transport7.py
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9
10from __future__ import print_function
11from gams import *
12import sys
13
15 return '''
16 Sets
17 i canning plants / seattle, san-diego /
18 j markets / new-york, chicago, topeka / ;
19
20 Parameters
21
22 a(i) capacity of plant i in cases
23 / seattle 350
24 san-diego 600 /
25
26 b(j) demand at market j in cases
27 / new-york 325
28 chicago 300
29 topeka 275 / ;
30
31 Table d(i,j) distance in thousands of miles
32 new-york chicago topeka
33 seattle 2.5 1.7 1.8
34 san-diego 2.5 1.8 1.4 ;
35
36 Scalar f freight in dollars per case per thousand miles /90/ ;
37 Scalar bmult demand multiplier /1/;
38
39 Parameter c(i,j) transport cost in thousands of dollars per case ;
40
41 c(i,j) = f * d(i,j) / 1000 ;
42
43 Variables
44 x(i,j) shipment quantities in cases
45 z total transportation costs in thousands of dollars ;
46
47 Positive Variable x ;
48
49 Equations
50 cost define objective function
51 supply(i) observe supply limit at plant i
52 demand(j) satisfy demand at market j ;
53
54 cost .. z =e= sum((i,j), c(i,j)*x(i,j)) ;
55
56 supply(i) .. sum(j, x(i,j)) =l= a(i) ;
57
58 demand(j) .. sum(i, x(i,j)) =g= bmult*b(j) ;
59
60 Model transport /all/ ; '''
61
62
63if __name__ == "__main__":
64 if len(sys.argv) > 1:
65 ws = GamsWorkspace(system_directory = sys.argv[1])
66 else:
67 ws = GamsWorkspace()
68
69 cp = ws.add_checkpoint()
70
71 # initialize a GAMSCheckpoint by running a GAMSJob
72 t7 = ws.add_job_from_string(get_model_text())
73 t7.run(checkpoint=cp)
74
75 # create a GAMSModelInstance and solve it multiple times with different scalar bmult
76 mi = cp.add_modelinstance()
77 bmult = mi.sync_db.add_parameter("bmult", 0, "demand multiplier")
78 opt = ws.add_options()
79 opt.all_model_types = "cplexd"
80
81 # instantiate the GAMSModelInstance and pass a model definition and GAMSModifier to declare bmult mutable
82 mi.instantiate("transport use lp min z", GamsModifier(bmult), opt)
83
84 bmult.add_record().value = 1.0
85 bmultlist = [ 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3 ]
86
87 for b in bmultlist:
88 bmult.first_record().value = b
89 mi.solve()
90 print("Scenario bmult=" + str(b) + ":")
91 print(" Modelstatus: " + str(mi.model_status))
92 print(" Solvestatus: " + str(mi.solver_status))
93 print(" Obj: " + str(mi.sync_db.get_variable("z").find_record().level))
94
95
96 # create a GAMSModelInstance and solve it with single links in the network blocked
97 mi = cp.add_modelinstance()
98 x = mi.sync_db.add_variable("x", 2, VarType.Positive)
99 xup = mi.sync_db.add_parameter("xup", 2, "upper bound on x")
100
101 # instantiate the GAMSModelInstance and pass a model definition and GAMSModifier to declare upper bound of X mutable
102 mi.instantiate("transport use lp min z", GamsModifier(x, UpdateAction.Upper, xup))
103 mi.solve()
104
105 for i in t7.out_db["i"]:
106 for j in t7.out_db["j"]:
107 xup.clear()
108 xup.add_record((i.key(0),j.key(0))).value = 0
109 mi.solve()
110 print("Scenario link blocked: " + i.key(0) + " - " + j.key(0))
111 print(" Modelstatus: " + str(mi.model_status))
112 print(" Solvestatus: " + str(mi.solver_status))
113 print(" Obj: " + str(mi.sync_db["z"].find_record().level))
114
115
def get_model_text()
Definition: transport7.py:14