search for: photosynthet

Displaying 3 results from an estimated 3 matches for "photosynthet".

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2004 Apr 01
1
nls function
Hello. I am trying to fit a non-rectangular hyperbola function to data of photosynthetic rate vs. light intensity. There are 4 parameters that have to be estimated. I find the nls function very difficult to use because it often fails to converge and then gives out cryptic error messages. I have tried playing with the control parameters but this does not always help. Is there anot...
2005 Oct 26
0
self starting function for nonlinear least squares.
...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*theta*Am*Irr))- Rd } attr(,"initial") function (mCall, LHS, data) { xy <- sor...
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" it provides the initial values), but I can't...