog height . variog height, list . variog height, recast(scatter)
Author
Nicholas J. Cox, University of Durham, U.K. n.j.cox@durham.ac.uk
Also see
On-line: help for variog2