an object of the class likfit, typically an
output of the function likfit.
geodata
a list containing elements coords and
data described next. Typically an object of the class
"geodata" - a geoR data-set. If not provided the arguments
coords and data must be provided instead.
coords
an n x 2 matrix containing in each row Euclidean
coordinates of the n data locations. By default it takes the
element coords of the argument geodata.
data
a vector with data values. By default it takes the
element data of the argument geodata.
sill.values
set of values of the partial sill parameter
sigma^2 for which the profile likelihood will be
computed.
range.values
set of values of the range parameter
phi for which the profile likelihood will be computed.
nugget.values
set of values of the nugget parameter
tau^2 for which the profile likelihood will be
computed. Only used if the model was fitted using the function
likfit with the option fix.nugget = FALSE.
nugget.rel.values
set of values of the relative nugget parameter
tauR^2 for which the profile likelihood will be
computed. Only used if the model was fitted using the function
likfit with the option fix.nugget = FALSE.
lambda.values
set of values of the Box-Cox transformation parameter
lambda for which the profile likelihood will be
computed. Only to be used if the model was fitted using the function
likfit with the option fix.lambda = FALSE.
sillrange.values
logical indicating
whether or not the 2-D profile likelihood should be computed.
Only valid if uni.only = FALSE.
sillnugget.values
as above.
rangenugget.values
as above.
sillnugget.rel.values
as above.
rangenugget.rel.values
as above.
silllambda.values
as above.
rangelambda.values
as above.
nuggetlambda.values
as above.
nugget.rellambda.values
as above.
uni.only
as above.
bi.only
as above.
messages
logical. Indicates whether
status messages should be printed on the screen (i.e. current output device)
while the function is running.
...
additional parameters to be passed to the minimization
function.
Details
The functions .proflik.* are auxiliary functions used to
compute the profile likelihoods. These functions are
internally called by the
minimization functions when estimating the model parameters.
Value
An object of the class "proflik" which is
a list. Each element contains values of a parameter (or a pair of
parameters for 2-D profiles) and the
corresponding value of the profile likelihood.
The components of the output will vary according to the
input options.
Note
Profile likelihoods for Gaussian Random Fields are usually
uni-modal.
Unusual or jagged shapes can
be due to the lack of the convergence in the numerical minimization
for particular values of the parameter(s).
If this is the case it might be necessary to pass control arguments
to the minimization functions using the argument ....
It's also advisable to try the different options for the
minimisation.function argument.
See documentation of the functions optim and/or
nlm for further details.
2-D profiles can be computed by setting the argument
uni.only = FALSE. However, before computing 2-D profiles be
sure they are really necessary.
Their computation can be time demanding since it
is performed on a grid determined by the
cross-product of the values defining the 1-D profiles.
There is no "default strategy" to find reasonable values for the
x-axis.
They must be found in a "try-and-error" exercise. It's recommended
to use short sequences in the initial attempts.
The EXAMPLE section below illustrates this.