def testf(x, y):
    
    """
    Contains the function to be minimized by the stumbledown algorithm.
    
    Parameters:
        x (float): x coordinate
        
        y (float): y coordinate
        
    Returns:
        f (float): value obtained after evaluating the function at the point
        (x, y)
    """
    
    f = (x - 5)**2 + (y - 3)**2 + 17
    
    return f