方便的方法来找到r中函数的导数？

Question

有没有一种方便的方法可以在r中找到（正常密度）函数的导数？

Answer 1

是的，有。请参阅help("D")。

DD <- function(expr, name, order = 1) {
  if(order < 1) stop("'order' must be >= 1")
  if(order == 1) D(expr, name)
  else DD(D(expr, name), name, order - 1)
}

ddnorm <- function(x) eval(DD(expression(dnorm(x)), "x", order = 1))
dddnorm <- function(x) eval(DD(expression(dnorm(x)), "x", order = 2))

curve(dnorm(x), -2, 2, ylim = c(-0.4, 0.4))
curve(ddnorm(x), -2, 2, add = TRUE, col = "dark red")
curve(dddnorm(x), -2, 2, add = TRUE, col = "dark blue")

legend(x = "topleft", legend = c("dnorm", "first derivative", "second derivative"),
       col = c("black", "dark red", "dark blue"),
       lty = 1)