# Kmulti.inhom

##### Inhomogeneous Marked K-Function

For a marked point pattern,
estimate the inhomogeneous version of the multitype \(K\) function
which counts the expected number of points of subset \(J\)
within a given distance from a typical point in subset `I`

,
adjusted for spatially varying intensity.

- Keywords
- spatial, nonparametric

##### Usage

```
Kmulti.inhom(X, I, J, lambdaI=NULL, lambdaJ=NULL,
…,
r=NULL, breaks=NULL,
correction=c("border", "isotropic", "Ripley", "translate"),
lambdaIJ=NULL,
sigma=NULL, varcov=NULL,
lambdaX=NULL, update=TRUE, leaveoneout=TRUE)
```

##### Arguments

- X
The observed point pattern, from which an estimate of the inhomogeneous multitype \(K\) function \(K_{IJ}(r)\) will be computed. It must be a marked point pattern. See under Details.

- I
Subset index specifying the points of

`X`

from which distances are measured. See Details.- J
Subset index specifying the points in

`X`

to which distances are measured. See Details.- lambdaI
Optional. Values of the estimated intensity of the sub-process

`X[I]`

. Either a pixel image (object of class`"im"`

), a numeric vector containing the intensity values at each of the points in`X[I]`

, a fitted point process model (object of class`"ppm"`

or`"kppm"`

or`"dppm"`

), or a`function(x,y)`

which can be evaluated to give the intensity value at any location,- lambdaJ
Optional. Values of the estimated intensity of the sub-process

`X[J]`

. Either a pixel image (object of class`"im"`

), a numeric vector containing the intensity values at each of the points in`X[J]`

, a fitted point process model (object of class`"ppm"`

or`"kppm"`

or`"dppm"`

), or a`function(x,y)`

which can be evaluated to give the intensity value at any location.- …
Ignored.

- r
Optional. Numeric vector. The values of the argument \(r\) at which the multitype \(K\) function \(K_{IJ}(r)\) should be evaluated. There is a sensible default. First-time users are strongly advised not to specify this argument. See below for important conditions on \(r\).

- breaks
This argument is for internal use only.

- correction
A character vector containing any selection of the options

`"border"`

,`"bord.modif"`

,`"isotropic"`

,`"Ripley"`

,`"translate"`

,`"none"`

or`"best"`

. It specifies the edge correction(s) to be applied. Alternatively`correction="all"`

selects all options.- lambdaIJ
Optional. A matrix containing estimates of the product of the intensities

`lambdaI`

and`lambdaJ`

for each pair of points, the first point belonging to subset`I`

and the second point to subset`J`

.- sigma,varcov
Optional arguments passed to

`density.ppp`

to control the smoothing bandwidth, when`lambda`

is estimated by kernel smoothing.- lambdaX
Optional. Values of the intensity for all points of

`X`

. Either a pixel image (object of class`"im"`

), a numeric vector containing the intensity values at each of the points in`X`

, a fitted point process model (object of class`"ppm"`

or`"kppm"`

or`"dppm"`

), or a`function(x,y)`

which can be evaluated to give the intensity value at any location. If present, this argument overrides both`lambdaI`

and`lambdaJ`

.- update
Logical value indicating what to do when

`lambdaI`

,`lambdaJ`

or`lambdaX`

is a fitted point process model (class`"ppm"`

,`"kppm"`

or`"dppm"`

). If`update=TRUE`

(the default), the model will first be refitted to the data`X`

(using`update.ppm`

or`update.kppm`

) before the fitted intensity is computed. If`update=FALSE`

, the fitted intensity of the model will be computed without re-fitting it to`X`

.- leaveoneout
Logical value (passed to

`density.ppp`

or`fitted.ppm`

) specifying whether to use a leave-one-out rule when calculating the intensity.

##### Details

The function `Kmulti.inhom`

is the counterpart, for spatially-inhomogeneous marked point patterns,
of the multitype \(K\) function `Kmulti`

.

Suppose \(X\) is a marked point process, with marks of any kind. Suppose \(X_I\), \(X_J\) are two sub-processes, possibly overlapping. Typically \(X_I\) would consist of those points of \(X\) whose marks lie in a specified range of mark values, and similarly for \(X_J\). Suppose that \(\lambda_I(u)\), \(\lambda_J(u)\) are the spatially-varying intensity functions of \(X_I\) and \(X_J\) respectively. Consider all the pairs of points \((u,v)\) in the point process \(X\) such that the first point \(u\) belongs to \(X_I\), the second point \(v\) belongs to \(X_J\), and the distance between \(u\) and \(v\) is less than a specified distance \(r\). Give this pair \((u,v)\) the numerical weight \(1/(\lambda_I(u)\lambda_J(u))\). Calculate the sum of these weights over all pairs of points as described. This sum (after appropriate edge-correction and normalisation) is the estimated inhomogeneous multitype \(K\) function.

