I use:

platform i386-pc-mingw32

arch x86

os Win32

system x86, Win32

status

major 1

minor 4.1

year 2002

month 01

day 30

language R

I try to fit a 2 compartment model. The compartments are open, connected

to each other and are filled via constant input and a time depended

function as well. Data describes increasing of Apo B after dialysis. Aim

of the analysis is to test the hypothesis whether the data could described

by two simple disconnected one compartment modes ore the "saturated

model" holds? The first order differential equation for the saturated

model:

db5 = - (k50+k56)*b5 + k56*b6 + c*g(t) + h

db6 = + k65*b5 - (k60+k65)*b6 + d

db5, db6 are the first derivatives, b5, b6 are the functions to be

fitted. The remaining parameters are unknown and should follow from the

fit.

assuming that g(t) has the functional form: b4i + (b40-b4i)*exp(-k4*t)

(after calculations of 2 papers of A4) follows the solution:

L5L6 <- function(b40, b4i, k4, t, p50, p56, p60, p65, pc, ph, pd, pb50,

pb60) {

k50 <- exp(p50)

k56 <- exp(p56)

k60 <- exp(p60)

k65 <- exp(p65)

c <- exp(pc)

h <- exp(ph)

d <- exp(pd)

b50 <- exp(pb50)

b60 <- exp(pb60)

a <- (k50+k56)

b <- k65

e <- k56

f <- (k60+k65)

z1 <- (-(a+f)/2 - sqrt((a+f)^2/4 - a*f + b*e))

z2 <- (-(a+f)/2 + sqrt((a+f)^2/4 - a*f + b*e))

K <- ((z1+a)/(z2-z1))

B1 <- (b/(z2-z1)*b60 - K*b50)

A1 <- (b50-B1)

X1 <- (b*d/(z2-z1)-K*(c*b4i+h))

X2 <- (K*c*(b4i-b40))

X3 <- (c*b4i + h - X1)

X4 <- (c*(b40-b4i)- X2)

C1E <- (X3/(-z1)*(1-exp(z1*t)) +

X4/(-(k4+z1))*(exp(-k4*t)-exp(z1*t)))

C2E <- (X1/(-z2)*(1-exp(z2*t)) +

X2/(-(k4+z2))*(exp(-k4*t)-exp(z2*t)))

b5 <- (A1*exp(z1*t) + B1*exp(z2*t) + C1E + C2E)

b6 <- ((z1+a)/b * A1*exp(z1*t) + (z2+a)/b * B1*exp(z2*t) +

(z1+a)/b * C1E + (z2+a)/b * C2E)

y <- f5*b5 + f6*b6

return(y)

}

I am in the lucky circumstances having starting values, because a nlr-fit

succeeds, the graphical presentation of the fits looks quite nice. The nlr

function is part of Lindsey's library(gnlm), but now I would like to apply

Pinheiro and Bates library(nlme) and I have got an error:

m2 <- nls(y ~ L5L6(b40, b4i, k4, t, p50, p56, p60, p65, pc, ph, pd,

pb50, pb60),

+ data=help, start=c(p50=0.008678954, p56=-0.595153967,

+ p60=-4.602990518, p65=-0.625732096,

+ pc=-0.128657978, ph=0.708033556, pd=1.140357461, pb50=1.311141424,

+ pb60=1.270852258))

Error in numericDeriv(form[[3]], names(ind), env) :

Missing value or an Infinity produced when evaluating the model

If somebody feel that he can help me, I could send him my R- code andpb50, pb60),

+ data=help, start=c(p50=0.008678954, p56=-0.595153967,

+ p60=-4.602990518, p65=-0.625732096,

+ pc=-0.128657978, ph=0.708033556, pd=1.140357461, pb50=1.311141424,

+ pb60=1.270852258))

Error in numericDeriv(form[[3]], names(ind), env) :

Missing value or an Infinity produced when evaluating the model

data file as well.

Kind regards,

Dominik

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