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facilitylocation.py
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facilitylocation.py
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from gurobipy import *
class FacilityLocationModel:
def __init__(self, data):
"""
args:
data: dictionary
Data must have following data
under corresponding key
'periodid': List of all period ids
for single or mult-period model
'siteid': List of all unique ids
representing sites
'customerid': List of all unique ids
representing customers
'sitecapbyperiod': Dictionary of dictionary
with site capacity as format -
{
periodid: {
siteid: int/float,
},
}
'siteslackcapbyperiod': Dictionary of
dictionary with site slack capacity
as format -
{
periodid: {
siteid: int/float,
},
}
'customerdembyperiod': Dictionary of
dictionary with customer demand
as format -
{
periodid: {
customerid: int/float,
},
}
'servicedist': Dictionary containing
distance (or another related measure)
for all combinations of
siteid and customerid as tuple
keys -
{
(siteid, custid): int/float,
}
'maxopensites': int representing maximum
number of sites that can be open
throughout horizon. This is not exactly
same as saying max number of sites
open at any given period.
Uses Gurobi Python API for creating model and
solving. Requires gurobi license. Read more @
https://www.gurobi.com/
"""
try:
self.periodid = data['periodid']
self.siteid = data['siteid']
self.customerid = data['customerid']
self.sitecapbyperiod = data['sitecapbyperiod']
self.siteslackcapbyperiod = data['siteslackcapbyperiod']
self.customerdembyperiod = data['customerdembyperiod']
self.servicedist = data['servicedist']
self.maxopensites = data['maxopensites']
except KeyError as e:
raise KeyError(f"Missing required data {e}")
def modelProblem(self, exportmps=False):
"""
Method models basic facility location
with slack capacity for sites.
Uses Gurobi's python API through gurobipy
for creating model.
args:
exportmps: boolean
If true, formulation is exported
as model.mps file.
"""
try:
self.model = Model("Facility Location")
# variables
flow = self.model.addVars(
self.periodid,
self.siteid,
self.customerid,
vtype=GRB.CONTINUOUS,
lb=0,
name='flow')
flowindicator = self.model.addVars(
self.periodid,
self.siteid,
self.customerid,
vtype=GRB.BINARY,
name='flowindicator')
serviceindicator = self.model.addVars(
self.periodid,
self.siteid,
vtype=GRB.BINARY,
name='serviceindicator')
siteindicator = self.model.addVars(
self.siteid,
vtype=GRB.BINARY,
name='siteindicator')
slackcap = self.model.addVars(
self.periodid,
self.siteid,
vtype=GRB.CONTINUOUS,
lb=0,
name='slackcap')
# objective
self.model.setObjective(
sum(self.servicedist[i,j]*flowindicator[p,i,j]
for p in self.periodid
for i in self.siteid
for j in self.customerid)
+ sum(0.1*self.servicedist[i,j]*flow[p,i,j]
for p in self.periodid
for i in self.siteid
for j in self.customerid)
+ 0.25*sum(slackcap[p,i]
for p in self.periodid
for i in self.siteid)
,
sense=GRB.MINIMIZE
)
# constraints
self.model.addConstrs(
sum(flow[p,i,j] for i in self.siteid)
== self.customerdembyperiod[p][j]
for p in self.periodid
for j in self.customerid
)
self.model.addConstrs(
(flowindicator[p,i,j] == 0) >>
(flow[p,i,j] == 0)
for p in self.periodid
for i in self.siteid
for j in self.customerid
)
self.model.addConstrs(
(serviceindicator[p,i] == 0) >>
(flow[p,i,j] == 0)
for p in self.periodid
for i in self.siteid
for j in self.customerid
)
self.model.addConstrs(
(siteindicator[i] == 0) >>
(serviceindicator[p,i] == 0)
for p in self.periodid
for i in self.siteid
)
# Max additional 1 site, existing 3
self.model.addConstr(
sum(siteindicator[i] for i in self.siteid)
<= self.maxopensites
)
self.model.addConstrs(
sum(flow[p,i,j] for j in self.customerid)
<= self.sitecapbyperiod[p][i] \
+ slackcap[p,i]
for p in self.periodid
for i in self.siteid
)
#max slack
self.model.addConstrs(
slackcap[p,i] \
<= self.siteslackcapbyperiod[p][i]
for p in self.periodid
for i in self.siteid
)
except GurobiError as e:
print(f"Gurobi Error occured {e}")
if exportmps:
self.model.write('model.mps')
def setParameters(self):
"""
Method to set parameters -
MIP Gap 1%
Logfile name gurobilog.txt
"""
self.model.setParam(GRB.Param.MIPGap, 0.01)
self.model.setParam(GRB.Param.LogFile, "gurobilog.txt")
def solveModel(self):
"""
Method to call to solve
"""
self.model.optimize()
def extractSolution(self):
"""
Method to extract primary decision that are
flows from a solved model.
"""
if self.model.status == GRB.Status.SUBOPTIMAL or \
self.model.status == GRB.Status.OPTIMAL:
flows = {}
objectivecontri = {}
for pid in self.periodid:
for sid in self.siteid:
for cid in self.customerid:
flow = self.model.getVarByName(
f"flow[{pid},{sid},{cid}]"
).X
flows[(pid, sid, cid)] = flow
objectivecontri[(pid, sid, cid)] = \
0.1 * self.servicedist[sid, cid] * flow \
+ (self.servicedist[sid, cid] if flow > 0 else 0)
return flows, objectivecontri
else:
print("Model might not have solution available")
return {}, {}