# deriv.fv

##### Calculate Derivative of Function Values

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

- Keywords
- spatial, math, nonparametric

##### Usage

```
# S3 method for fv
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.

##### 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.

##### Value

Another function value table (object of class `"fv"`

)
of the same format.

##### See Also

##### Examples

```
# NOT RUN {
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)
# }
```

*Documentation reproduced from package spatstat, version 1.57-1, License: GPL (>= 2)*