apis/examples_python/transport__gdx_8py_source.html

from gams import *

import sys

import subprocess

import os


if __name__ == "__main__":

    if len(sys.argv) > 1:

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

    else:

        ws = GamsWorkspace()


    # Python lists and dictionaries holding the data

    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

               }


    # create new GamsDatabase instance

    db = ws.add_database()


    # add 1-dimensional set 'i' with explanatory text 'canning plants' to the GamsDatabase

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

    for p in plants:

        i.add_record(p)


    # add 1-dimensional set 'j' with explanatory text 'markets' to the GamsDatabase

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

    for m in markets:

        j.add_record(m)


    # add parameter 'a' with domain 'i'

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

    for p in plants:

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


    # add parameter 'b' with domain 'j'

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

    for m in markets:

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


    # add parameter 'd' with domains 'i' and 'j'

    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


    # add scalar 'f'

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

    f.add_record().value = 90


    # export the GamsDatabase to a GDX file with name 'data.gdx' located in the 'working_directory' of the GamsWorkspace

    db.export("data.gdx")


    print("Content of GDX file 'data.gdx':")

    subprocess.call(["gdxdump", os.path.join(ws.working_directory, "data.gdx")])


    # add a new GamsDatabase and initialize it from the GDX file just created

    db2 = ws.add_database_from_gdx("data.gdx")


    # read data from symbols into Python data structures

    i = [ rec.keys[0] for rec in db2["i"] ]

    j = [ rec.keys[0] for rec in db2["j"] ]


    a = { rec.keys[0]:rec.value     for rec in db2["a"] }

    b = { rec.keys[0]:rec.value     for rec in db2["b"] }

    d = { tuple(rec.keys):rec.value for rec in db2["d"] }


    f = db2["f"].first_record().value


    print("i:")

    for rec in i:

        print("  ", rec)

    print("j:")

    for rec in j:

        print("  ", rec)

    print("a:")

    for rec in a:

        print("  ", rec, ":", a[rec])

    print("b:")

    for rec in b:

        print("  ", rec, ":", b[rec])

    print("d:")

    for rec in d:

        print("  ", rec, ":", d[rec])

    print("f:")

    print("  ", f)