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77 lines
3.4 KiB
Markdown
77 lines
3.4 KiB
Markdown
# Example (JKQTPlotter): Plotting Parametric Mathematical Curves as Line Graphs {#JKQTPlotterEvalCurves}
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## Basics
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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.
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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.
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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).
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[TOC]
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# Simple C++ inline function
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The example shows how to plot a simple C++ inline function:
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```.cpp
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JKQTPXYFunctionLineGraph* func1=new JKQTPXYFunctionLineGraph(plot);
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func1->setPlotFunctionFunctor([](double t) ->QPointF {
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return QPointF(
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sin(t)*(exp(cos(t))-2.0*cos(4.0*t)-jkqtp_pow5(sin(t/12.0))),
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cos(t)*(exp(cos(t))-2.0*cos(4.0*t)-jkqtp_pow5(sin(t/12.0)))
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);
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});
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func1->setTRange(0, 12.0*JKQTPSTATISTICS_PI);
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func1->setTitle("C++-inline function: \"Butterfly Curve\"");
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plot->addGraph(func1);
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```
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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
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```.cpp
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func1->setTRange(0, 2.0*JKQTPSTATISTICS_PI);
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```
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# Simple C++ inline function with Parameters
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`JKQTPXYFunctionLineGraph` allows to use more complex functors alternatively: These depend on the variable `t`and a vector of parameters. Here is an example:
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```.cpp
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func2->setPlotFunctionFunctor([](double t, const QVector<double>& params) ->QPointF {
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return QPointF(
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3.0*sin(params[0]*t+params[2])+8.0,
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3.0*sin(params[1]*t)
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);
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});
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// now we define the 3 parameters of the function
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func2->setParamsV(5, 4, JKQTPSTATISTICS_PI/4.0);
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// and define the range over which to evaluate
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func2->setTRange(0, 2.0*JKQTPSTATISTICS_PI);
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func1->setTitle("C++-inline function $[ sin(5{\\cdot}t+\\pi/4), sin(4{\\cdot}t) ]$");
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plot->addGraph(func1);
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```
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In the functor we can use the entries in the vector `param` as function parameters. The values in this vector are defined by
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```.cpp
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// now we define the 3 parameters of the function
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func2->setParamsV(5, 4, JKQTPSTATISTICS_PI/4.0);
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```
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Alternatively they can also be taken from a column in the internal datastore. Then you have to call:
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```.cpp
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func2->setParameterColumn(ColumnID);
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```
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instead, where `ColumnID` is the ID of the column with the parameter values.
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# Screenshot
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This code snippets above result in a plot like this:
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# Notes
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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) .
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