#' @title
#' DTLZ1 Function (family)
#'
#' @description
#' Builds and returns the multi-objective DTLZ1 test problem.
#'
#' The DTLZ1 test problem is defined as follows:
#'
#' Minimize \eqn{f_1(\mathbf{x}) = \frac{1}{2} x_1 x_2 \cdots x_{M-1} (1+g(\mathbf{x}_M),}{
#' f[1](X) = 1/2 * x[1] * x[2] * ... * x[M-1] * (1 + g(XM))}
#'
#' Minimize \eqn{f_2(\mathbf{x}) = \frac{1}{2} x_1 x_2 \cdots (1-x_{M-1}) (1+g(\mathbf{x}_M)),}{
#' f[2](X) = 1/2 * x[1] * x[2] * ... * (1 - x[M-1]) * (1 + g(XM))}
#'
#' \eqn{\vdots\\}{...}
#'
#' Minimize \eqn{f_{M-1}(\mathbf{x}) = \frac{1}{2} x_1 (1-x_2) (1+g(\mathbf{x}_M)),}{
#' f[M-1](X) = 1/2 * x[1] * (1 - x[2]) * (1 + g(XM))}
#'
#' Minimize \eqn{f_{M}(\mathbf{x}) = \frac{1}{2} (1-x_1) (1+g(\mathbf{x}_M)),}{
#' f[M](X) = 1/2 * (1 - x[1]) * (1 + g(XM))}
#'
#' with \eqn{0 \leq x_i \leq 1}{0 <= x[i] <= 1}, for \eqn{i=1,2,\dots,n,}{i=1,2,...,n}
#'
#' where \eqn{g(\mathbf{x}_M) = 100 \left[|\mathbf{x}_M| + \sum\limits_{x_i \in \mathbf{x}_M} (x_i - 0.5)^2 - \cos(20\pi(x_i - 0.5))\right]}{
#' g(XM) = 100 * (|XM| + sum{x[i] in XM} {(x[i] - 0.5)^2 - cos(20 * pi * (x[i] - 0.5))})}
#'
#' @references K. Deb and L. Thiele and M. Laumanns and E. Zitzler. Scalable
#' Multi-Objective Optimization Test Problems. Computer Engineering and Networks
#' Laboratory (TIK), Swiss Federal Institute of Technology (ETH) Zurich, 112, 2001
#'
#' @param dimensions [\code{integer(1)}]\cr
#' Number of decision variables.
#' @param n.objectives [\code{integer(1)}]\cr
#' Number of objectives.
#' @return [\code{smoof_multi_objective_function}]
#' Returns an instance of the DTLZ1 family as a \code{smoof_multi_objective_function} object.
#' @export
makeDTLZ1Function = function(dimensions, n.objectives) {
checkmate::assertInt(n.objectives, lower = 2L)
checkmate::assertInt(dimensions, lower = n.objectives)
# Renaming vars here to stick to the notation in the paper
# number of decision variables in the last group (see x_m in the paper)
k = dimensions - n.objectives + 1
M = n.objectives
force(M)
force(k)
# C++ implementation
fn = function(x) {
checkNumericInput(x, dimensions)
dtlz_1(x, M)
}
# Reference R implementation
# fn = function(x) {
# assertNumeric(x, len = dimensions, any.missing = FALSE, all.missing = FALSE)
# f = numeric(M)
# n = length(x)
# xm = x[M:n]
# g = 100 * (k + sum((xm - 0.5)^2 - cos(20 * pi * (xm - 0.5))))
# a = 0.5 * (1 + g)
# prod.xi = 1
# for(i in M:2) {
# f[i] = a * prod.xi * (1 - x[M - i + 1])
# prod.xi = prod.xi * x[M - i + 1]
# }
# f[1] = a * prod.xi
# return(f)
# }
makeMultiObjectiveFunction(
name = "DTLZ1 Function",
id = paste0("dtlz1_", dimensions, "d_", n.objectives, "o"),
description = "Deb et al.",
fn = fn,
par.set = ParamHelpers::makeNumericParamSet(
len = dimensions,
id = "x",
#FIXME: any box constraints?
lower = rep(0, dimensions),
upper = rep(1, dimensions),
vector = TRUE
),
n.objectives = n.objectives,
ref.point = rep(11, n.objectives)
)
}
class(makeDTLZ1Function) = c("function", "smoof_generator")
attr(makeDTLZ1Function, "name") = c("DTLZ1")
attr(makeDTLZ1Function, "type") = c("multi-objective")
attr(makeDTLZ1Function, "tags") = c("multi-objective")
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