TrendFunction: YValues set to XValues

[Trimble Terrasat]

Hello,

I have code as follows:

Code: Select all

Line line = new Line();
line.DataSource = lineTemp;

TrendFunction trend = new TrendFunction();
trend.PeriodAlign = PeriodAligns.Center;
trend.PeriodStyle = PeriodStyles.NumPoints;
trend.Period = line.Count;
line.Function = trend;

Sometimes, especially if the number of points in the line is quite small, the XValues are written into the YValues instead of calculating the YValues via the trend function. For us this seems to be a bug. Do you know more about this?

Kind regards

Jens

[Narcís]

Hi Jens,

I'm not able to reproduce the problem here using code snippet below. Could you please modify it so that we can reproduce the problem here and let us know the TeeChart version you are using?

Code: Select all

    public Form1()
    {
      InitializeComponent();
      InitializeChart();
    }

    private void InitializeChart()
    {
      Steema.TeeChart.Styles.Line lineTemp = new Steema.TeeChart.Styles.Line(tChart1.Chart);
      lineTemp.FillSampleValues(5);

      Steema.TeeChart.Styles.Line line = new Steema.TeeChart.Styles.Line(tChart1.Chart);
      line.DataSource = lineTemp;

      Steema.TeeChart.Functions.TrendFunction trend = new Steema.TeeChart.Functions.TrendFunction();
      trend.PeriodAlign = Steema.TeeChart.Functions.PeriodAligns.Center;
      trend.PeriodStyle = Steema.TeeChart.Functions.PeriodStyles.NumPoints;
      trend.Period = line.Count;
      line.Function = trend;
    }

Thanks in advance.

[Trimble Terrasat]

Hi Narcís,

with the following code I can reproduce:

Code: Select all

public Form1()
{
	InitializeComponent();
	InitializeChart();
}

private void InitializeChart()
{
	Steema.TeeChart.Styles.Line lineTemp = new 
                    Steema.TeeChart.Styles.Line( tChart1.Chart );
	lineTemp.Add( 924266611, 1.1 );
	lineTemp.Add( 924266612, 1.2 );
	lineTemp.Add( 924266613, 1.3 );
	lineTemp.Add( 924266614, 1.4 );
	lineTemp.Add( 924266615, 1.5 );

	Steema.TeeChart.Styles.Line line = new 
                    Steema.TeeChart.Styles.Line( tChart1.Chart );
	line.DataSource = lineTemp;

	Steema.TeeChart.Functions.TrendFunction trend = new 
                    Steema.TeeChart.Functions.TrendFunction();
	trend.PeriodAlign = 
                    Steema.TeeChart.Functions.PeriodAligns.Center;
	trend.PeriodStyle = 
                    Steema.TeeChart.Functions.PeriodStyles.NumPoints;
	trend.Period = line.Count;
	line.Function = trend;
}

The problem seems to occur with large x values. There seems to be no internal reduction of the x values for the trend calculation.


Regards

Jens

[Trimble Terrasat]

Sorry, I forgot: We have here Version 2.0.2652.22325.

But the problem also occured with the latest evaluation version.

[Narcís]

Hi Jens,

Thanks for the information. I've been able to reproduce the issue here and added it (TF02014096) to the bug list to be fixed for future releases.

[Christopher]

Hi Jens,

This is an interesting problem :-)

This code works as expected:

Code: Select all

    private void InitializeChart()
    {
      tChart1.Aspect.View3D = false;
      Steema.TeeChart.Styles.Line lineTemp = new
      Steema.TeeChart.Styles.Line(tChart1.Chart);

      lineTemp.Add(10000001, 0.1);
      lineTemp.Add(10000002, 0.2);
      lineTemp.Add(10000003, 0.3);
      lineTemp.Add(10000004, 0.4);
      lineTemp.Add(10000005, 0.5);

      Steema.TeeChart.Styles.Line line = new Steema.TeeChart.Styles.Line(tChart1.Chart);
      line.DataSource = lineTemp;

      Steema.TeeChart.Functions.TrendFunction trend = new Steema.TeeChart.Functions.TrendFunction();
      trend.PeriodAlign = Steema.TeeChart.Functions.PeriodAligns.Center;
      trend.PeriodStyle = Steema.TeeChart.Functions.PeriodStyles.NumPoints;
      trend.Period = line.Count;
      line.Function = trend;
    }

Now, adding in another significant digit to the XValues causes an incorrect chart, e.g.

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      lineTemp.Add(100000001, 0.1);
      lineTemp.Add(100000002, 0.2);
      lineTemp.Add(100000003, 0.3);
      lineTemp.Add(100000004, 0.4);
      lineTemp.Add(100000005, 0.5);

The two lines should coincide, but don't. Adding another significant digit to the XValues causes the chart you showed to us.

