This function is called internally from the graphical functions caellipse and nscaellipse.
It constructs the algebraic ellipses of confidence.
The length of the horizontal ellipse semi-axis.
The length of the vertical ellipse semi-axis.
The coordinate of the generic point on the horizontal axis.
The coordinate of the generic point on the vertical axis.
The color of ellipses.
Beh EJ and Lombardo R 2014 Correspondence Analysis: Theory, Practice and New Strategies. John Wiley & Sons. Macdonald PDM 2002 Drawing an ellipse in Splus or R. Available at www.math.mcmaster.ca/peter/s4m03/s4m03_0102/ellipse.html (accessed August 18, 2016).