simulate.kppm: Simulate a Fitted Cluster Point Process Model

In spatstat.model: Parametric Statistical Modelling and Inference for the 'spatstat' Family

Simulate a Fitted Cluster Point Process Model

Description

Generates simulated realisations from a fitted cluster point process model.

Usage

  ## S3 method for class 'kppm'
simulate(object, nsim = 1, seed=NULL, ...,
         window=NULL, covariates=NULL,
         n.cond = NULL, w.cond = NULL,
         verbose=TRUE, retry=10,
         drop=FALSE)

Arguments

object	Fitted cluster point process model. An object of class "kppm".
nsim	Number of simulated realisations.
seed	an object specifying whether and how to initialise the random number generator. Either NULL or an integer that will be used in a call to set.seed before simulating the point patterns.
...	Additional arguments passed to the relevant random generator. See Details.
window	Optional. Window (object of class "owin") in which the model should be simulated.
covariates	Optional. A named list containing new values for the covariates in the model.
n.cond	Optional. Integer specifying a fixed number of points. See the section on Conditional Simulation.
w.cond	Optional. Conditioning region. A window (object of class "owin") specifying the region which must contain exactly n.cond points. See the section on Conditional Simulation.
verbose	Logical. Whether to print progress reports (when nsim > 1).
retry	Number of times to repeat the simulation if it fails (e.g. because of insufficient memory).
drop	Logical. If nsim=1 and drop=TRUE, the result will be a point pattern, rather than a list containing a point pattern.

Details

This function is a method for the generic function simulate for the class "kppm" of fitted cluster point process models.

Simulations are performed by rThomas, rMatClust, rCauchy, rVarGamma or rLGCP depending on the model.

Additional arguments ... are passed to the relevant function performing the simulation. For example the argument saveLambda is recognised by all of the simulation functions.

The return value is a list of point patterns. It also carries an attribute "seed" that captures the initial state of the random number generator. This follows the convention used in simulate.lm (see simulate). It can be used to force a sequence of simulations to be repeated exactly, as shown in the examples for simulate.

Value

A list of length nsim containing simulated point patterns (objects of class "ppp"). (For conditional simulation, the length of the result may be shorter than nsim).

The return value also carries an attribute "seed" that captures the initial state of the random number generator. See Details.

Conditional Simulation

If n.cond is specified, it should be a single integer. Simulation will be conditional on the event that the pattern contains exactly n.cond points (or contains exactly n.cond points inside the region w.cond if it is given).

Conditional simulation uses the rejection algorithm described in Section 6.2 of Moller, Syversveen and Waagepetersen (1998). There is a maximum number of proposals which will be attempted. Consequently the return value may contain fewer than nsim point patterns.

Warning: new implementation for LGCP

The simulation algorithm for log-Gaussian Cox processes has been completely re-written in spatstat.random version 3.2-0 to avoid depending on the package RandomFields which is now defunct (and is sadly missed).

It is no longer possible to replicate results of simulate.kppm for log-Gaussian Cox processes that were obtained using previous versions of spatstat.random.

The current code for simulating log-Gaussian Cox processes is a new implementation and should be considered vulnerable to new bugs.

Author(s)

\spatstatAuthors

References

\baddrubaturnbook \Moller

, J., Syversveen, A. and Waagepetersen, R. (1998) Log Gaussian Cox Processes. Scandinavian Journal of Statistics 25, 451–482.

See Also

kppm, rThomas, rMatClust, rCauchy, rVarGamma, rLGCP, simulate.ppm, simulate

Examples

  if(offline <- !interactive()) {
    spatstat.options(npixel=32, ndummy.min=16)
  }

  fit <- kppm(redwood ~x, "Thomas")
  simulate(fit, 2)

  simulate(fit, n.cond=60)

  if(offline) reset.spatstat.options()

spatstat.model documentation built on Sept. 30, 2024, 9:26 a.m.