apis/examples_python/transport10_8py_source.html

import os

import sys

from gams import GamsWorkspace

from openpyxl import load_workbook


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';


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


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

$gdxIn %gdxincname%

$load i j a b d

$gdxIn


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)


    wb = load_workbook(

        os.path.join(ws.system_directory, "apifiles", "Data", "transport.xlsx")

    )

    capacity = wb["capacity"]

    demand = wb["demand"]

    distance = wb["distance"]


    # number of markets/plants have to be the same in all spreadsheets

    if (

        distance.max_column - 1 != demand.max_column

        or distance.max_row - 1 != capacity.max_row

    ):

        raise Exception("Size of the spreadsheets doesn't match")


    db = ws.add_database()

    i = db.add_set("i", 1, "Plants")

    j = db.add_set("j", 1, "Markets")

    capacity_param = db.add_parameter_dc("a", [i], "Capacity")

    demand_param = db.add_parameter_dc("b", [j], "Demand")

    distance_param = db.add_parameter_dc("d", [i, j], "Distance")


    for c in capacity.iter_cols():

        key = c[0].value

        i.add_record(key)

        capacity_param.add_record(key).value = c[1].value


    for c in demand.iter_cols():

        key = c[0].value

        j.add_record(key)

        demand_param.add_record(key).value = c[1].value


    for c in range(2, distance.max_column + 1):

        for r in range(2, distance.max_row + 1):

            keys = (

                distance.cell(row=r, column=1).value,

                distance.cell(row=1, column=c).value,

            )

            v = distance.cell(row=r, column=c).value

            distance_param.add_record(keys).value = v


    # create and run the GamsJob

    job = ws.add_job_from_string(GAMS_MODEL)

    opt = ws.add_options()

    opt.defines["gdxincname"] = db.name

    opt.all_model_types = "xpress"

    job.run(opt, databases=db)

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

        print(

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

        )