This project (see `./examples/simpletest_parsedfunctionplot/`) demonstrates how to plot mathematical functions as line graphs. The functions are defined as strings that will be evaluated with the equation parser, integrated into JKQTPlotter.
Note: See the example [Plotting Mathematical Functions as Line Graphs](../simpletest_functionplot) if you don't want to draw parsed functions, but want to provide a C function, or C++ functor!
As you can see a graph of the type `JKQTPXParsedFunctionLineGraph` is used, which plots a function that depends on the variable `x`. The given function is parsed and evaluated (see [`lib/jkqtplottertools/jkqtpmathparser.h`](https://github.com/jkriege2/JKQTPlotter/blob/master/lib/jkqtplottertools/jkqtpmathparser.h) for details on the features of the math parser). An intelligent drawing algorithm chooses the number of control points for drawing a smooth graph, with sufficient amount of details, by evaluating locally the slope of the function.
In the example in [`test/simpletest_parsedfunctionplot/simpletest_parsedfunctionplot.cpp`](../simpletest_parsedfunctionplot/simpletest_parsedfunctionplot.cpp) we do not simply set a fixed function, but add a `QLineEdit` which allows to edit the function and redraws it, once ENTER is pressed:
As shown in [Plotting Mathematical Functions as Line Graphs](../simpletest_functionplot) you can also use externally set parameters in a plot function. These parameters can be double numbers and may be set with either as an internal parameter vector, or may be read from a parameter column (as shown in the [linked example](../simpletest_functionplot)). These parameters are available as variables `p1`, `p2`, ... in the function string. Here is a small example:
If you use the graph class `JKQTPYParsedFunctionLineGraph` instead of `JKQTPXParsedFunctionLineGraph`, you can plot functions `x=f(y)` (instead of `y=f(x)`). The function from the example above will then ahve to be changed to `sin(y*8)*exp(-y/4)` and the result will look like this:
The adaptive capabilities of the rendering algorithm can be seen, when plotting e.g. `2/x`, which is drawn smoothely, even around the undefined value at `x=0`:
With an additional checkbox in this example, you can switch drawing the actual sample points of the drawing algorithm on and off, by calling `parsedFunc->set_displaySamplePoints(...)`. This can be used to debug the drawing algorithm and explore its parameters (which you can set with `set_minSamples()`, `set_maxRefinementDegree()`, `set_slopeTolerance()`, `set_minPixelPerSample()`). Here is an example of a 2/x function with shown sample points: