def __add__(self, b):
        """
        d/dx(a+b) = d/dx(a) + d/dx(b)
        """
        a = self
        if not isinstance(a, AdFloat):
            a = AdFloat(a, 0)
        if not isinstance(b, AdFloat):
            b = AdFloat(b, 0)
        return AdFloat(a.x+b.x, a.dx + b.dx)
def __add__ ( self , b ) : a = self if not isinstance ( a , AdFloat ) : a = AdFloat ( a , 0 ) if not isinstance ( b , AdFloat ) : b = AdFloat ( b , 0 ) return AdFloat ( a . x + b . x , a . dx + b . dx )
d/dx(a+b) = d/dx(a) + d/dx(b)