lmfor (version 1.6)

ddcomp: Evaluate the fit of a tree diameter distribution

Description

A function to compare the fit of the observed tree diameter data (d) to a specified diameter distribution (density).

Usage

ddcomp(d,density="dweibull",power=0,limits=seq(0,100),limitsd=limits,plot=FALSE,...)

Arguments

d

numeric vector of observed diameters

density

either a valid name for a probability density function in R or a vector of diameter class densities for diameter classes whose limits are given in vector limitsd

power

the weight used in error index. Value 2 gives BA weight, 0 (default) the unweighted

limits

the diameter class limits to compute the error index

limitsd

see the description of argument density

plot

logical. Should a graph be produced to illustrate the ecdf of d and the cdf corresponding to density

...

additional arguments passed to function specified by a character-type density. e.g. Weibull shape and scale of if density="dweibull"

Value

A list of components

mudif

The difference in means

vardif

The difference in variances

sddif

The difference in standard deviations

ei1

the error index for original predicted distribution (see details)

ei1

the error index for scaled predicted distribution (see details)

Details

The comparison is done for mean, variance and standard deviation and shape. The shape is compared by computing the sum of absolute differences (error index) in densities for the observed data and predicted density in diameter classes specified by "limits". The error index has therefore a value between 0 (complete match) and 2 (complete mismatch). The error index is computed for the predicted density as such (ei1) and to a rescaled and switched density, which has exactly same mean and variance as the given diameter data (e12).

The error index is calculated as the sum of variable \((f_{obs}-f_{pred})x^{power}\) over the diameter classes, where \(x\) is the midpoint of the diaemeter class and \(f_{obs}-f_{pred}\) is the difference in predicted and observed frequency. By default, \(power=0\).

Examples

# NOT RUN {
# Example 
# Observed diameters 
d<-c(18.8,24.2,18.7,13.0,18.9,22.4,17.6,22.0,18.8,22.9,
     16.7,13.7,20.6,15.1,31.8,17.2,19.6,16.8,19.3,27.4,
	 23.7,18.2,19.7,18.9,23.0,21.4,23.8,22.1,24.2,20.9)

# Weibull(5,20) distribution in 1 cm classes (class limits from 0,...,60)
f<-pweibull(1:60,5,20)-pweibull(0:59,5,20)

# compare using the classified true distribution (approximate)
ddcomp(d,density=f,limitsd=0:60,limits=0:100,plot=TRUE)

# compare b specifying a Weibull dsitribution (accurate)
ddcomp(d,density="dweibull",shape=5,scale=20,plot=TRUE)
# }