/// <summary>
  /// Use a OpenFile common dialog to select a datafile and read data points.
  /// The points may be in one of two formats
  ///     1.)  Each line contains two numbers separated by one or more
  ///          spaces or tabs
  ///              The first number is the x-coordinate, the second number 
  ///              is the y-coordinate
  ///     2.)  Each line contains one number
  ///            The numbers are all considered y-coordinates.  
  ///            The x-coordinate is implied by the line number.  
  ///            The x-coordinated of the first line is zero.
  /// The function returns an array of PointF objects.  Each PointF 
  /// contains an X and Y coordinate.
  /// </summary>
    PointF[] readGraphData(out float minX, out float maxX,
                           out float minY, out float maxY)
    {
      // Use a common dialog box to get the file.
      OpenFileDialog dialog = new OpenFileDialog();
      DialogResult dialogResult = dialog.ShowDialog();
      PointF[] dataPoints = new PointF[0];
      minX = 0.0f;
      maxX = 0.0f;
      minY = 0.0f;
      maxY = 0.0f;

      // If the user doesn't click OK, do nothing.
      if (dialogResult == DialogResult.OK)
      {
        // Open the selected file for reading.
        StreamReader reader = new StreamReader(dialog.OpenFile());

        // There can be any number of spaces and/or tabs between x and y
        char[] separators = new char[] { ' ', '\t' };

        // Read each line into nextLine.
        string nextLine;

        // Because we don't know how many points we will read, we read them
        // first into a List and then copy them to an array.
        List<PointF> dataList = new List<PointF>();
        float nextX = 0;

        do
        {
          // Read a single line
          nextLine = reader.ReadLine();

          // If it is a not a null or empty line
          if (!String.IsNullOrEmpty(nextLine))
          {
            // Divide the line into fields
            string[] field = nextLine.Split(separators);

            // If there is only on value per line
            if (field.Length == 1)
            {
              // Use nextX for the x-coordinate and the read-in value for
              // the y-coordinate.
              dataList.Add(new PointF(nextX, Convert.ToSingle(field[0])));
              nextX = nextX + 1.0f;
            }
            else
            {
              // if there is more than one field, use the first two for 
              // x and y respectively.
              dataList.Add(new PointF(Convert.ToSingle(field[0]), 
                                      Convert.ToSingle(field[1])));
            }
          }
        } while (!reader.EndOfStream);

        // Close the file stream.
        reader.Close();

        // If we read at least one point
        if (dataList.Count > 0)
        {
          // Create an array to hold the points
          dataPoints = new PointF[dataList.Count];

          // Copy the list to the array
          int i = 0;
          foreach (PointF point in dataList)
          {
            dataPoints[i] = point;
            ++i;
          }
        }

        // Find the min and max values of x and y
        maxX = dataPoints[0].X;
        minX = dataPoints[0].X;

        maxY = dataPoints[0].Y;
        minY = dataPoints[0].Y;

        foreach (PointF point in dataPoints)
        {
          if (point.X < minX) minX = point.X;
          if (point.X > maxX) maxX = point.X;
          if (point.Y < minY) minY = point.Y;
          if (point.Y > maxY) maxY = point.Y;
        }

      }
      return dataPoints;
    }