spatstat (version 1.48-0)

deriv.fv: Calculate Derivative of Function Values

Description

Applies numerical differentiation to the values in selected columns of a function value table.

Usage

"deriv"(expr, which = "*", ..., method=c("spline", "numeric"), kinks=NULL, periodic=FALSE, Dperiodic=periodic)

Arguments

expr

Function values to be differentiated. A function value table (object of class "fv", see fv.object).

which

Character vector identifying which columns of the table should be differentiated. Either a vector containing names of columns, or one of the wildcard strings "*" or "." explained below.

...

Extra arguments passed to smooth.spline to control the differentiation algorithm, if method="spline".

method

Differentiation method. A character string, partially matched to either "spline" or "numeric".

kinks

Optional vector of $x$ values where the derivative is allowed to be discontinuous.

periodic

Logical value indicating whether the function expr is periodic.

Dperiodic

Logical value indicating whether the resulting derivative should be a periodic function.

Value

Another function value table (object of class "fv") of the same format.

Details

This command performs numerical differentiation on the function values in a function value table (object of class "fv"). The differentiation is performed either by smooth.spline or by a naive numerical difference algorithm.

The command deriv is generic. This is the method for objects of class "fv".

Differentiation is applied to every column (or to each of the selected columns) of function values in turn, using the function argument as the $x$ coordinate and the selected column as the $y$ coordinate. The original function values are then replaced by the corresponding derivatives.

The optional argument which specifies which of the columns of function values in expr will be differentiated. The default (indicated by the wildcard which="*") is to differentiate all function values, i.e.\ all columns except the function argument. Alternatively which="." designates the subset of function values that are displayed in the default plot. Alternatively which can be a character vector containing the names of columns of expr.

If the argument kinks is given, it should be a numeric vector giving the discontinuity points of the function: the value or values of the function argument at which the function is not differentiable. Differentiation will be performed separately on intervals between the discontinuity points.

If periodic=TRUE then the function expr is taken to be periodic, with period equal to the range of the function argument in expr. The resulting derivative is periodic.

If periodic=FALSE but Dperiodic=TRUE, then the derivative is assumed to be periodic. This would be appropriate if expr is the cumulative distribution function of an angular variable, for example.

See Also

with.fv, fv.object, smooth.spline

Examples

   G <- Gest(cells)
   plot(deriv(G, which=".", spar=0.5))
   A <- pairorient(redwood, 0.05, 0.15)
   DA <- deriv(A, spar=0.6, Dperiodic=TRUE)