def norm_coefficient(m, n):
    'Calculate normalizaiton coeficient of each zernikes; Rn+-m(1) = 1 for\n    all n, m. THhe folowing euqtion is used (eq. 4 in [1]):\n\n    :math:`N_{n}^{m}=\\left(\x0crac{2(n+1)}{1+\\delta_{m 0}}\right)^{1 / 2}`\n\n    :param m: zernike m-degree, angular frequency\n    :type m: int\n    :param n: zernike n-degree, radial order\n    :type n: int\n    :return: calculate normalization coefficient\n    :rtype: float\n\n    **Example**\n\n    >>> import pyoptica as po\n    >>>\n    >>> m, n = 1, 3\n    >>> po.zernikes.norm_coefficient(m, n)\n    >>> 2.8284271247461903\n\n    **References**\n\n    [1] Vasudevan Lakshminarayanan and Andre Fleck (2011) -\n    *Zernike polynomials: a guide*, Journal of Modern Optics\n\n    '
    numerator = 2 * (n + 1)
    denominator = 2 if m == 0 else 1
    norm = (numerator / denominator) ** 0.5
    return norm
