apis/examples_python/transport2_8py_source.html

import os

import sys

from gams import GamsWorkspace


GAMS_DATA = """

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 /;

"""


GAMS_MODEL = """

Set

   i 'canning plants'

   j 'markets';


Parameter

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

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

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


$if not set incname $abort 'no include file name for data file provided'

$include %incname%


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= b(j);


Model transport /all/;


solve transport using lp minimizing z;


display x.l, x.m;

"""


if __name__ == "__main__":

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

    work_dir = sys.argv[2] if len(sys.argv) > 2 else None

    ws = GamsWorkspace(system_directory=sys_dir, working_directory=work_dir)


    with open(os.path.join(ws.working_directory, "tdata.gms"), "w") as file:

        file.write(GAMS_DATA)


    job = ws.add_job_from_string(GAMS_MODEL)

    opt = ws.add_options()

    opt.defines["incname"] = "tdata"

    job.run(opt)

    for rec in job.out_db["x"]:

        print(

            f"x({rec.key(0)},{rec.key(1)}): level={rec.level} marginal={rec.marginal}"

        )