apis/examples_python/transport__class_8py_source.html

from gams import SolveLink


class Transport():


    def __init__(self, ws):


        self._ws = ws

        self.opt = ws.add_options()


        self._dbin1 = ws.add_database(in_model_name = "dbIn1")

        self._dbin2 = ws.add_database(in_model_name = "dbIn2")


        self.opt.solvelink = SolveLink.LoadLibrary

        self.opt.all_model_types = "Cplex"

        self.opt.defines["dbOut1"] = "dbOut1"


        self.i = self._dbin1.add_set("i", 1, "canning plants")

        self.j = self._dbin1.add_set("j", 1, "markets")

        self.a = self._dbin1.add_parameter_dc("a", [self.i], "capacity of plant i in cases")

        self.b = self._dbin1.add_parameter_dc("b", [self.j], "demand at market j in cases")

        self.d = self._dbin1.add_parameter_dc("d", [self.i, self.j], "distance in thousands of miles")

        self.f = self._dbin2.add_parameter("f", 0, "freight in dollars per case per thousand miles")

        self.x = None

        self.z = None


        self._job = ws.add_job_from_string(self.get_model_source())


    def get_model_source(self):

        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 dbIn1 $abort 'no file name for in-database 1 file provided'

$gdxin %dbIn1%

$load i j a b d


$if not set dbIn2 $abort 'no file name for in-database 2 file provided'

$gdxin %dbIn2%

$load f

$gdxin


  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 ;


$if not set dbOut1 $abort 'no file name for out-database 1 file provided'

  execute_unload '%dbOut1%', x, z;

'''


    def run(self, checkpoint=None, output=None):

        self._job.run(self.opt, checkpoint, output, False, [self._dbin1, self._dbin2])


        self._dbout1 = self._ws.add_database_from_gdx(self.opt.defines["dbOut1"] + ".gdx")

        self.x = self._dbout1.get_variable("x")

        self.z = self._dbout1.get_variable("z")