Lab 7: Envelopes and Monte Carlo tests

This session is concerned with evelopes of summary statistics and Monte Carlo tests.
The lecturer’s R script is available here (right click and save).

Exercise 1

For the swedishpines data:

1. Plot the \(K\) function along with pointwise envelopes from 39 simulations of CSR:

   plot(envelope(swedishpines, Kest, nsim=39))

2. Plot the \(L\) function along with pointwise envelopes from 39 simulations of CSR.

3. Plot the \(L\) function along with simultaneous envelopes from 19 simulations of CSR, using ginterval=c(0,0.5).

4. Plot the \(L\) function for along with simultaneous envelopes from 99 simulations of CSR using ginterval=c(0,0.5). What is the significance level of the associated test?

Exercise 2

To understand the difficulties with the \(K\)-function when the point pattern is not spatially homogeneous, try the following experiment (like in the previous lab session).

1. Generate a simulated realisation of an inhomogeneous Poisson process, e.g.

   X <- rpoispp(function(x,y){ 200 * exp(-3 * x) })

2. Compute simulation envelopes (of your favorite type) of the \(K\)- or \(L\)-function under CSR. They may well indicate significant departure from CSR.

3. Fit a Poisson point process model to the japanesepines data with log-quadratic trend (formula ~polynom(x,y,2)). Plot the \(L\)-function of the data along with simultaneous envelopes from 99 simulations of the fitted model.