fitbusscher: Self-starting Nls Busscher's (1990) Model for Soil...

In soilphysics: Soil Physical Analysis

Description

Function to self start the nonlinear Busscher's (1990) model for penetration resistance, i.e., Pr = b0 * (θ ^ {b1}) * (Bd ^ {b2}). It creates initial estimates (by log-linearization) of the parameters b0, b1 and b2 and uses them to provide its least-squares estimates through nls.

Usage

 fitbusscher(Pr, theta, Bd, ...) 

Arguments

Pr	a numeric vector containing penetration resistance values.
theta	a numeric vector containing soil moisture values at which to evaluate the model.
Bd	a numeric vector containing bulk density values at which to evaluate the model.
...	further arguments to nls.

Value

A nls output (see help(nls)).

Author(s)

Anderson Rodrigo da Silva <[e-mail]>

References

Busscher, W. J. (1990). Adjustment of flat-tipped penetrometer resistance data to common water content. Transactions of the ASAE, 3:519-524.

See Also

fitlbc, nls, summary.nls, predict.nls, Rsq

Examples

data(compaction)
attach(compaction)
out <- fitbusscher(Pr = PR, theta = Mois, Bd = BD)
summary(out)
Rsq(out)

# 3D plot
X <- seq(min(Mois), max(Mois), len = 30) # theta
Y <- seq(min(BD), max(BD), len = 30) # Bd
f <- function(x, y) coef(out)[1] * (x^coef(out)[2]) * (y^coef(out)[3])
Z <- outer(X, Y, f)
persp(X, Y, Z,
	xlab = "Soil moisture",
	ylab = "Soil bulk density",
	zlab = "Penetration resistance",
	ticktype = "detailed",
	phi = 20, theta = 30)

# End (not run)

Example output

Loading required package: rpanel
Loading required package: tcltk
Package `rpanel', version 1.1-4: type help(rpanel) for summary information
Loading required package: MASS
Loading required package: tkrplot
---
soilphysics version 3.1

Warning messages:
1: no DISPLAY variable so Tk is not available 
2: loading Rplot failed 

Formula: Pr ~ b0 * (theta^b1) * (Bd^b2)

Parameters:
   Estimate Std. Error t value Pr(>|t|)    
b0   1.1680     0.2618   4.461 5.07e-05 ***
b1  -0.8770     0.2247  -3.903 0.000302 ***
b2   0.1105     0.5399   0.205 0.838741    
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Residual standard error: 0.5579 on 47 degrees of freedom

Number of iterations to convergence: 6 
Achieved convergence tolerance: 2.675e-06

$pseudo.R.squared
[1] 0.8961571

$adj.R.squared
[1] 0.8917383

attr(,"class")
[1] "Rsq"

soilphysics documentation built on Jan. 13, 2021, 7:06 p.m.