context("testing psqn-bfgs")

test_that("we get the right result with the Rosenbrock Banana function", {
  fn <- function(x) {
    x1 <- x[1]
    x2 <- x[2]
    100 * (x2 - x1 * x1)^2 + (1 - x1)^2
  }
  gr_psqn <- function(x) {
    x1 <- x[1]
    x2 <- x[2]
    out <- c(-400 * x1 * (x2 - x1 * x1) - 2 * (1 - x1),
             200 *      (x2 - x1 * x1))
    attr(out, "value") <- 100 * (x2 - x1 * x1)^2 + (1 - x1)^2
    out
  }

  res <- psqn_bfgs(c(-1.2, 1), fn, gr_psqn)
  expect_equal(res$par, c(1, 1))
  expect_equal(res$value, 0)
  expect_true(res$convergence)
  expect_equal(res$info, 0L)

  gr_tol <- 1e-8
  res <- psqn_bfgs(c(-1.2, 1), fn, gr_psqn, rel_eps = 1, gr_tol = gr_tol)
  expect_lt(sqrt(sum(gr_psqn(res$par)^2)), gr_tol)

  abs_eps <- 1e-2
  new_res <- psqn_bfgs(c(-1.2, 1), fn, gr_psqn, rel_eps = 1, abs_eps = abs_eps)
  # this is not guaranteed but it works in this case
  expect_lt(abs(new_res$value - res$value), abs_eps)
})