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Save the mathematical formulation for a conservation planning problem to a file for mixed integer programming solvers. Note that this function requires either the Rsymphony or gurobi package to be installed.

Usage

write_problem(x, path, solver = NULL)

Arguments

x

problem() object.

path

character file path to save the problem formulation. The argument should contain a ".lp" or .mps" file extension to specify whether the problem formulation will be saved in the LP or MPS format (respectively).

solver

character name of optimization solver to write the problem to disk. Available options include: "rsymphony" , "gurobi", or NULL. Note that using the Gurobi solver is much faster, because the Rsymphony solver requires attempting to solve the problem before it can be written. Defaults to NULL, such that the best available solver is used.

Value

An invisible TRUE indicating success.

Examples

# \dontrun{
# set seed for reproducibility
set.seed(500)

# load data
sim_pu_polygons <- get_sim_pu_polygons()
sim_features <- get_sim_features()

# subset data to extract first four planning units
sim_pu_polygons <- sim_pu_polygons[1:4, ]

# create minimal problem
p <-
  problem(sim_pu_polygons, sim_features, cost_column = "cost") %>%
  add_min_set_objective() %>%
  add_relative_targets(0.1) %>%
  add_binary_decisions()

# specify file path to save problem formulation
path <- file.path(tempdir(), "model.lp")
print(path)
#> [1] "/tmp/Rtmpo4hu7p/model.lp"

# save problem to file
## note that either the gurobi or Rsymphony package needs to be installed
write_problem(p, path)
#> Set parameter Username
#> Academic license - for non-commercial use only - expires 2025-04-21

# print model file
cat(readLines(path), sep = "\n")
#> \ Model R
#> \ LP format - for model browsing. Use MPS format to capture full model detail.
#> Minimize
#>   215.8638399028077 C0 + 212.7823480801063 C1 + 207.4962437102063 C2
#>    + 208.9321699486367 C3
#> Subject To
#>  R0: 0.7150548100471497 C0 + 0.6990428566932678 C1 + 0.6859316825866699 C2
#>    + 0.6783192753791809 C3 >= 0.2778348624706268
#>  R1: 0.2900900840759277 C0 + 0.3052216172218323 C1 + 0.3266035616397858 C2
#>    + 0.3510976731777191 C3 >= 0.1273012936115265
#>  R2: 0.8178213238716125 C0 + 0.8064534068107605 C1 + 0.7852441072463989 C2
#>    + 0.7541319727897644 C3 >= 0.3163650810718537
#>  R3: 0.219966322183609 C0 + 0.2713800370693207 C1 + 0.3296246528625488 C2
#>    + 0.3900085389614105 C3 >= 0.1210979551076889
#>  R4: 0.4533809423446655 C0 + 0.4413638710975647 C1 + 0.4343546628952026 C2
#>    + 0.4355628192424774 C3 >= 0.176466229557991
#> Bounds
#> Binaries
#>  C0 C1 C2 C3
#> End
# }