A temporal interaction function for use in twinstim
can be constructed via the tiaf function.
It checks the supplied function elements, assigns defaults for
missing arguments, and returns all checked arguments in a list.
However, for standard applications it is much easier to use one of the
pre-defined temporal interaction functions, e.g.,
tiaf.exponential.
tiaf(g, G, deriv, Deriv, npars, validpars = NULL)list of checked arguments.
the temporal interaction function. It must accept
two arguments, the first one being a vector of time points, the
second one a parameter vector. For marked twinstim, it must
accept the type of the event (integer code) as its third argument
(either a single type for all locations or separate types for each
location).
a primitive of \(g(t)\) (with respect to time). It must
accept the same arguments as g, for instance a vector
of time points (not just a single one).
optional derivative of \(g(t)\) with respect to
the parameters. It takes the same arguments as g but
returns a matrix with as many rows as there were time points in the
input and npars columns. This derivative is necessary for the
calculation of the score function in twinstim(), which is
advantageous for the numerical log-likelihood maximization.
optional primitive of deriv (with respect to
time). It must accept the same arguments as deriv, g and
G and returns a matrix with as many rows as there were time
points in the input and npars columns. The integrated
derivative is necessary for the score function in twinstim.
the number of parameters of the temporal interaction
function g (i.e. the length of its second argument).
optional function taking one argument, the parameter vector, indicating if it
is valid. This approach to specify parameter constraints is rarely
needed, because usual box-constrained parameters can be taken into
account by using L-BFGS-B as the optimization method in
twinstim (with arguments lower and upper), and
positivity constraints by using log-parametrizations.
This component is not necessary (and ignored) if npars == 0.
Sebastian Meyer
tiaf.exponential for a pre-defined temporal interaction
function, and siaf for the spatial interaction function.