The issue here is that the size of the input values causes the internal algorithms to work at a precision beyond that of the System.Double type. The line of code that causes the issue is this one:

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divisor = count*sumX2-sumX*sumX;

here, sumX is the sum of all the XValues, sumX2 is the sum of all the squares of the XValues and count is the number of values in the series. So, feeding the values into this from the chart which gives us the "incorrect" values, we have:

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    private void InitializeOther()
    {
      double divisor, sumX2, sumX;
      int count;

      sumX2 = 5.00000003E+18;
      sumX = 5000000015.0;
      count = 5;

      divisor = count * sumX2 - sumX * sumX;
      MessageBox.Show(divisor.ToString());
    }

this calculation gives us zero, which is why the chart displays as it does. Now, one way round this problem would be to use decimals instead of doubles to perform the calculation, however, the decimal type has a low range (±1.0 x 10-28 to ±7.9 x 10+28) and the numbers we use above are already in the area of 10+20. Using decimals would therefore resolve the issue for the specific case in hand, but adding a couple more significant digits would cause the algorithm to reach the limit of decimal's range. We therefore don't see the use of decimals as a viable alternative here.

Our best suggestion, therefore, is that you factor down the input doubles to a range which causes a precise calculation. This can be done using code similar to the following:

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    private double factor = 0.01;

    private void InitializeChart()
    {
      tChart1.Aspect.View3D = false;
      tChart1.GetAxisLabel += new GetAxisLabelEventHandler(tChart1_GetAxisLabel);
      Steema.TeeChart.Styles.Line lineTemp = new
      Steema.TeeChart.Styles.Line(tChart1.Chart);

      lineTemp.Add(1000000001 * factor, 0.1);
      lineTemp.Add(1000000002 * factor, 0.2);
      lineTemp.Add(1000000003 * factor, 0.3);
      lineTemp.Add(1000000004 * factor, 0.4);
      lineTemp.Add(1000000005 * factor, 0.5);

      Steema.TeeChart.Styles.Line line = new Steema.TeeChart.Styles.Line(tChart1.Chart);
      line.DataSource = lineTemp;

      Steema.TeeChart.Functions.TrendFunction trend = new Steema.TeeChart.Functions.TrendFunction();
      trend.PeriodAlign = Steema.TeeChart.Functions.PeriodAligns.Center;
      trend.PeriodStyle = Steema.TeeChart.Functions.PeriodStyles.NumPoints;
      trend.Period = line.Count;
      line.Function = trend;
    }

    void tChart1_GetAxisLabel(object sender, GetAxisLabelEventArgs e)
    {
      if (sender == tChart1.Axes.Bottom)
      {
        string text = e.LabelText;
        double d = double.Parse(text);
        d *= 1 / factor;
        e.LabelText = d.ToString(tChart1.Axes.Bottom.Labels.ValueFormat);
      }
    }

[Trimble Terrasat]

Hi Christopher,

thank you very much for your reply.

For our task decimal values would solve the problem. Our values probably won't be larger than 10+22.
So I request if you can fix the bug by implementing the class with decimal variables. A solution by the mid of the year would be no problem.

For us this would be more appropriate than a solution with factors.

Best regards

Jens

[Narcís]

Hi Jens,

Ok, I have added your request to the wish-list to be considered for inclusion in future releases.

[Christopher]

Jens,

Ok, we've now implemented a new "UseDecimals" property (default false) into the base class of the TrendFuncion which enables code like that in the example below to run and produce a perfectly accurate chart:

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    private void InitializeChart()
    {
      tChart1.Aspect.View3D = false;
      Steema.TeeChart.Styles.Line lineTemp = new
      Steema.TeeChart.Styles.Line(tChart1.Chart);

      lineTemp.Add(10000000000001, 0.1);
      lineTemp.Add(10000000000002, 0.2);
      lineTemp.Add(10000000000003, 0.3);
      lineTemp.Add(10000000000004, 0.4);
      lineTemp.Add(10000000000005, 0.5); 

      Steema.TeeChart.Styles.Line line = new Steema.TeeChart.Styles.Line(tChart1.Chart);
      line.DataSource = lineTemp;

      Steema.TeeChart.Functions.TrendFunction trend = new Steema.TeeChart.Functions.TrendFunction();
      trend.UseDecimals = true;
      trend.PeriodAlign = Steema.TeeChart.Functions.PeriodAligns.Center;
      trend.PeriodStyle = Steema.TeeChart.Functions.PeriodStyles.NumPoints;
      trend.Period = line.Count;
      line.Function = trend;
    }

This new property will be in the next version 3 maintenance release, due to be made public in the near future.