apis/examples_python/transport__gt_8py_source.html

from gams import *

import gamstransfer as gt

import numpy as np

import sys

import os


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 gdxincname $abort "no include file name for data file provided"

$gdxin %gdxincname%

$load i j a b d 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";


Scalar

     bmult       "demand multiplier" /1/;


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/;


Solve transport using lp minimizing z;'''


if __name__ == "__main__":

    if len(sys.argv) > 1:

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

    else:

        ws = GamsWorkspace(working_directory='.')


    m = gt.Container()

    i = m.addSet('i', records=[ "Seattle", "San-Diego" ])

    j = m.addSet('j', records=[ "New-York", "Chicago", "Topeka" ])

    m.addParameter('a', [i], records=np.array([350, 600]))

    m.addParameter('b', [j], records=np.array([325, 300, 275]))

    m.addParameter('d', [i,j], records=np.array([[2.5, 1.7, 1.8],

                                                 [2.5, 1.8, 1.4]]))

    m.addParameter('f', records=90)


    tm = ws.add_job_from_string(get_model_text())

    opt = ws.add_options()

    opt.defines["gdxincname"] = "gtin.gdx"

    opt.all_model_types = "xpress"

    opt.gdx = "gtout.gdx"


    m.write(os.path.join(ws.working_directory, opt.defines["gdxincname"]))

    cp = ws.add_checkpoint()

    tm.run(gams_options=opt, checkpoint=cp, create_out_db=False)

    tmOut = gt.Container(os.path.join(ws.working_directory, opt.gdx))


    # create a GAMSModelInstance and solve it multiple times with different scalar bmult

    mi = cp.add_modelinstance()

    bmult = mi.sync_db.add_parameter("bmult", 0, "demand multiplier")

    opt = ws.add_options()

    opt.all_model_types = "cplex"


    # instantiate the GAMSModelInstance and pass a model definition and GAMSModifier to declare bmult mutable

    mi.instantiate("transport use lp min z", GamsModifier(bmult), opt)


    bmult.add_record().value = 1.0

    bmultlist = [ 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3 ]


    m = gt.Container()

    gt_bmult = m.addParameter('bmult', records=1.0);

    for b in bmultlist:

        gt_bmult.setRecords(b)

        m.write(mi.sync_db)

        mi.solve()

        mOut = gt.Container(mi.sync_db)

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

        print("  Modelstatus: " + str(mi.model_status))

        print("  Solvestatus: " + str(mi.solver_status))

        print("  Obj: " + str(mOut.data['z'].records['level'].iloc[0]))


    # create a GAMSModelInstance and solve it with single links in the network blocked

    mi = cp.add_modelinstance()

    x = mi.sync_db.add_variable("x", 2, VarType.Positive)

    xup = mi.sync_db.add_parameter("xup", 2, "upper bound on x")


    # instantiate the GAMSModelInstance and pass a model definition and GAMSModifier to declare upper bound of X mutable

    mi.instantiate("transport use lp min z", GamsModifier(x, UpdateAction.Upper, xup))

    mi.solve()


    m = gt.Container()

    gt_xup = m.addParameter('xup', ['i','j']);

    for i in tmOut.data['i'].records['i_0']:

        for j in tmOut.data['j'].records['j_0']:

            gt_xup.setRecords([(i,j,-0.0)]) # -0.0 turns the 0 into an EPS

            m.write(mi.sync_db)

            mi.solve()

            mOut = gt.Container(mi.sync_db)

            print("Scenario link blocked: " + i + " - " + j)

            print("  Modelstatus: " + str(mi.model_status))

            print("  Solvestatus: " + str(mi.solver_status))

            print("  Obj: " + str(mOut.data['z'].records['level'].iloc[0]))