JMSL Chart Programmer's Guide

Charting 2D Types >> Function Plot

Function Plot

A function plot shows the value of a function f(x) over an interval [a,b]. The function must be defined as an implementation of the ChartFunction interface. A Data node constructor creates a line chart from the function. The look of the function is controlled by the line attributes.

The ChartFunction interface requires that the function name be "f", that the function has a single double argument and that it returns a double.

Example

This example plots the sinc function on the interval [-10,10]. The sinc function is defined to be sin(px)/px. In this example, sinc is an anonymous inner class that implements ChartFunction. This is required by the function Data constructor. In the code, the case x=0 is handled specially to avoid returning NaN.

import com.imsl.chart.*;
import java.awt.Color;

public class SampleFunction extends JFrameChart {

    public SampleFunction() {        
        Chart chart = getChart();
        AxisXY axis = new AxisXY(chart);
  
        ChartFunction sinc = new ChartFunction() {
            public double f(double x) {
                if (x == 0.0) return 1.0;
                return Math.sin(Math.PI*x) / (Math.PI*x);
            }
        };
        Data data = new Data(axis, sinc, -10.0, 10.0);
        data.setLineColor(Color.blue);
    }
    
    public static void main(String argv[]) {
        new SampleFunction().setVisible(true);
    }
}

Histogram Example

For another example of a ChartFunction, see Histogram.

Spline Chart

This example shows raw data points, as markers, and their fit to a shape preserving spline. The spline is computed using CsShape found in the JMSL Math package (which extends Spline). The ChartSpline class wraps the Spline into a ChartFunction. This example also enables the Legend.

import com.imsl.chart.*;
import com.imsl.math.CsShape;
import java.awt.Color;

public class SampleSpline extends JFrameChart {

    public SampleSpline() {
        try {
            Chart chart = getChart();
            AxisXY axis = new AxisXY(chart);
            chart.getLegend().setPaint(true);
            
            double x[] = {0, 1, 2, 3, 4, 5, 8, 9, 10};
            double y[] = {1.0, 0.8, 2.4, 3.1, 4.5, 5.8, 6.2, 4.9, 3.7};
            Data dataMarker = new Data(axis, x, y);
            dataMarker.setTitle("Data");
            dataMarker.setDataType(Data.DATA_TYPE_MARKER);
            dataMarker.setMarkerType(Data.MARKER_TYPE_FILLED_CIRCLE);
            
            CsShape spline = new CsShape(x, y);
            Data dataSpline = new Data(axis, new ChartSpline(spline), 0., 10.);
            dataSpline.setTitle("Fit");
            dataSpline.setLineColor(Color.blue);
        } catch (com.imsl.IMSLException e) {
            e.printStackTrace();
        }
    }
    
    public static void main(String argv[]) {
        new SampleSpline().setVisible(true);
    }
}

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