JKQtPlotter

Plotting Mathematical Functions as Line Graphs

This project (see ./test/simpletest_functionplot/) demonstrates how to plot mathematical functions as line graphs. The functions may be defined as static C functions, C++ functors or c++ inline functions. See test/simpletest_parsedfunctionplot for an example of how to use an internal equation parser provided with JKQtPlotter instead of directly defining functions.

The first example shows how to plot a C++ inline function:

    JKQTPxFunctionLineGraph* func1=new JKQTPxFunctionLineGraph(plot);
    func1->set_plotFunction([](double x, void* /*params*/) { return 0.2*x*x-0.015*x*x*x; });
    func1->set_title("C++-inline function $0.2x^2-0.015x^3$");
    plot->addGraph(func1);

In any such plot function, you can also use parameters, provided via the second parameter. Usually these are "internal parameters", defined by func2->set_paramsV(p0, p1, ...):

    JKQTPxFunctionLineGraph* func2=new JKQTPxFunctionLineGraph(plot);
    func2->set_plotFunction([](double x, void* params) {
        QVector<double>* p=static_cast<QVector<double>*>(params);
        return p->at(0)*sin(2.0*M_PI*x*p->at(1));
    });
    // here we set the parameters p0, p1
    func2->set_paramsV(5, 0.2);
    func2->set_title("C++-inline function with int. params $p_0\\cdot\\sin(x*2.0*\\pi\\cdot p_1)$");
    plot->addGraph(func2);

... but generally any pointer can be used as parameter (the set by set_parameter(static_cast<void*>(myDataObject))):

    JKQTPxFunctionLineGraph* func3=new JKQTPxFunctionLineGraph(plot);
    func3->set_plotFunction([](double x, void* params) {
        QMap<QString,double>* p=static_cast<QMap<QString,double>*>(params);
        return p->value("amplitude")*sin(2.0*M_PI*x*p->value("frequency"));
    });
    // here we set the parameters p0, p1
    QMap<QString,double> params3;
    params3["amplitude"]=-3;
    params3["frequency"]=0.3;
    func3->set_params(&params3);
    func3->set_title("C++-inline function with ext. params $p_0\\cdot\\sin(x*2.0*\\pi\\cdot p_1)$");
    plot->addGraph(func3);

You can also use C++ functors (or function objects):

    struct SincSqr {
    public:
        inline SincSqr(double amplitude): a(amplitude) {}
        inline double operator()(double x, void* /*params*/) {
            return a*sin(x)*sin(x)/x/x;
        }
    private:
        double a;
    };

    // ...
    
    JKQTPxFunctionLineGraph* func4=new JKQTPxFunctionLineGraph(plot);
    func4->set_plotFunction(SincSqr(-8));
    func4->set_title("C++ functor $-8*\\sin^2(x)/x^2$");
    plot->addGraph(func4);

... or simple static C functions:

    double sinc(double x, void* /*params*/) {
        return 10.0*sin(x)/x;
    }
    
    // ...

    JKQTPxFunctionLineGraph* func5=new JKQTPxFunctionLineGraph(plot);
    func5->set_plotFunction(&sinc);
    func5->set_title("static C function $10*\\sin(x)/x$");
    plot->addGraph(func5);

Finally JKQTPxFunctionLineGraph provides a small set of special functions (polynomial, exponential, ...), which draw their parameters from the internal or external parameters:

    JKQTPxFunctionLineGraph* func6=new JKQTPxFunctionLineGraph(plot);
    func6->setSpecialFunction(JKQTPxFunctionLineGraph::Line);
    // here we set offset and slope of the line
    func6->set_paramsV(-1,1.5);
    func6->set_title("special function: linear");
    plot->addGraph(func6);

This code snippets above result in a plot like this:

Back to JKQTPlotter main page

3.8 KiB Raw Blame History

JKQtPlotter

Plotting Mathematical Functions as Line Graphs

3.8 KiB

Raw Blame History