R/add_default_solver.R

In oppr: Optimal Project Prioritization

#' @include Solver-proto.R
NULL

#' Add a default solver
#'
#' Identify the best solver currently installed on the system and specify that
#' it should be used to solve a project prioritization [problem()].
#'
#' @param x [ProjectProblem-class] object.
#'
#' @param ... arguments passed to the solver.
#'
#' @details
#'   Ranked from best to worst, the solvers that can be used are:
#'   \pkg{gurobi}, ([add_gurobi_solver()]),
#'   \pkg{Rsymphony} ([add_rsymphony_solver()]), \pkg{lpsymphony}
#'   ([add_lpsymphony_solver()]), and \pkg{lpSolveAPI}
#'   ([add_lpsolveapi_solver()]). This function does not consider
#'   solvers that generate solutions using heuristic algorithms (i.e.
#'   [add_heuristic_solver()]) or random processes
#'   (i.e. [add_random_solver()]) because they cannot provide
#'   any guarantees on solution quality.
#'
#' @seealso [solvers].
#'
#' @examples
#' # load data
#' data(sim_projects, sim_features, sim_actions)
#'
#' # build problem with default solver
#' p <- problem(sim_projects, sim_actions, sim_features,
#'              "name", "success", "name", "cost", "name") %>%
#'      add_max_richness_objective(budget = 200) %>%
#'      add_binary_decisions() %>%
#'      add_default_solver()
#'
#' # print problem
#' print(p)
#'
#' \dontrun{
#' # solve problem
#' s <- solve(p)
#'
#' # print solution
#' print(s)
#'
#' # plot solution
#' plot(p, s)
#' }
#' @export
add_default_solver <- function(x, ...) {
  ds <- default_solver_name()
  if (identical(ds, "gurobi")) {
    return(add_gurobi_solver(x, ...))
  } else if (identical(ds, "Rsymphony")) {
    return(add_rsymphony_solver(x, ...))
  } else if (identical(ds, "lpsymphony")) {
    return(add_lpsymphony_solver(x, ...))
  } else if (identical(ds, "lpSolveAPI")) {
    return(add_lpsolveapi_solver(x, ...))
  } else {
    assertthat::assert_that(inherits(x, "ConservationProblem"))
    return(x$add_solver(pproto(
      "MissingSolver",
      Solver,
      name = "MissingSolver",
      solve = function(self, x) {
        stop("no optimization problem solvers found on system.")
      })))
  }
}

#' Default solver name
#'
#' This function returns the name of the default solver. If no solvers are
#' detected on the system, then a `NULL` object is returned.
#'
#' @details This function tests if any of the following packages are installed:
#'   \pkg{Rsymphony}, \pkg{lpsymphony}, \pkg{gurobi}, \pkg{lpSolveAPI}.
#'
#' @return `character` indicating the name of the default solver.
#'
#' @noRd
default_solver_name <- function() {
  if (requireNamespace("gurobi", quietly = TRUE)) {
    return("gurobi")
  } else if (requireNamespace("Rsymphony", quietly = TRUE)) {
    return("Rsymphony")
  } else if (requireNamespace("lpsymphony", quietly = TRUE)) {
    return("lpsymphony")
  } else {
    return("lpSolveAPI")
  }
}