Rcpp call R optim (R code part)

library(Rcpp)
sourceCpp("optim_cpp.cpp")
fr <- function(x) {   ## Rosenbrock Banana function
  x1 <- x[1]
  x2 <- x[2]
  100 * (x2 - x1 * x1)^2 + (1 - x1)^2
}
grr <- function(x) { ## Gradient of 'fr'
  x1 <- x[1]
  x2 <- x[2]
  c(-400 * x1 * (x2 - x1 * x1) - 2 * (1 - x1),
    200 *      (x2 - x1 * x1))
}
optim_cpp(fr, grr, c(-1.2,1), method = "BFGS")

optim(c(-1.2,1), fr, grr, method = "BFGS")