apis/examples_python/transport11_8py_source.html

from gams import *

import os

import sys


def get_base_model_text():

    return '''

$onempty

  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 /0/;


  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 ; '''


def get_model_text():

    return '''

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

$gdxin %gdxincname%

$onMulti

$load i j a b d f

$gdxin


  Display x.l, x.m ; '''


def create_save_restart(cp_file_name):

    if len(sys.argv) > 1:

        ws = GamsWorkspace(os.path.dirname(cp_file_name), sys.argv[1])

    else:

        ws = GamsWorkspace(os.path.dirname(cp_file_name))


    j1 = ws.add_job_from_string(get_base_model_text())

    opt = ws.add_options()


    opt.action = Action.CompileOnly

    cp = ws.add_checkpoint(os.path.basename(cp_file_name))

    j1.run(opt, cp)

    del opt


if __name__ == "__main__":

    # Create a save/restart file usually supplied by an application provider

    # We create it for demonstration purpose

    w_dir = os.path.join(".", "tmp")

    create_save_restart(os.path.join(w_dir, "tbase"));


    plants   = [ "Seattle", "San-Diego" ]

    markets  = [ "New-York", "Chicago", "Topeka" ]

    capacity = { "Seattle": 350.0, "San-Diego": 600.0 }

    demand   = { "New-York": 325.0, "Chicago": 300.0, "Topeka": 275.0 }


    distance = { ("Seattle",   "New-York") : 2.5,

                 ("Seattle",   "Chicago")  : 1.7,

                 ("Seattle",   "Topeka")   : 1.8,

                 ("San-Diego", "New-York") : 2.5,

                 ("San-Diego", "Chicago")  : 1.8,

                 ("San-Diego", "Topeka")   : 1.4

               }


    if len(sys.argv) > 1:

        ws = GamsWorkspace(w_dir, sys.argv[1])

    else:

        ws = GamsWorkspace(w_dir)


    db = ws.add_database()


    # prepare a GAMSDatabase with data from the Python data structures

    i = db.add_set("i", 1, "canning plants")

    for p in plants:

        i.add_record(p)


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

    for m in markets:

        j.add_record(m)


    a = db.add_parameter_dc("a", [i], "capacity of plant i in cases")

    for p in plants:

        a.add_record(p).value = capacity[p]


    b = db.add_parameter_dc("b", [j], "demand at market j in cases")

    for m in markets:

        b.add_record(m).value = demand[m]


    d = db.add_parameter_dc("d", [i,j], "distance in thousands of miles")

    for k, v in iter(distance.items()):

        d.add_record(k).value = v


    f = db.add_parameter("f", 0, "freight in dollars per case per thousand miles")

    f.add_record().value = 90


    # run a job using data from the created GAMSDatabase

    cp_base = ws.add_checkpoint("tbase")

    t4 = ws.add_job_from_string(get_model_text(), cp_base)

    opt = ws.add_options()

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

    opt.all_model_types = "xpress"

    t4.run(opt, databases=db)


    for rec in t4.out_db["x"]:

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