def peak_background_bias(nu):
    """
    Returns the Lagrangian biases, (b1,b2), given nu.
    This is helpful if we want to make our basis set f, nu.
    """
    delc = 1.686
    a    = 0.707
    p    = 0.30
    anu2 = a*nu**2
    b1   = (anu2-1+2*p/(1+anu2**p))/delc
    b2   = (anu2**2-3*anu2+2*p*(2*anu2+2*p-1)/(1+anu2**p))/delc**2
    return( (b1,b2) )
    #