Hi, Try with the following ODE function. This should give you an extra column with the derivative of G in your THAAC matrix.
degradation = function (t, state, parameters) { with(as.list(c(state, parameters)), {dG = (-a*(t+i)^b)*(G) list(c(dG),dG=dG) }) } Any additional variables that you want to output from your ODE system function need to be a separate level of the output list. For instance: # Example taken from the deSolve vignette parameters <- c(a = -8/3,b = -10, c = 28) state <- c(X = 1,Y = 1, Z = 1) Lorenz<-function(t, state, parameters) { with(as.list(c(state, parameters)),{ # rate of change dX <- a*X + Y*Z dY <- b * (Y-Z) dZ <- -X*Y + c*Y - Z # return the rate of change list(c(dX, dY, dZ),dX=dX, dY=dY,Dummy=-X/Y) }) # end with(as.list ... } times <- seq(0, 100, by = 0.01) library(deSolve) out <- ode(y = state, times = times, func = Lorenz, parms = parameters) head(out) Sebastien ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.