```
## Rosenbrock function: The flat valley of the Rosenbruck function makes
## it infeasible for a steepest descent approach.
# rosenbrock <- function(x) {
# n <- length(x)
# x1 <- x[2:n]
# x2 <- x[1:(n-1)]
# sum(100*(x1-x2^2)^2 + (1-x2)^2)
# }
# steep_descent(c(1, 1), rosenbrock)
# Warning message:
# In steep_descent(c(0, 0), rosenbrock) :
# Maximum number of iterations reached -- not converged.
## Sphere function
sph <- function(x) sum(x^2)
steep_descent(rep(1, 10), sph)
# $xmin 0 0 0 0 0 0 0 0 0 0
# $fmin 0
# $niter 2
```

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