I want to get the derivative value from the function below when x = 2. Is there way to keep the form of the function and also get derivative value with out any additional package?
f <- function(x)
return(x^3)
For example, I have tried below but they didn't work.
x=2
deriv(~f, "x")
x=2
deriv(~body(f),"x")
x=2
D(expression(f),"x")
You can use deriv, however, one caveat is that you can only use expressions/calls.
derivative = deriv(~ x^3, "x")
x <- 2
eval(derivative )
With a named expression:
f = expression(x^3)
dx2x <- D(f,"x")
and the rest is the same.
See this link for the documentation: https://www.rdocumentation.org/packages/Deriv/versions/3.8.2/topics/Deriv
This would be approximation
foo = function(x, delta = 1e-5, n = 3){
x = seq(from = x - delta, to = x + delta, length.out = max(2, n))
y = x^3
mean(diff(y)/diff(x))
}
foo(2)
#[1] 12