10from gams
import GamsWorkspace, GamsModifier, UpdateAction, VarType
14 i 'canning plants' / seattle, san-diego /
15 j 'markets' / new-york, chicago, topeka /;
18 a(i) 'capacity of plant i in cases'
22 b(j) 'demand at market j in cases'
27Table d(i,j) 'distance in thousands of miles'
28 new-york chicago topeka
30 san-diego 2.5 1.8 1.4;
33 f 'freight in dollars per case per thousand miles' / 90 /
34 bmult 'demand multiplier' / 1 /;
36Parameter c(i,j) 'transport cost in thousands of dollars per case';
37c(i,j) = f*d(i,j)/1000;
40 x(i,j) 'shipment quantities in cases'
41 z 'total transportation costs in thousands of dollars';
46 cost 'define objective function'
47 supply(i) 'observe supply limit at plant i'
48 demand(j) 'satisfy demand at market j';
50cost.. z =e= sum((i,j), c(i,j)*x(i,j));
52supply(i).. sum(j, x(i,j)) =l= a(i);
54demand(j).. sum(i, x(i,j)) =g= bmult*b(j);
59if __name__ ==
"__main__":
60 sys_dir = sys.argv[1]
if len(sys.argv) > 1
else None
61 work_dir = sys.argv[2]
if len(sys.argv) > 2
else None
62 ws = GamsWorkspace(system_directory=sys_dir, working_directory=work_dir)
64 cp = ws.add_checkpoint()
67 job = ws.add_job_from_string(GAMS_MODEL)
68 job.run(checkpoint=cp)
71 mi = cp.add_modelinstance()
72 bmult = mi.sync_db.add_parameter(
"bmult", 0,
"demand multiplier")
73 opt = ws.add_options()
74 opt.all_model_types =
"cplex"
77 mi.instantiate(
"transport use lp min z", GamsModifier(bmult), opt)
79 bmult.add_record().value = 1.0
80 bmult_list = [0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3]
83 bmult.first_record().value = b
85 print(f
"Scenario bmult={b}:")
86 print(f
" Modelstatus: {mi.model_status}")
87 print(f
" Solvestatus: {mi.solver_status}")
88 print(f
" Obj: {mi.sync_db['z'].first_record().level}")
91 mi = cp.add_modelinstance()
92 x = mi.sync_db.add_variable(
"x", 2, VarType.Positive)
93 xup = mi.sync_db.add_parameter(
"xup", 2,
"upper bound on x")
96 mi.instantiate(
"transport use lp min z", GamsModifier(x, UpdateAction.Upper, xup))
99 for i
in job.out_db[
"i"]:
100 for j
in job.out_db[
"j"]:
102 xup.add_record((i.key(0), j.key(0))).value = 0
104 print(f
"Scenario link blocked: {i.key(0)} - {j.key(0)}")
105 print(f
" Modelstatus: {mi.model_status}")
106 print(f
" Solvestatus: {mi.solver_status}")
107 print(f
" Obj: {mi.sync_db['z'].find_record().level}")