JKQtPlotter/examples/evalcurve

Example (JKQTPlotter): Plotting Parametric Mathematical Curves as Line Graphs

Basics

This project (see ./examples/evalcurve/) demonstrates how to plot mathematical functions as line graphs. The functions may be defined as static C functions, C++ functors or c++ inline functions. The functions may simply depend on the parameter t, or on t and a vector of parameters.

The class uses an adaptive algorithm, which determines by the local slope, at how many points (or how close points) the functor has to be evaluated.

[TOC]

Simple C++ inline function

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

    JKQTPXYFunctionLineGraph* func1=new JKQTPXYFunctionLineGraph(plot);
    func1->setPlotFunctionFunctor([](double t) ->QPointF {
        return QPointF(
              sin(t)*(exp(cos(t))-2.0*cos(4.0*t)-jkqtp_pow5(sin(t/12.0))),
              cos(t)*(exp(cos(t))-2.0*cos(4.0*t)-jkqtp_pow5(sin(t/12.0)))
            );
    });
    func1->setTRange(0, 12.0*JKQTPSTATISTICS_PI);
    func1->setTitle("C++-inline function: \"Butterfly Curve\"");
    plot->addGraph(func1);

Note that here a functor is defined, which calculates the points on a Butterfly Curve, i.e. a function mapping a parameter t to a two-dimensional point QPointF with complex functions for x and y. This function is evaluated on a range of values for t, set by

    func1->setTRange(0, 2.0*JKQTPSTATISTICS_PI);

Simple C++ inline function with Parameters

JKQTPXYFunctionLineGraph allows to use more complex functors alternatively: These depend on the variable tand a vector of parameters. Here is an example:

    func2->setPlotFunctionFunctor([](double t, const QVector<double>& params) ->QPointF {
        return QPointF(
              3.0*sin(params[0]*t+params[2])+8.0,
              3.0*sin(params[1]*t)
            );
    });
    // now we define the 3 parameters of the function
    func2->setParamsV(5, 4, JKQTPSTATISTICS_PI/4.0);
    // and define the range over which to evaluate
    func2->setTRange(0, 2.0*JKQTPSTATISTICS_PI);
    func1->setTitle("C++-inline function $[ sin(5{\\cdot}t+\\pi/4), sin(4{\\cdot}t) ]$");
    plot->addGraph(func1);

In the functor we can use the entries in the vector param as function parameters. The values in this vector are defined by

    // now we define the 3 parameters of the function
    func2->setParamsV(5, 4, JKQTPSTATISTICS_PI/4.0);

Alternatively they can also be taken from a column in the internal datastore. Then you have to call:

    func2->setParameterColumn(ColumnID);

instead, where ColumnID is the ID of the column with the parameter values.

Screenshot

This code snippets above result in a plot like this:

Notes

This example describes how to draw 2D parametric curves. For (simpler) 1D-functions f(x) or f(y), see examples/functionplot .