The argument `X`

must be a point pattern (object of class
`"ppp"`

) or any data that are acceptable to `as.ppp`

.

The arguments `I`

and `J`

specify two subsets of the
point pattern. They may be any type of subset indices, for example,
logical vectors of length equal to `npoints(X)`

,
or integer vectors with entries in the range 1 to
`npoints(X)`

, or negative integer vectors.

Alternatively, `I`

and `J`

may be **functions**
that will be applied to the point pattern `X`

to obtain
index vectors. If `I`

is a function, then evaluating
`I(X)`

should yield a valid subset index. This option
is useful when generating simulation envelopes using
`envelope`

.

The argument `lambdaI`

supplies the values
of the intensity of the sub-process identified by index `I`

.
It may be either

- a pixel image
(object of class

`"im"`

) which gives the values of the intensity of`X[I]`

at all locations in the window containing`X`

;- a numeric vector
containing the values of the intensity of

`X[I]`

evaluated only at the data points of`X[I]`

. The length of this vector must equal the number of points in`X[I]`

.- a function
of the form

`function(x,y)`

which can be evaluated to give values of the intensity at any locations.- a fitted point process model
(object of class

`"ppm"`

,`"kppm"`

or`"dppm"`

) whose fitted*trend*can be used as the fitted intensity. (If`update=TRUE`

the model will first be refitted to the data`X`

before the trend is computed.)- omitted:
if

`lambdaI`

is omitted then it will be estimated using a leave-one-out kernel smoother.

If `lambdaI`

is omitted, then it will be estimated using
a `leave-one-out' kernel smoother, as described in Baddeley,
Moller
and Waagepetersen (2000). The estimate of `lambdaI`

for a given
point is computed by removing the point from the
point pattern, applying kernel smoothing to the remaining points using
`density.ppp`

, and evaluating the smoothed intensity
at the point in question. The smoothing kernel bandwidth is controlled
by the arguments `sigma`

and `varcov`

, which are passed to
`density.ppp`

along with any extra arguments.

Similarly `lambdaJ`

supplies the values
of the intensity of the sub-process identified by index `J`

.

Alternatively if the argument `lambdaX`

is given, then it specifies
the intensity values for all points of `X`

, and the
arguments `lambdaI`

, `lambdaJ`

will be ignored.

The argument `r`

is the vector of values for the
distance \(r\) at which \(K_{IJ}(r)\) should be evaluated.
It is also used to determine the breakpoints
(in the sense of `hist`

)
for the computation of histograms of distances.

First-time users would be strongly advised not to specify `r`

.
However, if it is specified, `r`

must satisfy `r[1] = 0`

,
and `max(r)`

must be larger than the radius of the largest disc
contained in the window.

Biases due to edge effects are
treated in the same manner as in `Kinhom`

.
The edge corrections implemented here are

- border
the border method or ``reduced sample'' estimator (see Ripley, 1988). This is the least efficient (statistically) and the fastest to compute. It can be computed for a window of arbitrary shape.

- isotropic/Ripley
Ripley's isotropic correction (see Ripley, 1988; Ohser, 1983). This is currently implemented only for rectangular windows.

- translate
Translation correction (Ohser, 1983). Implemented for all window geometries.

The pair correlation function `pcf`

can also be applied to the
result of `Kmulti.inhom`

.

##### Value

An object of class `"fv"`

(see `fv.object`

).

Essentially a data frame containing numeric columns

the values of the argument \(r\) at which the function \(K_{IJ}(r)\) has been estimated

the theoretical value of \(K_{IJ}(r)\) for a marked Poisson process, namely \(\pi r^2\)

##### References

Baddeley, A., Moller, J. and Waagepetersen, R. (2000)
Non- and semiparametric estimation of interaction in
inhomogeneous point patterns.
*Statistica Neerlandica* **54**, 329--350.

##### See Also

##### Examples

```
# NOT RUN {
# Finnish Pines data: marked by diameter and height
plot(finpines, which.marks="height")
II <- (marks(finpines)$height <= 2)
JJ <- (marks(finpines)$height > 3)
K <- Kmulti.inhom(finpines, II, JJ)
plot(K)
# functions determining subsets
f1 <- function(X) { marks(X)$height <= 2 }
f2 <- function(X) { marks(X)$height > 3 }
K <- Kmulti.inhom(finpines, f1, f2)
# }
```

*Documentation reproduced from package spatstat, version 1.55-1, License: GPL (>= 2)*