def cyl_to_spher(R,Z, phi):
    """
    NAME:

       cyl_to_spher

    PURPOSE:

       convert from cylindrical to spherical coordinates

    INPUT:

       R, Z, phi- cylindrical coordinates

    OUTPUT:

       R, theta, phi - spherical coordinates

    HISTORY:

       2016-05-16 - Written - Aladdin

    """
    theta = nu.arctan2(R, Z)
    r = (R**2 + Z**2)**.5
    return (r,theta, phi)