I am learning the GAMS API by attempting to re-implement some of the example programs given in GAMS language.
I seem to be a bit stuck at adding records to equations. In the following code, I am unsure what to do after adding equation cost to the db.
There does not seem to be a mechanism by which to
int transpo(void)
{
static constexpr auto plants = {"seattle", "san-diego"};
static constexpr double capacity[2] = {350., 600.};
static constexpr auto markets = {"new-york, chicago, topeka"};
static constexpr double demand[3] = {325, 300, 275};
static constexpr double distances[2][3] = {
{2.5, 1.7, 1.8},
{2.5, 1.8, 1.4}
};
GAMSWorkspace ws;
GAMSDatabase db = ws.addDatabase();
auto i = db.addSet("i", 1, "canning plants");
for (auto& plant : plants) i.addRecord(plant);
auto j = db.addSet("j", 1, "markets");
for (auto& market : markets) j.addRecord(market);
auto a = db.addParameter("a", "capacity of plant i in cases", i);
for (auto it = plants.begin(); it != plants.end(); ++it) {
const auto idx = it - plants.begin();
a.addRecord(*it).setValue(capacity[idx]);
}
auto b = db.addParameter("b", "demand at market j in cases", j);
for (auto it = markets.begin(); it != markets.end(); ++it) {
const auto idx = it - markets.begin();
b.addRecord(*it).setValue(capacity[idx]);
}
auto d = db.addParameter("d", "distance in thousands of miles", i, j);
for (auto pit = plants.begin(); pit != plants.end(); ++pit) {
const auto pidx = pit - plants.begin();
for (auto mit = markets.begin(); mit != markets.end(); ++mit) {
const auto midx = mit - markets.begin();
d.addRecord(*pit, *mit).setValue(distances[pidx][midx]);
}
}
auto f = db.addParameter("f",
"freight in dollars per case per thousand miles");
f.addRecord().setValue(90);
auto c = db.addParameter("c",
"transport cost in thousands of dollars per case", i, j);
for (auto pit = plants.begin(); pit != plants.end(); ++pit) {
const auto pidx = pit - plants.begin();
for (auto mit = markets.begin(); mit != markets.end(); ++mit) {
const auto midx = mit - markets.begin();
c.addRecord(*pit, *mit).setValue(
d.findRecord(*pit, *mit).value() * f.findRecord().value());
}
}
auto x = db.addVariable("x", gams::GAMSEnum::Positive,
"sipment quantities in cases", i, j);
auto z = db.addVariable("z", gams::GAMSEnum::Free,
"total transportation cost in thousands of dollars");
auto cost = db.addEquation("cost", gams::GAMSEnum::E,
"define objective function");
/* cost.. z =e= sum((i, j), c(i, j)*x(i, j)) ; */
cost.addRecord(). /* What goes here??? */
return 0;
}