# 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. 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: 

```.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) .