Proxy functions for Monte Carlo sampling methods in sampSurf
Description
These functions encapsulate the proxy capabilities under Monte Carlo
sampling within "Stem
" subclass objects for the
estimation of volume.
Usage
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Arguments
proxy 
A character argument specifying the name of the proxy function to retrieve. 
stem 
An object that is a subclass of
" 
u.s 
The uniform (0,1) random number vector for Monte Carlo sampling to determine the sampled heights for the respective method. 
segBnds 
A vector of length two giving the lower and upper height/length bounds for volume estimation within the bole. These bounds correspond to the limits of integration along the bole. 
solidTypeProxy 
The applicable values for this and what they do
depend on whether the default sampSurf taper equation was used
to construct the 
truncateProxyStem 

wbProxySolve 
The two options specify which method is used to
numerically solve for the proxy heights. The default should normally
be used, the 
warningsOn 

... 
Used to ignore extraneious arguments passed at present. 
Details
The first function, getProxy
, returns one of the builtin proxy
functions from the sampSurf namespace so that it can be used
within the respective Monte Carlo sampling method. In the case of a
user proxy, it will also look for the proxy within the user's
workspace. The function does a number of checks for the minimal format
of “proxy” functions that are described in the vignette
reference below. Therefore, it will catch problems with arguments and
return lists in userdefined proxies. This is necessary to make sure
all userwritten proxy functions accept and return the standard set of
arguments and list components.
The builtin proxy functions are discussed in detail in the vignette. The builtin proxies range from very simple to fairly complex. They include...
cmcProxy
: This is the default proxy used for crude Monte Carlo
sampling in the crudeMonteCarlo
object constructor. It
is also used in control variate sampling in the
controlVariate
constructor for selecting the
height/length sample points.
gvProxy
: This is a simple proxy that is proportional to
crosssectional area at a given sampled height. It is the default
proxy used in importanceSampling
and
controlVariate
(as the proxy crosssectional area model)
methods for creation of their respective objects. Details on its uses
and potential concerns are found in the vignette.
wbProxy
: This proxy uses the default taper equation in
sampSurf. This is a much more complicated proxy than the other
two, and can take more arguments. It can be used in both importanceSampling
and
controlVariate
methods for determination of the sample
heights and crosssectional areas. Please see the vignette below for
details on this function and its use.
Value
getProxy
returns the proxy function. The other functions return a
list of the form...
g 
The function (closure) that actually determines the crosssectional area at a given height. 
G 
The volume integral for the stem segment. 
hgt.s 
The sampled heights along the bole segment at which

Please see the vignette for more details.
Author(s)
Jeffrey H. Gove
References
Gove, J. H. 2013. Monte Carlo sampling methods in sampSurf. Package vignette.
See Also
MonteCarloSampling
,
crudeMonteCarlo
,
importanceSampling
,
controlVariate
,
antitheticSampling
.
Examples
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