def METHOD_NAME(p, X, Y, Z, P, *args):
    """3D PSF model function with constant background - parameter vector [A, x0, y0, z0, background]"""
    A, x0, y0, z0, b = p
    #return A*scipy.exp(-((X-x0)**2 + (Y - y0)**2)/(2*s**2)) + b
    return genWidefieldPSF(X, Y, Z, P,A*1e3, x0, y0, z0, *args) + b