# rmhstart

##### Determine Initial State for Metropolis-Hastings Simulation.

Builds a description of the initial state for the Metropolis-Hastings algorithm.

##### Usage

```
rmhstart(start, …)
# S3 method for default
rmhstart(start=NULL, …, n.start=NULL, x.start=NULL)
```

##### Arguments

- start
An existing description of the initial state in some format. Incompatible with the arguments listed below.

- …
There should be no other arguments.

- n.start
Number of initial points (to be randomly generated). Incompatible with

`x.start`

.- x.start
Initial point pattern configuration. Incompatible with

`n.start`

.

##### Details

Simulated realisations of many point process models
can be generated using the Metropolis-Hastings algorithm
implemented in `rmh`

.

This function `rmhstart`

creates a full description of the initial state of the
Metropolis-Hastings algorithm,
*including possibly the initial state of the random number generator*,
for use in a subsequent call to `rmh`

. It also
checks that the initial state is valid.

The initial state should be specified **either** by the
first argument `start`

**or** by the other arguments
`n.start`

, `x.start`

etc.

If `start`

is a list, then it should have components named
`n.start`

or `x.start`

,
with the same interpretation as described below.

The arguments are:

- n.start
The number of “initial” points to be randomly (uniformly) generated in the simulation window

`w`

. Incompatible with`x.start`

.For a multitype point process,

`n.start`

may be a vector (of length equal to the number of types) giving the number of points of each type to be generated.If expansion of the simulation window is selected (see the argument

`expand`

to`rmhcontrol`

), then the actual number of starting points in the simulation will be`n.start`

multiplied by the expansion factor (ratio of the areas of the expanded window and original window).For faster convergence of the Metropolis-Hastings algorithm, the value of

`n.start`

should be roughly equal to (an educated guess at) the expected number of points for the point process inside the window.- x.start
Initial point pattern configuration. Incompatible with

`n.start`

.`x.start`

may be a point pattern (an object of class`ppp`

), or an object which can be coerced to this class by`as.ppp`

, or a dataset containing vectors`x`

and`y`

.If

`x.start`

is specified, then expansion of the simulation window (the argument`expand`

of`rmhcontrol`

) is not permitted.

The parameters `n.start`

and `x.start`

are
*incompatible*.

##### Value

An object of class `"rmhstart"`

, which is essentially
a list of parameters describing the initial point pattern
and (optionally) the initial state of the random number generator.

There is a `print`

method for this class, which prints
a sensible description of the initial state.

##### See Also

##### Examples

```
# NOT RUN {
# 30 random points
a <- rmhstart(n.start=30)
a
# a particular point pattern
b <- rmhstart(x.start=cells)
# }
```

*Documentation reproduced from package spatstat, version 1.63-0, License: GPL (>= 2)*