'Calculates the semi-latus rectum of the Ellipse.
Semi-latus rectum is defined as one half of the the chord through a
focus parallel to the conic section directrix of a conic section.
Returns
semilatus_rectum : number
See Also
apoapsis : Returns greatest distance between focus and contour
periapsis : The shortest distance between the focus and the contour
Examples
>>> from sympy import Point, Ellipse
>>> p1 = Point(0, 0)
>>> e1 = Ellipse(p1, 3, 1)
>>> e1.semilatus_rectum
1/3
References
[1] http://mathworld.wolfram.com/SemilatusRectum.html
[2] https://en.wikipedia.org/wiki/Ellipse#Semi-latus_rectum'

@property
def semilatus_rectum(self):

    return (self.major * (1 - (self.eccentricity ** 2)))
