This is the 8th model in a series of tutorial examples. More...

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

Functions
void	scenSolve (GAMSWorkspace ws, GAMSCheckpoint cp, vector< double > bmultVector, std::mutex vectorMutex, std::mutex *ioMutex)
	Solve the model in different scenarios.

string	getModelText ()
	Get model as string.

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

Detailed Description

This is the 8th model in a series of tutorial examples.

Here we show:

How to use a vector to solve multiple GAMSModelInstances in parallel

Definition in file transport8.cpp.

Function Documentation

◆ getModelText()

string getModelText ( )

Get model as string.

Definition at line 74 of file transport8.cpp.

{
    return "Sets                                                                  \n"
           "   i   canning plants / seattle, san-diego /                          \n"
           "   j   markets / new-york, chicago, topeka / ;                        \n"
           "                                                                      \n"
           "Parameters                                                            \n"
           "                                                                      \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 128 of file transport8.cpp.

{
    cout << "---------- Transport 8 --------------" << 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
        ws.addJobFromString(getModelText()).run(cp);
 
        vector<double> bmultVector = { 1.3, 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, 0.6 };
        int nrThreads = 2;
        // solve multiple model instances in parallel
        std::mutex vectorMutex;
        std::mutex ioMutex;
        vector<thread> v;
        for (int i = 0; i < nrThreads; i++)
            v.emplace_back([&ws, &cp, &bmultVector, &vectorMutex, &ioMutex] {scenSolve(&ws, &cp, &bmultVector, &vectorMutex, &ioMutex);});
        for (auto& t : v)
            t.join();
 
    } catch (GAMSException &ex) {
        cout << "GAMSException occured: " << ex.what() << endl;
    } catch (exception &ex) {
        cout << ex.what() << endl;
    }
 
    return 0;
}

◆ scenSolve()

void scenSolve	(	GAMSWorkspace *	ws,
		GAMSCheckpoint *	cp,
		vector< double > *	bmultVector,
		std::mutex *	vectorMutex,
		std::mutex *	ioMutex )

Solve the model in different scenarios.

Definition at line 35 of file transport8.cpp.

{
    unique_lock<mutex> vectorLock(*vectorMutex);
    GAMSModelInstance mi = cp->addModelInstance();
    vectorLock.unlock();
 
    GAMSParameter bmult = mi.syncDb().addParameter("bmult", "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);
 
    while (true)
    {
        double b;
 
        // dynamically get a bmult value from the vector instead of passing it to the different threads at creation time
        vectorLock.lock();
        if (bmultVector->empty())
            return;
        b = bmultVector->back();
        bmultVector->pop_back();
        vectorLock.unlock();
        bmult.firstRecord().setValue(b);
        mi.solve();
 
        // we need to make the output a critical section to avoid messed up report informations
        unique_lock<mutex> ioLock(*ioMutex);
        cout << "Scenario bmult=" << b << ":" << endl;
        cout << "  Modelstatus: " << mi.modelStatus() << endl;
        cout << "  Solvestatus: " << mi.solveStatus() << endl;
        cout << "  Obj: " << mi.syncDb().getVariable("z").findRecord().level() << endl;
        ioLock.unlock();
    }
}

Functions

Detailed Description

Function Documentation

◆ getModelText()

◆ main()

◆ scenSolve()