import math


def blend2(d=0.0, u=1.0, s=5.0):
    """
       blending function gaussian
       d = delta x = xabs - xdr
       u = uncertainty radius of xabs estimate error
       s = tuning scale factor

       returns blend
    """
    d = float(d)
    u = float(u)
    s = float(abs(s)) # make sure positive

    b = 1.0 - math.exp( - s * (d * d)/(u * u))

    return b