Displaying 6 results from an estimated 6 matches for "nrhyperbola".
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hyperbola
2005 Oct 26
1
help with a self-starting function in nonlinear least squares regression.
Hello. I am having a problem setting up a self-starting function for
use in nonlinear regression (and eventually in the mixed model version).
The function is a non-rectangular hyperbola - called "NRhyperbola" -
which is used for fitting leaf photosynthetic rate to light intensity.
It has one independent variable (Irr) and four parameters (theta, Am,
alpha and Rd). I have created this to act as a self-starting function.
The self-starting function seems to work (i.e. when I call "getInitial&qu...
2005 Oct 26
0
self starting function for nonlinear least squares.
Following on my posting of this morning, concerning a problem that I am
having constructing a self-starting function for use with nls (and
eventually with nlsList and nlme), the following is the self-starting
function called NRhyperbola:
> NRhyperbola
function (Irr,theta,Am,alpha,Rd)
{
# Am is the maximum gross photosynthetic rate
# Rd is the dark resiration rate (positive value)
# theta is the shape parameter
# alpha is the initial quantum yeild
#
(1/(2*theta))*
(alpha*Irr + Am - sqrt((alpha*Irr + Am)^2 -4*alpha*...
2005 Nov 09
0
source of "susbcript out of bounds error" in nmle
..., pages 342-347) describe how to construct a
self-starting function for use in nls, nlsList and nlme. A
self-starting function provides, not only the function to be evaluated,
but also estimates of initial values of the parameters that are to be
estimated. I have written a self-starting function (NRhyperbola) for a
non-rectangular hyperbola with 4 parameters (theta, Am, alpha, Rd). The
function works:
>
getInitial(Photosynthese~NRhyperbola(Irr,theta,Am,alpha,Rd),data=lit.dat
a2,na.action=na.omit)
theta Am alpha Rd
0.69495045 35.32201003 0.03156335 1.26873011...
2005 Oct 27
1
syntax of nlme with nesting
...e case. I have mastered the lme function but the
nlme function has me stumped.
I am attempting to fit a nonlinear mixed model with 4 levels of nesting.
I am getting a cryptic error message and do not know what is wrong with
the syntax of the call. This is the call:
> nlme(Photosynthese~NRhyperbola(Irr,theta,Am,alpha,Rd),
+ fixed=theta+Am+alpha+Rd~1,
+ random=theta~1|Reference/Espece/Plante/Groupe,
+ data=lit.data)
NRhyperbola is a self-starting function with one variable (Irr) and four
parameters (theta,Am,alpha,Rd). The data set (lit.data) contains
Photosynthese (dependent variable)...
2005 Sep 01
1
making self-starting function for nls
...s, I am trying to
write a self-starting nonlinear function (a non-rectagular hyperbola) to
be used in nonlinear least squares regression (and eventually for a
mixed model). When I use the getInitial function for my self-starting
function I get the following error message:
> getInitial(photo~NRhyperbola(Irr,theta,Am,alpha,Rd),dat)
Error in tapply(y, x, mean, na.rm = TRUE) :
arguments must have same length
Since I do not explicitly call tapply in my function that makes
NRhyperbola a self-starting function (called NRhyperbolaInit, see
below), I assume that the error is coming from wit...
2005 Nov 09
1
strategies to obtain convergence using nlme
...convergence using
nlme.
My function is a non-rectangular hyperbola with 4 parameters (theta, Am,
alpha, Rd):
#Nonrectangular hyperbola for photosynthesis
# myfunct
(1/(2*theta))*(
alpha*Irr + Am -sqrt((alpha*Irr+Am)^2-4*alpha*theta*Am*Irr))-Rd
I have written a self-starting function (NRhyperbola) to provide
starting values. This self-starting function works. When I use this
self-starting function with nlsList using a data set with the grouping
variable (and after removing a few groups for which there is an
insufficient range of the independent variable to provide estimates), I
get converg...