Error bars are used to indicate the estimated error in a measurement. Errors bars indicate the uncertainty in the x and/or y values.

Vertical Error Bars

The most common error bar plot is one in which the errors are in the y-values. This example shows such an error bar plot. Note that the values of the low and high arguments are absolute y-values, not relative or percentage values.

 

(Download Code)

 

using Imsl.Chart2D;

using System.Drawing;

using Imsl.Stat;

 

public class SampleErrorBar : FrameChart {

 

    public SampleErrorBar() {

        Random r = new Random(123457);

 

        Chart chart = this.Chart;

        AxisXY axis = new AxisXY(chart);

 

        // Generate a random data set, with random errors

        int n = 20;

        double[] x = new double[n];

        double[] y = new double[n];

        double[] low = new double[n];

        double[] high = new double[n];

        for (int k = 0;  k < n;  k++) {

            x[k] = k + 1;

            y[k] = r.NextDouble();

            low[k] = y[k] - 0.25*r.NextDouble();

            high[k] = y[k] + 0.25*r.NextDouble();

        }

 

        ErrorBar data = new ErrorBar(axis, x, y, low, high);

        data.DataType = ErrorBar.DATA_TYPE_ERROR_Y |

            Data.DATA_TYPE_MARKER;

        data.MarkerType = Data.MARKER_TYPE_FILLED_CIRCLE;

        data.MarkerColor = Color.Red;

    }

 

    public static void Main(string[] argv) {

        System.Windows.Forms.Application.Run(new SampleErrorBar());

    }

}

 

 

Horizontal Error Bars

It is also possible to have horizontal error bars, indicating errors in x, as shown in this example.

 

(Download Code)

 

using Imsl.Chart2D;

using System.Drawing;

using Imsl.Stat;

 

public class SampleHorizontalErrorBar : FrameChart {

 

    public SampleHorizontalErrorBar() {

        Random r = new Random(123457);

 

        Chart chart = this.Chart;

        AxisXY axis = new AxisXY(chart);

 

        // Generate a random data set, with random errors

        int n = 20;

        double[] x = new double[n];

        double[] y = new double[n];

        double[] low = new double[n];

        double[] high = new double[n];

        for (int k = 0;  k < n;  k++) {

            x[k] = k;

            y[k] = r.NextDouble();

            low[k] = x[k] - 5.0*r.NextDouble();

            high[k] = x[k] + 5.0*r.NextDouble();

        }

 

        ErrorBar data = new ErrorBar(axis, x, y, low, high);

        data.DataType = ErrorBar.DATA_TYPE_ERROR_X |

            Data.DATA_TYPE_MARKER;

        data.MarkerType = Data.MARKER_TYPE_FILLED_CIRCLE;

        data.MarkerColor = Color.Red;

    }

 

    public static void Main(string[] argv) {

        System.Windows.Forms.Application.Run(

            new SampleHorizontalErrorBar());

    }

}

 

Mixed Error Bars

To show errors in both x and y, it is necessary to create both vertical and horizontal error bar objects. This example shows such a chart.

(Download Code)

 

using Imsl.Chart2D;

using System.Drawing;

using Imsl.Stat;

 

public class SampleMixedErrorBar : FrameChart {

 

    public SampleMixedErrorBar() {

        Random r = new Random(123457);

 

        Chart chart = this.Chart;

        AxisXY axis = new AxisXY(chart);

 

        // Generate a random data set, with random errors

        int n = 20;

        double[] x = new double[n];

        double[] y = new double[n];

        double[] xlow = new double[n];

        double[] xhigh = new double[n];

        double[] ylow = new double[n];

        double[] yhigh = new double[n];

        for (int k = 0;  k < n;  k++) {

            x[k] = k;

            y[k] = r.NextDouble();

            xlow[k] = x[k] - r.NextDouble();

            xhigh[k] = x[k] + r.NextDouble();

            ylow[k] = y[k] - 0.25*r.NextDouble();

            yhigh[k] = y[k] + 0.25*r.NextDouble();

        }

 

        ErrorBar dataY = new ErrorBar(axis, x, y, ylow, yhigh);

        dataY.DataType = ErrorBar.DATA_TYPE_ERROR_Y | Data.DATA_TYPE_MARKER;

        dataY.MarkerType = Data.MARKER_TYPE_FILLED_CIRCLE;

        dataY.MarkerColor = Color.Red;

 

        ErrorBar dataX = new ErrorBar(axis, x, y, xlow, xhigh);

        dataX.DataType = ErrorBar.DATA_TYPE_ERROR_X;

        dataX.MarkerType = Data.MARKER_TYPE_FILLED_CIRCLE;

        dataX.MarkerColor = Color.Red;

    }

 

    public static void Main(string[] argv) {

        System.Windows.Forms.Application.Run(new SampleMixedErrorBar());

    }

}

 

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