apis/examples_python/transport5_8py_source.html

from gams import GamsWorkspace

import sys


def get_model_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/ ;

  Scalar bmult  demand multiplier /1/;


  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=  bmult*b(j) ;


  Model transport /all/ ;

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


if __name__ == "__main__":

    if len(sys.argv) > 1:

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

    else:

        ws = GamsWorkspace()


    cp = ws.add_checkpoint()


    # initialize a GAMSCheckpoint by running a GAMSJob

    t5 = ws.add_job_from_string(get_model_text())

    t5.run(checkpoint=cp)


    bmultlist = [ 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 bmultlist:

        t5 = ws.add_job_from_string("bmult=" + str(b) + "; solve transport min z use lp; ms=transport.modelstat; ss=transport.solvestat;", cp)

        t5.run()

        print("Scenario bmult=" + str(b) + ":")

        print("  Modelstatus: " + str(t5.out_db["ms"].find_record().value))

        print("  Solvestatus: " + str(t5.out_db["ss"].find_record().value))

        print("  Obj: " + str(t5.out_db["z"].find_record().level))