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SummedObjectivesLpSolver

Info

Example dummy solver that sums multiple objectives.

Source code in examples/summing/SummedObjectivesLpSolver.py 
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class SummedObjectivesLpSolver(LpSolver):
    """

    Info:
        Example dummy solver that sums multiple objectives.

    """

    def __init__(self):
        super().__init__()

    def actualSolve(self, lp: MultiObjectiveLpProblem):
        """
        Parameters:
            lp: Instance of MultiObjectiveLpProblem
        """
        lp.objective = lpSum(lp.objectives)
        return LpSolverDefault.actualSolve(lp)

Code examples:

Warehouse cost example 
from model.multi_objective_lp import MultiObjectiveLpProblem
from pulp import LpVariable, lpSum
from examples.summing.SummedObjectivesLpSolver import SummedObjectivesLpSolver

# we are building only one warehouse
warehouses_to_build = 1

# define the costs for the warehouse choices
warehouse_fixed_costs = [100, 120, 80]
cost_per_km = [3, 3, 3]
distances = [20, 30, 45]
transport_costs = [cost * dist for cost, dist in zip(cost_per_km, distances)]
warehouses = ['1', '2', '3']

model = MultiObjectiveLpProblem(name='warehouse')

build_warehouse_flag = LpVariable.matrix("build", warehouses, cat="Binary", lowBound=0)

model += lpSum(build_warehouse_flag) == warehouses_to_build

# cost to be minimized
transport_obj = lpSum([trans_cost * flag for trans_cost, flag in zip(transport_costs, build_warehouse_flag)])
fix_obj = lpSum([fix_cost * flag for fix_cost, flag in zip(warehouse_fixed_costs, build_warehouse_flag)])

model.setObjectives([transport_obj, fix_obj])
model.solve(solver=SummedObjectivesLpSolver())