class Magick::RVG::Ellipse

def initialize(rx, ry, cx=0, cy=0)

Use the RVG::ShapeConstructors#ellipse method to create Ellipse objects in a container.
and a vertical radius +ry+.
Define an ellipse with a center at [cx, cy], a horizontal radius +rx+ 
def initialize(rx, ry, cx=0, cy=0)
    super()
    rx, ry, cx, cy = Magick::RVG.convert_to_float(rx, ry, cx, cy)
    if rx < 0 || ry < 0
        raise ArgumentError, "radii must be >= 0 (#{rx}, #{ry} given)"
    end
    @primitive = :ellipse
    # Ellipses are always complete.
    @args = [cx, cy, rx, ry, 0, 360]
end