R Under development (unstable) (2023-10-23 r85401 ucrt) -- "Unsuffered Consequences"
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> # Extended Rosenbrock Function ex_rosen.R from 
> # https://github.com/jlmelville/funconstrain by jlmelville
> # Test function 21 from the More', Garbow and Hillstrom paper.
> #
> # The objective function is the sum of \code{m} functions, each of \code{n}
> # parameters.
> #
> xrosn.f = function(par) {
+       n <- length(par)
+       if (n %% 2 != 0) {
+         stop("Extended Rosenbrock: n must be even")
+       }
+ 
+       fsum <- 0
+       for (i in 1:(n / 2)) {
+         p2 <- 2 * i
+         p1 <- p2 - 1
+ 
+         f_p1 <- 10 * (par[p2] - par[p1] ^ 2)
+         f_p2 <- 1 - par[p1]
+         fsum <- fsum + f_p1 * f_p1 + f_p2 * f_p2
+       }
+ 
+       fsum
+ }
> 
> xrosn.g = function(par) {
+       n <- length(par)
+       if (n %% 2 != 0) {
+         stop("Extended Rosenbrock: n must be even")
+       }
+ 
+       grad <- rep(0, n)
+       for (i in 1:(n / 2)) {
+         p2 <- 2 * i
+         p1 <- p2 - 1
+         xx <- par[p1] * par[p1]
+ 
+         yx <- par[p2] - xx
+         f_p1 <- 10 * yx
+         f_p2 <- 1 - par[p1]
+ 
+         grad[p1] <- grad[p1] - 400 * par[p1] * yx - 2 * f_p2
+         grad[p2] <- grad[p2] + 200 * yx
+       }
+ 
+       grad
+ }
> 
> 
> proc.time()
   user  system elapsed 
   0.12    0.03    0.14