def tnext_beta(t, beta=0.5):
    """ Simple function, as used in MEGA: ``upper_tnext(t)`` = :math:`t^{\\beta}`. Default to :math:`t^{0.5}`.

    >>> tnext_beta(100, beta=0.1)  # doctest: +ELLIPSIS
    1.584...
    >>> tnext_beta(100, beta=0.5)
    10.0
    >>> tnext_beta(100, beta=0.9)  # doctest: +ELLIPSIS
    63.095...
    >>> tnext_beta(1000)  # doctest: +ELLIPSIS
    31.622...
    """
    return t ** beta
