def METHOD_NAME(gam_init, prob):
    """
    Uses complex step to compute gradient of range wrt initial angle.
    Parameters
    ----------
    gam_init : float
        Initial cannonball firing angle in degrees.
    prob : <Problem>
        OpenMDAO problem that contains the equations of motion.
    Returns
    -------
    float
        Derivative of range wrt initial angle in m/deg.
    """
    step = 1.0e-14
    dr_dgam = eval_cannonball_range(gam_init + step * 1j, prob, complex_step=True)
    return dr_dgam.imag / step