ASReml-S reference manual - VSN International

4.4 Variance model functions 45inita vector of initial parameter values. This vector can have an optional namesattribute to set the boundary constraint for each parameter. In this case, thename of each element may be one of ”P”, ”U” or ”F” for positive, unconstrainedor fixed, respectively.modelnumber of parameters(f) form: f() fv() fh()exp 1 2 1 + ngau 1 2 1 + niexp 1 2 1 + nigau 1 2 1 + nieuc 1 2 1 + nsph 1 2 1 + ncir 1 2 1 + naexp 2 3 2 + nagau 2 3 2 + nphi the range paraeter. Default: φ = NA.nu the smoothness parameter. Default: ν = 0.5.delta governs geoetric anisotropy. Default: δ = 1.0.alpha governs geoetric anisotropy. Default: α = 0.0.lambda specifies the choice of metric. Default: λ = 2 for Euclidean distance.DetailsFor the Matérn function, if an argument is numeric, it is treated as a startingvalue for estimation and given the constraint code P (positive). This behaviourcan be altered by concatenating the numeric value followed by the constraintcode (P, U or F) into a character string. If an argument is absent from the call,the corresponding parameter is held fixed at its default value.Kriging models apply to points in an irregular (or regular) spatial grid. They require thespecification of the data coordinates to calculate pairwise distances. For example,• the distance between time points in a one-dimensional longitudinal analysis,• the spatial distance between plot coordinates in a two-dimensional field trial analysis,Distance information for power models is obtained from the object(s) or arguments passedto the relevant special function.For one dimensional models, the distances are obtained from one of:1. unique(x) where x is the required argument to the model function identifying the fieldin the data frame containing the points..2. the dist argument to the model function3. the pwrpoints list argument to asreml.control() (Section 7.1.1)For two dimensional models, the special functions require two arguments nominatingfields in the data frame specifying the (x, y) coordinates of each observation. For example,in the analysis of spatial data, if the x coordinate was in a variate row and the y coordinatewas in a variate labelled column, an anisotropic exponential model could be fitted byaexp(row, column).Note that for an R structure the data order is assumed correct, otherwise an error isgenerated.