25.3 Integrals

The Integrator../ns-2/integrator.h supports the approximation of (continuous) integration by (discrete) sums; it is defined in ~ns/integrator.h as

{\rm From integrator.h:}
        class Integrator : public TclObject {
        public:
                Integrator();
                void set(double x, double y);
                void newPoint(double x, double y);
                int command(int argc, const char*const* argv);
        protected:
                double lastx_;
                double lasty_;
                double sum_;
        };

{\rm From integrator.cc:}
        Integrator::Integrator() : lastx_(0.), lasty_(0.), sum_(0.)
        {
                bind("lastx_", &lastx_);
                bind("lasty_", &lasty_);
                bind("sum_", &sum_);
        }

        void Integrator::set(double x, double y)
        {
                lastx_ = x;
                lasty_ = y;
                sum_ = 0.;
        }

        void Integrator::newPoint(double x, double y)
        {
                sum_ += (x - lastx_) * lasty_;
                lastx_ = x;
                lasty_ = y;
        }

        int Integrator::command(int argc, const char*const* argv)
        {
                if (argc == 4) {
                        if (strcmp(argv[1], "newpoint") == 0) {
                                double x = atof(argv[2]);
                                double y = atof(argv[3]);
                                newPoint(x, y);
                                return (TCL_OK);
                        }
                }
                return (TclObject::command(argc, argv));
        }

This class provides a base class used by other classes such as QueueMonitor that keep running sums. Each new element of the running sum is added by the [x, y]newPoint function. After the $k$th execution of newPoint, the running sum is equal to $\sum_{i=1}^{k}y_{i-1}(x_i - x_{i-1})$ where $x_0 = y_0 = 0$ unless lastx
_, lasty
_, or sum
_ are reset via OTcl. Note that a new point in the sum can be added either by the C++ member newPoint or the OTcl member newpoint. The use of integrals to compute certain types of averages (e.g. mean queue lengths) is given in (pp. 429-430, [15]).