Add a CPLEX solver

Specify that the IBM CPLEX software (IBM 2017) should be used to solve a conservation planning problem(). This function can also be used to customize the behavior of the solver. It requires the cplexAPI package to be installed (see below for installation instructions).

add_cplex_solver(
  x,
  gap = 0.1,
  time_limit = .Machine$integer.max,
  presolve = TRUE,
  threads = 1,
  verbose = TRUE
)

Arguments

x: problem() (i.e., ConservationProblem) object.
gap: numeric gap to optimality. This gap is relative and expresses the acceptable deviance from the optimal objective. For example, a value of 0.01 will result in the solver stopping when it has found a solution within 1% of optimality. Additionally, a value of 0 will result in the solver stopping when it has found an optimal solution. The default value is 0.1 (i.e., 10% from optimality).
time_limit: numeric time limit (seconds) for generating solutions. The solver will return the current best solution when this time limit is exceeded. The default value is the largest integer value (i.e., .Machine$integer.max), effectively meaning that solver will keep running until a solution within the optimality gap is found.
presolve: logical attempt to simplify the problem before solving it? Defaults to TRUE.
threads: integer number of threads to use for the optimization algorithm. The default value is 1.
verbose: logical should information be printed while solving optimization problems? Defaults to TRUE.

Value

Object (i.e., ConservationProblem) with the solver added to it.

Details

IBM CPLEX is a commercial optimization software. It is faster than the available open source solvers (e.g., add_lpsymphony_solver() and add_rsymphony_solver(). Although formal benchmarks examining the performance of this solver for conservation planning problems have yet to be completed, preliminary analyses suggest that it performs slightly slower than the Gurobi solver (i.e., add_gurobi_solver()). We recommend using this solver if the Gurobi solver is not available. Licenses are available for the IBM CPLEX software to academics at no cost (see https://www.ibm.com/products/ilog-cplex-optimization-studio).

Installation

The pkgcplexAPI package is used to interface with IBM CPLEX. To install this package, the CPLEX_BIN variable must be set (similar to the GUROBI_HOME variable for the Gurobi software) to specify the file path for the CPLEX software. For example, on a Linux system, this variable can be specified by adding the following text to the ~/.bashrc file:

  export CPLEX_BIN="/opt/ibm/ILOG/CPLEX_Studio128/cplex/bin/x86-64_linux/cplex"

Note that you may need to change the version number in the file path (i.e., "CPLEX_Studio128"). For more information on installing the pkgcplexAPI package, please see the official installation instructions for the package.

References

IBM (2017) IBM ILOG CPLEX Optimization Studio CPLEX User's Manual. Version 12 Release 8. IBM ILOG CPLEX Division, Incline Village, NV.

Examples

# \dontrun{
# 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() %>%
     add_cplex_solver(gap = 0.1, time_limit = 5, verbose = FALSE)

# generate solution
s <- solve(p)

# plot solution
plot(s, main = "solution", axes = FALSE, box = FALSE)

# }