R Under development (unstable) (2026-02-09 r89390 ucrt) -- "Unsuffered Consequences"
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> 
>  objfun <- function(x) {
+      ##### Rosenbrock's function #####
+      stopifnot(is.numeric(x))
+      stopifnot(length(x) == 2)
+      f <- expression(100 * (x2 - x1^2)^2 + (1 - x1)^2)
+      g1 <- D(f, "x1")
+      g2 <- D(f, "x2")
+      h11 <- D(g1, "x1")
+      h12 <- D(g1, "x2")
+      h22 <- D(g2, "x2")
+      x1 <- x[1]
+      x2 <- x[2]
+      f <- eval(f)
+      g <- c(eval(g1), eval(g2))
+      B <- rbind(c(eval(h11), eval(h12)), c(eval(h12), eval(h22)))
+      list(value = f, gradient = g, hessian = B)
+  }
> 
>  library(trust)
> 
>  parinit <- c(3, 1)
> 
>  out <- trust(objfun, parinit, 1, 1e5, blather = TRUE)
>  out$converged
[1] TRUE
>  length(out$r)
[1] 21
> 
>  parscale <- c(5, 1)
>  shift <- 4
>  theta <- parscale * (parinit + shift)
> 
>  pobjfun <- function(x) {
+      out <- objfun(x / parscale - shift)
+      out$gradient <- out$gradient / parscale
+      out$hessian <- out$hessian / outer(parscale, parscale)
+      return(out)
+  }
> 
>  pout <- trust(pobjfun, theta, 1, 1e5, blather = TRUE)
>  pout$converged
[1] TRUE
>  length(pout$r)
[1] 25
>  all.equal(out$argument, pout$argument / parscale - shift)
[1] "Mean relative difference: 1.011409e-07"
> 
>  qout <- trust(objfun, parinit, 1, 1e5, parscale = parscale, blather = TRUE)
>  qout$converged
[1] TRUE
>  length(qout$r)
[1] 25
> 
>  all.equal(pout$valpath, qout$valpath)
[1] TRUE
>  transpath <- pout$argpath
>  transpath <- sweep(transpath, 2, parscale, "/")
>  transpath <- sweep(transpath, 2, shift)
>  all.equal(transpath, qout$argpath)
[1] TRUE
> 
> 
> proc.time()
   user  system elapsed 
   0.18    0.06    0.20