prioritizr (version 4.1.5)

portfolios: Solution portfolios

Description

Conservation planners often desire a portfolio of solutions to present to decision makers. This is because conservation planners often do not have access to "perfect" information, such as cost data that accurately reflects stakeholder preferences, and so having multiple near-optimal solutions can be a useful.

Details

All methods for generating portfolios will return solutions that are within the specified optimality gap.

The following portfolios can be added to a conservation planning problem:

add_default_portfolio

Generate a single solution.

add_cuts_portfolio

Generate a portfolio of distinct solutions within a pre-specified optimality gap using Bender's cuts.

add_pool_portfolio

Generate a portfolio of solutions by extracting all the feasible solutions discovered during the optimization process.

add_shuffle_portfolio

Generate a portfolio of solutions by randomly reordering the data prior to attempting to solve the problem.

See Also

constraints, decisions, objectives penalties, problem, solvers, targets.

Examples

# 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() %>%
     add_default_solver(gap = 0.02, verbose = FALSE)

# create problem with cuts portfolio
p1 <- p %>% add_cuts_portfolio(4)

# create problem with shuffle portfolio
p2 <- p %>% add_shuffle_portfolio(4)
# }
# NOT RUN {
# create problem with pool portfolio
p3 <- p %>% add_pool_portfolio()

# solve problems and create solution portfolios
s <- list(solve(p1), solve(p2), solve(p3))

# plot solutions from cuts portfolio
plot(stack(s[[1]]), axes = FALSE, box = FALSE)

# plot solutions from shuffle portfolio
plot(stack(s[[2]]), axes = FALSE, box = FALSE)

# plot solutions from pool portfolio
plot(stack(s[[3]]), axes = FALSE, box = FALSE)
# }