add_rsymphony_solver: Add a SYMPHONY solver with Rsymphony

Description

Specify that the SYMPHONY software should be used to solve a conservation planning problem using the Rsymphony package. This function can also be used to customize the behavior of the solver. It requires the Rsymphony package.

Usage

add_rsymphony_solver(x, gap = 0.1, time_limit = -1,
  first_feasible = 0, verbose = TRUE)

Arguments

ConservationProblem-class object.

gap

numeric gap to optimality. This gap is absolute and expresses the acceptable deviance from the optimal objective. For example, solving a minimum set objective problem with a gap of 5 will cause the solver to terminate when the cost of the solution is within 5 cost units from the optimal solution.

time_limit

numeric time limit in seconds to run the optimizer. The solver will return the current best solution when this time limit is exceeded.

first_feasible

logical should the first feasible solution be be returned? If first_feasible is set to TRUE, the solver will return the first solution it encounters that meets all the constraints, regardless of solution quality. Note that the first feasible solution is not an arbitrary solution, rather it is derived from the relaxed solution, and is therefore often reasonably close to optimality.

verbose

logical should information be printed while solving optimization problems? Defaults to TRUE.

Value

ConservationProblem-class object with the solver added to it.

Details

SYMPHONY is an open-source integer programming solver that is part of the Computational Infrastructure for Operations Research (COIN-OR) project, an initiative to promote development of open-source tools for operations research (a field that includes linear programming). The Rsymphony package provides an interface to COIN-OR and is available on CRAN. This solver uses the Rsymphony package to solve problems.

Examples

Run this code

# NOT RUN {
# load data
data(sim_pu_raster, sim_features)

# create problem
p <- problem(sim_pu_raster, sim_features) %>%
  add_min_set_objective() %>%
  add_relative_targets(0.1) %>%
  add_binary_decisions()
# }
# NOT RUN {
# if the package is installed then add solver and generate solution
if (require("Rsymphony")) {
  # specify solver and generate solution
  s <- p %>% add_rsymphony_solver(time_limit = 10) %>%
             solve()

  # plot solutions
  plot(stack(sim_pu_raster, s), main = c("planning units", "solution"),
       axes = FALSE, box = FALSE)
}
# }
# NOT RUN {
# }