用deSolve解决ODE的R-导数错误

Question

I am trying to use the deSolve package for a set of ODE's with equations as auxiliary variables. I keep getting the error where the number of derivatives isn't the same length as the initial conditions vector. What should I change?

# rm(list=ls())  
library(deSolve)

exponential=function(t,state,parameters){ with(as.list( c(state,parameters)), {

   #Aux. Var.
   fX2 = pmax(0,1-(1-(d2/r12)*(X2/K2)))
   fX1 = X1/(X1+k1); 

   # equations (ODE)
   dX1 = C-((d1)*(X1))-(r12)*(X2)*fX2*fX1 # differential equaion
   dX2 = r12*(X2)*fX2*fX1-((d2)*(X2))

   return(list(c(dX1, dX2)))
   })
 }

# -- RUN INFORMATION

# Set Initial Values and Simulation Time
state = c(X1=2,X2=0.01,K2= 10)
times=0:100

# Assign Parameter Values
parameters = c(d1=0.001, d2=0.008, r12=0.3,C=0.5,k1= 0.001)

for (i in 1:length(times)){
  out= ode(y=state,times=times,func=exponential,parms=parameters)
  }

Error in checkFunc(Func2, times, y, rho) : 
  The number of derivatives returned by func() (2) must equal the length of
 the initial conditions vector (3)**

Answer 1

The error comes from the return in your defined function: Your input parameter y has length 3, but you only return 2 values back, that's the error. You can solve your problem with

return(list(c(X1, X2, K2)))

Another possibility is to take K2 to the parameters, then your old return was right. You have to decide if K2 is a variable or a parameter.

And BTW: Why a for loop with the time? In my opinion that is not necessary, because the ODEs are solved in the timeinterval you submitted to the ode function.

out= ode(y=state,times=times,func=exponential,parms=parameters)