Specify that the
*IBM CPLEX* software
should be used to solve a conservation planning problem (IBM 2017) .
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
)
```

- x
`problem()`

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`

.

An updated `problem()`

object with the solver added to it.

*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/cplex-optimizer>).

The cplexAPI package is used to interface with *IBM CPLEX* software.
To install the package, the *IBM CPLEX* software must be installed
(see https://www.ibm.com/products/ilog-cplex-optimization-studio/cplex-optimizer). Next, the `CPLEX_BIN`

environmental variable must be set to specify the file path for the
*IBM CPLEX* software. For example, on a Linux system,
this variable can be specified by adding the following text to the
`~/.bashrc`

file:

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

Please Note that you may need to change the version number in the file path
(i.e., `"CPLEX_Studio128"`

). After specifying the `CPLEX_BIN`

environmental variable, the cplexAPI package can be installed.
Since the cplexAPI package is not available on the
the Comprehensive R Archive Network (CRAN), it must be installed from
its GitHub repository. To
install the cplexAPI package, please use the following code:

```
if (!require(remotes)) install.packages("remotes")
::install_github("cran/cplexAPI") remotes
```

For further details on installing this package, please consult the installation instructions.

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

Other solvers:
`add_cbc_solver()`

,
`add_default_solver()`

,
`add_gurobi_solver()`

,
`add_highs_solver()`

,
`add_lsymphony_solver`

,
`add_rsymphony_solver()`

```
# \dontrun{
# load data
sim_pu_raster <- get_sim_pu_raster()
sim_features <- get_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)
# }
```