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).

## Usage

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

## Arguments

- 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`

.

## Value

An updated `problem()`

object 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/cplex-optimizer>).

## Installation

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:

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:

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

## References

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

## See also

Other solvers:
`add_cbc_solver()`

,
`add_default_solver()`

,
`add_gurobi_solver()`

,
`add_highs_solver()`

,
`add_lsymphony_solver`

,
`add_rsymphony_solver()`

## Examples

```
# \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)
# }
```