R Under development (unstable) (2026-02-09 r89390 ucrt) -- "Unsuffered Consequences"
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> 
>  objfun <- function(x) {
+      stopifnot(is.numeric(x))
+      stopifnot(length(x) == 2)
+      f <- expression(x1^2 - x2^2)
+      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)
> 
>  options(digits = 3)
> 
>  goo <- trust(objfun, c(3, 1), 1, 5, blather = TRUE, iterlim = 20)
>  goo$converged
[1] FALSE
>  length(goo$r)
[1] 20
>  data.frame(type = goo$steptype, rho = goo$rho, change = goo$preddiff,
+      accept = goo$accept, r = goo$r)
        type rho  change accept r
1  easy-easy   1   -5.72   TRUE 1
2  easy-easy   1  -12.04   TRUE 2
3  easy-easy   1  -44.18   TRUE 4
4  easy-easy   1  -99.28   TRUE 5
5  easy-easy   1 -149.06   TRUE 5
6  easy-easy   1 -198.99   TRUE 5
7  easy-easy   1 -248.96   TRUE 5
8  easy-easy   1 -298.94   TRUE 5
9  easy-easy   1 -348.93   TRUE 5
10 easy-easy   1 -398.93   TRUE 5
11 easy-easy   1 -448.93   TRUE 5
12 easy-easy   1 -498.92   TRUE 5
13 easy-easy   1 -548.92   TRUE 5
14 easy-easy   1 -598.92   TRUE 5
15 easy-easy   1 -648.92   TRUE 5
16 easy-easy   1 -698.92   TRUE 5
17 easy-easy   1 -748.92   TRUE 5
18 easy-easy   1 -798.92   TRUE 5
19 easy-easy   1 -848.92   TRUE 5
20 easy-easy   1 -898.92   TRUE 5
> 
>  ##### note: FAILS to converge because function is unbounded -- optimum
>  #####     value does not exist
> 
>  (goo$stepnorm / goo$r)[goo$accept & goo$steptype != "Newton"]
 [1] 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
> 
> 
> proc.time()
   user  system elapsed 
   0.12    0.06    0.18