Hello,

I have to do a research project for my Systems Biology class and I am finding many difficulties in coding the system of ODEs that I have generated as I am really unexperienced in R.

Here is my code. When I compute it I get an

Error in eval(substitute(expr), data, enclos = parent.frame()) :

object 'rTr' not found

```
MergeModel <- function(Time, State, Pars) {
with(as.list(c(State, Pars)), {
# ------------------------------------------------
# Treg equation (number 8)
# ------------------------------------------------
deathRate <- rTr*Tr
productionRate <- lambdaTrI2*Tb*(I2/(KI2+I2))*(M/(M+KM))*(KTa/(Ta+KTa))
GCRate <- a*(1-e^(-g))*Tr
dTrdt <- productionRate + GCRate - deathRate
return(list(c(dTrdt)))
# ------------------------------------------------
})
}
Pars <- c(rTr = 1.97*10^(-1),
lambdaTrI2 = 1.76*10^8,
Tb = 1.55*10^(-7),
KI2 = 5*10^(-7),
I2 = 5.2*10^(-7),
M = 10^(-3),
KM = 3*10^(-3),
KTa = 5*10^(-7),
Ta = 1.56*10^(-7),
a = 1.0483,
g = 1 )
y0 <- c(Tr = 5.372*10^(-3))
timespan <- seq(0, 100, by = 1)
MergeModel.sol <- ode(y0, timespan, MergeModel, pars)
summary(MergeModel.sol)
```

I do not understand why the Pars function seems to not be working... My report is due tonight so if somebody could help me out I would greatly appreciate it.

For some background, I am modeling a glucocorticoid treatment of sarcoidosis disease (called Merge Model), the equation presented here corresponds to the effect of this drug in a specific cell population called Treg (Tr).

Thank you very much!