Extract Quadrature Scheme Used to Fit a Point Process Model
Given a fitted point process model, this function extracts the quadrature scheme used to fit the model.
quad.ppm(object, drop=FALSE, clip=FALSE)
object |
fitted point process model (an object of class |
drop |
Logical value determining whether to delete quadrature points that were not used to fit the model. |
clip |
Logical value determining whether to erode the window,
if |
An object of class "ppm" represents a point process model
that has been fitted to data. It is typically produced by
the model-fitting algorithm ppm.
The maximum pseudolikelihood algorithm in ppm
approximates the pseudolikelihood
integral by a sum over a finite set of quadrature points,
which is constructed by augmenting
the original data point pattern by a set of “dummy” points.
The fitted model object returned by ppm
contains complete information about this quadrature scheme.
See ppm or ppm.object for further
information.
This function quad.ppm extracts the quadrature scheme.
A typical use of this function would be to inspect the quadrature scheme
(points and weights) to gauge the accuracy of the approximation to the
exact pseudolikelihood.
Some quadrature points may not have been used in
fitting the model. This happens if the border correction is used,
and in other cases (e.g. when the value of a covariate is NA
at these points). The argument drop specifies whether these
unused quadrature points shall be deleted (drop=TRUE) or
retained (drop=FALSE) in the return value.
The quadrature scheme has a window, which by default is set to
equal the window of the original data. However this window may be
larger than the actual domain of integration of the pseudolikelihood
or composite likelihood that was used to fit the model.
If clip=TRUE then the window of the quadrature scheme is
set to the actual domain of integration. This option only has an effect
when the model was fitted using the border correction; then
the window is obtained by eroding the original data window
by the border correction distance.
See ppm.object for a list of all operations that can be
performed on objects of class "ppm".
See quad.object for a list of all operations that can be
performed on objects of class "quad".
This function can also be applied to objects of class "kppm"
and "lppm".
A quadrature scheme (object of class "quad").
Adrian Baddeley Adrian.Baddeley@curtin.edu.au
and Rolf Turner r.turner@auckland.ac.nz
fit <- ppm(cells ~1, Strauss(r=0.1)) Q <- quad.ppm(fit) # plot(Q) npoints(Q$data) npoints(Q$dummy)
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