apis/examples_python/transport5_8py_source.html

import sys

from gams import GamsWorkspace


GAMS_MODEL = """

Set

   i 'canning plants' / seattle,  san-diego /

   j 'markets'        / new-york, chicago, topeka /;


Parameter

   a(i) 'capacity of plant i in cases'

        / seattle    350

          san-diego  600 /


   b(j) 'demand at market j in cases'

        / new-york   325

          chicago    300

          topeka     275 /;


Table d(i,j) 'distance in thousands of miles'

              new-york  chicago  topeka

   seattle         2.5      1.7     1.8

   san-diego       2.5      1.8     1.4;


Scalar

   f     'freight in dollars per case per thousand miles' / 90 /

   bmult 'demand multiplier' / 1 /;


Parameter c(i,j) 'transport cost in thousands of dollars per case';

c(i,j) = f*d(i,j)/1000;


Variable

   x(i,j) 'shipment quantities in cases'

   z      'total transportation costs in thousands of dollars';


Positive Variable x;


Equations

   cost      'define objective function'

   supply(i) 'observe supply limit at plant i'

   demand(j) 'satisfy demand at market j';


cost..      z =e= sum((i,j), c(i,j)*x(i,j));


supply(i).. sum(j, x(i,j)) =l= a(i);


demand(j).. sum(i, x(i,j)) =g= bmult*b(j);


Model transport /all/;


Scalar ms 'model status', ss 'solve status';

"""


if __name__ == "__main__":

    sys_dir = sys.argv[1] if len(sys.argv) > 1 else None

    ws = GamsWorkspace(system_directory=sys_dir)


    cp = ws.add_checkpoint()


    # initialize a GamsCheckpoint by running a GamsJob

    job = ws.add_job_from_string(GAMS_MODEL)

    job.run(checkpoint=cp)


    bmult = [0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3]


    # create a new GamsJob that is initialized from the GamsCheckpoint

    for b in bmult:

        job = ws.add_job_from_string(

            f"bmult={b}; solve transport min z use lp; ms=transport.modelstat; ss=transport.solvestat;",

            cp,

        )

        job.run()

        print(f"Scenario bmult={b}:")

        print(f"  Modelstatus: {job.out_db['ms'].find_record().value}")

        print(f"  Solvestatus: {job.out_db['ss'].find_record().value}")

        print(f"  Obj: {job.out_db['z'].find_record().level}")