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107 lines
5.9 KiB
Markdown
107 lines
5.9 KiB
Markdown
# Example (JKQTPlotter): Line Graph with Logarithmic y-axis {#JKQTPlotterLogAxes}
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This project (see `./examples/logaxes/`) simply creates a JKQTPlotter widget (as a new window) and several line-graphs of different resonance curves.
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The source code of the main application can be found in [`logaxes.cpp`](https://github.com/jkriege2/JKQtPlotter/tree/master/examples/logaxes/logaxes.cpp). Mainly several graphs are generated in a loop and then different line styles are applied to the graphs (set by ``graph->setLineStyle()`). The colors are set automtically from an internal default palette. The main loop looks like this:
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```.cpp
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QVector<Qt::PenStyle> pens {Qt::SolidLine, Qt::DashLine, Qt::DotLine, Qt::DashDotLine, Qt::DashDotDotLine };
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for (int id=0; id<D.size(); id++) {
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// generate some plot data
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QVector<double> Y;
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for (auto& xx: X) {
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Y<<1.0/sqrt(sqr(1-sqr(xx))+sqr(2*xx*D[id]));
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}
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JKQTPXYLineGraph* graph=new JKQTPXYLineGraph(&plot);
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// copy data into datastore and immediately set the yColumn
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graph->setXColumn(columnX);
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graph->setYColumn(ds->addCopiedColumn(Y, "y"+QString::number(id)));
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// don't use symbols
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graph->setSymbolType(JKQTPNoSymbol);
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// use one of different pens
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graph->setLineStyle(pens[id%pens.size()]);
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// set width of graph line
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graph->setLineWidth(1.5);
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// graph title is made from symbol+penstyle
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graph->setTitle(QString("D=\\delta/\\omega_0=%1").arg(D[id]));
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// add the graph to the plot, so it is actually displayed
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plot.addGraph(graph);
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}
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```
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Then a `JKQTPGeoText` is added to the graph, which shows the function plotted in the plot:
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```.cpp
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// 4. Also we add a text-element in the plot to show the plotted function
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// This element (JKQTPGeoText) is taken from the set of geometric elements
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// and is simply parametrized by a position (1.25/10) and the text to display.
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// In addition you can also set the font size (here to 15)
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// Use '$...$' around the actual math string to ensure rendering with a math font
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// (the internal renderer uses XITS fonts by default, which are free and auto-distributed
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// and loaded in the library). If you don't use the math-mode modifiers, the default
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// font of the other rendering text is used, which might not be suitable for
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// high-quality math rendering.
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plot.addGraph(new JKQTPGeoText(&plot, 1.25, 10, "$\\frac{A}{A_{stat}}=\\frac{1}{\\sqrt{\\left(1-\\eta^2\\right)^2+\\left(2{\\eta}D\\right)^2}}$", 15, QColor("black")));
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```
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The difference between not using and using `$...$` for the equation can be seen here:
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- no $-math-mode: 
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- using $-math-mode: 
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Finally the y-axis is switched to logarithmic scaling and the axis labels are set:
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```.cpp
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// 5. set y-axis to logarithmic (x-axis would be analogous, but using `plot.getXAxis()`)
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plot.getYAxis()->setLogAxis(true);
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// now we set the number of label ticks to 9 (you give the count if minor between two majors,
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// so if you want ticks for 1,2,3,...,10,20,30,...,100... you need to use 9:
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plot.getYAxis()->setMinorTicks(9);
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// the minor grid is not shown by default. You can switch it on:
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plot.getYAxis()->setDrawMinorGrid(true);
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// usually axis ticks are shown as numbers 0.01, 0.1, 1, 10, ... You can also force the scientific
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// power-of-10 notation, using:
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plot.getYAxis()->setLabelType(JKQTPCALTexponent);
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// the number of digits in JKQTPCALTexponent determines which labels are drawn in standard-notation,
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// as compared to power-notation (e.g. if set to 1, the labels 0.1=10^{-1}, 1, 10 are shown in
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// standard notation, the rest in power-notation. This tweak improves readability)
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plot.getYAxis()->setLabelDigits(0);
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// minor tick labels are usually not displayed, but you can switch them on, using
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//plot.getYAxis()->setMinorTickLabelsEnabled(true);
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// the axis font sizes can be set with:
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plot.getYAxis()->setTickLabelFontSize(10); // axis tick labels
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plot.getYAxis()->setMinorTickLabelFontSize(7); // minor axis tick labels
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plot.getYAxis()->setLabelFontSize(14); // axis label size
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plot.getXAxis()->setTickLabelFontSize(10); // axis tick labels
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plot.getXAxis()->setMinorTickLabelFontSize(7); // minor axis tick labels
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plot.getXAxis()->setLabelFontSize(14); // axis label size
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// ... and finally set axis labels (using LaTeX notation and $...$ to improve rendering)
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plot.getYAxis()->setAxisLabel("Amplitude $A/A_{stat}$");
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plot.getXAxis()->setAxisLabel("relative driving frequency $\\eta=\\omega/\\omega_0$");
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```
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As an alternative `JKQTPCALTexponentCharacter` does not use the power-of-10 notation, but uses the usual unit-characters, e.g. 0.001=1m, 0.000001=1µ, 10000=10k, ...
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The result looks like this:
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Without the logarithmic scaling we would have:
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Switching the minor grid off results in a plot like this:
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These examples show the results for different typical values for `setMinorTicks()`:
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These examples show the results for different typical values for `setLabelType()`:
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