This is the 7th model in a series of tutorial examples. More...

#include "gams.h"
#include <vector>
#include <iostream>

Functions
string	getModelText ()
	Get model as string.

int	main (int argc, char *argv[])

Detailed Description

This is the 7th model in a series of tutorial examples.

Here we show:

How to create a GAMSModelInstance from a GAMSCheckpoint
How to modify a parameter of a GAMSModelInstance using GAMSModifier
How to modify a variable of a GAMSModelInstance using GAMSModifier

Definition in file transport7.cpp.

Function Documentation

◆ getModelText()

string getModelText ( )

Get model as string.

Definition at line 33 of file transport7.cpp.

{
    return " Sets                                                               \n"
           "     i   canning plants   / seattle, san-diego /                    \n"
           "     j   markets          / new-york, chicago, topeka / ;           \n"
           "                                                                    \n"
           "Parameters                                                          \n"
           "     a(i)  capacity of plant i in cases                             \n"
           "       /    seattle     350                                         \n"
           "            san-diego   600  /                                      \n"
           "                                                                    \n"
           "     b(j)  demand at market j in cases                              \n"
           "       /    new-york    325                                         \n"
           "            chicago     300                                         \n"
           "            topeka      275  / ;                                    \n"
           "                                                                    \n"
           "Table d(i,j)  distance in thousands of miles                        \n"
           "                  new-york       chicago      topeka                \n"
           "    seattle          2.5           1.7          1.8                 \n"
           "    san-diego        2.5           1.8          1.4  ;              \n"
           "                                                                    \n"
           "Scalar f      freight in dollars per case per thousand miles  /90/ ;\n"
           "Scalar bmult  demand multiplier /1/;                                \n"
           "                                                                    \n"
           "Parameter c(i,j)  transport cost in thousands of dollars per case ; \n"
           "                                                                    \n"
           "          c(i,j) = f * d(i,j) / 1000 ;                              \n"
           "                                                                    \n"
           "Variables                                                           \n"
           "     x(i,j)  shipment quantities in cases                           \n"
           "     z       total transportation costs in thousands of dollars ;   \n"
           "                                                                    \n"
           "Positive Variable x ;                                               \n"
           "                                                                    \n"
           "Equations                                                           \n"
           "     cost        define objective function                          \n"
           "     supply(i)   observe supply limit at plant i                    \n"
           "     demand(j)   satisfy demand at market j ;                       \n"
           "                                                                    \n"
           "cost ..        z  =e=  sum((i,j), c(i,j)*x(i,j)) ;                  \n"
           "                                                                    \n"
           "supply(i) ..   sum(j, x(i,j))  =l=  a(i) ;                          \n"
           "                                                                    \n"
           "demand(j) ..   sum(i, x(i,j))  =g=  bmult*b(j) ;                    \n"
           "                                                                    \n"
           "Model transport /all/ ;                                             \n";
}

Referenced by main().

◆ main()

int main	(	int	argc,
		char *	argv[] )

Definition at line 88 of file transport7.cpp.

{
    cout << "---------- Transport 7 --------------" << endl;
 
    try {
        GAMSWorkspaceInfo wsInfo;
        if (argc > 1)
            wsInfo.setSystemDirectory(argv[1]);
        GAMSWorkspace ws(wsInfo);
        GAMSCheckpoint cp = ws.addCheckpoint();
 
        // initialize a GAMSCheckpoint by running a GAMSJob
        GAMSJob t7 = ws.addJobFromString(getModelText());
        t7.run(cp);
 
        // create a GAMSModelInstance and solve it multiple times with different scalar bmult
        GAMSModelInstance mi = cp.addModelInstance();
        GAMSParameter bmult = mi.syncDb().addParameter("bmult", 0, "demand multiplier");
        GAMSOptions opt = ws.addOptions();
        opt.setAllModelTypes("cplex");
 
        // instantiate the GAMSModelInstance and pass a model definition and GAMSModifier to declare bmult mutable
        mi.instantiate("transport use lp min z", opt, GAMSModifier(bmult));
 
        bmult.addRecord().setValue(1.0);
        vector<double> bmultlist = { 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3 };
 
        for (double b : bmultlist) {
            bmult.firstRecord().setValue(b);
            mi.solve();
            cout << "Scenario bmult=" << b << ":" << endl;
            cout << "  Modelstatus: " << mi.modelStatusAsString() << endl;
            cout << "  Solvestatus: " << mi.solveStatusAsString() << endl;
            cout << "  Obj: " << mi.syncDb().getVariable("z").findRecord().level() << endl;
        }
 
        // create a GAMSModelInstance and solve it with single links in the network blocked
        mi = cp.addModelInstance();
 
        GAMSVariable x = mi.syncDb().addVariable("x", 2, GAMSEnum::VarType::Positive, "");
        GAMSParameter xup = mi.syncDb().addParameter("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, GAMSEnum::SymbolUpdateAction::Upper, xup));
 
        for (GAMSSetRecord i : t7.outDB().getSet("i")) {
            for (GAMSSetRecord j : t7.outDB().getSet("j")) {
                xup.clear();
                xup.addRecord(i.key(0), j.key(0)).setValue(0);
                mi.solve();
                cout << "Scenario link blocked=" << i.key(0) << "-" << j.key(0) << endl;
                cout << "  Modelstatus: " << mi.modelStatusAsString() << endl;
                cout << "  Solvestatus: " << mi.solveStatusAsString() << endl;
                cout << "  Obj: " << mi.syncDb().getVariable("z").findRecord().level() << endl;
            }
        }
 
    } catch (GAMSException &ex) {
        cout << "GAMSException occured: " << ex.what() << endl;
    } catch (exception &ex) {
        cout << ex.what() << endl;
    }
 
    return 0;
}

Functions

Detailed Description

Function Documentation

◆ getModelText()

◆ main()