import math


def EllipseCircum( a, b ):
	"""Calcluates circumference of an ellipse.
	
	Given an ellipse defined by semi-major axis a and semi-minor axis b, 
	the function returns the circumference of the ellipse, using the 
	approximation of Ramanujan.
	
	Parameters
    ----------
    a : float
    	semi-major axis of ellipse
    b : float
    	semi-minor axis of ellipse
    
    Returns
    -------
    circumference : float
    """
	
	return math.pi * ( 3*(a + b) - math.sqrt( (3*a +  b)*(a + 3*b) ) )