# Example (JKQTPlotter): Plotting Parametric Mathematical Curves as Line Graphs                                      {#JKQTPlotterEvalCurves}


## Basics
This project (see `./examples/evalcurve/`) demonstrates how to plot mathematical functions as line graphs with `JKQTPXYFunctionLineGraph`. 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. 

If you want to evaluate the parametric function explicitly, you can use `JKQTPXYLineGraph` or `JKQTPXYParametrizedScatterGraph` and have a look at the example [`./examples/parametriccurve`](https://github.com/jkriege2/JKQtPlotter/tree/master/examples/parametriccurve).

[TOC]

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

```.cpp
    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](https://en.wikipedia.org/wiki/Butterfly_curve_(transcendental)), 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 

```.cpp
    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 `t`and a vector of parameters. Here is an example:

```.cpp
    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 

```.cpp
    // 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:

```.cpp
    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:

![evalcurve](https://raw.githubusercontent.com/jkriege2/JKQtPlotter/master/screenshots/evalcurve.png)

# Notes

This example describes how to draw 2D parametric curves. For (simpler) 1D-functions f(x) or f(y), see [examples/functionplot](https://github.com/jkriege2/JKQtPlotter/tree/master/examples/functionplot) .


