rxFun(name, args, cCode)

rxRmFun(name)

## Right now RxODE is not aware of the function f
## Therefore it cannot translate it to symengine or
## Compile a model with it.

try(RxODE("a=fun(a,b,c)"))

## Note for this approach to work, it cannot interfere with C
## function names or reserved RxODE specical terms.  Therefore
## f(x) would not work since f is an alias for bioaviability.

fun <- "
double fun(double a, double b, double c) {
  return a*a+b*a+c;
}
" ## C-code for function

rxFun("fun",c("a","b","c"), fun) ## Added function

## Now RxODE knows how to translate this function to symengine

rxToSE("fun(a,b,c)")

## And will take a central difference when calculating derivatives

rxFromSE("Derivative(fun(a,b,c),a)")

## Of course, you could specify the derivative table manually
rxD("fun", list(function(a,b,c){
  paste0("2*",a,"+",b);
},
    function(a,b,c){
     return(a)
    },
    function(a,b,c){
      return("0.0")
} ))

rxFromSE("Derivative(fun(a,b,c),a)")

# You can also remove the functions by `rxRmFun`

rxRmFun("fun")