apis/examples_python/transport2_8py_source.html

from gams import *

import os

import sys


def get_data_text():

    return '''

  Sets

       i   canning plants   / seattle, san-diego /

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


  Parameters


       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/ ; '''


def get_model_text():

    return '''

  Sets

       i   canning plants

       j   markets


  Parameters

       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;


$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 ;


  Variables

       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__":

    if len(sys.argv) > 1:

        ws = GamsWorkspace(system_directory = sys.argv[1])

    else:

        ws = GamsWorkspace()


    file = open(os.path.join(ws.working_directory, "tdata.gms"), "w")

    file.write(get_data_text())

    file.close()


    t2 = ws.add_job_from_string(get_model_text())

    opt = ws.add_options()

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

    t2.run(opt)

    for rec in t2.out_db["x"]:

        print("x(" + rec.key(0) + "," + rec.key(1) + "): level=" + str(rec.level) + " marginal=" + str(rec.marginal))