getZernike

        Retrieve a map representing the index-th Zernike polynomial

        Args:
            index (int): The index of Zernike map to be generated,
                following Noll 1976 ordering.

        Returns:
            np.array: A map representing the index-th Zernike polynomial

def getZernike(self, index):
        """getZernike

        Retrieve a map representing the index-th Zernike polynomial

        Args:
            index (int): The index of Zernike map to be generated,
                following Noll 1976 ordering.

        Returns:
            np.array: A map representing the index-th Zernike polynomial

        """
        if index not in list(self._dictCache.keys()):
            self._dictCache[index]= self._polar(index, self._rhoMap,
                                                self._thetaMap)
        return self._dictCache[index]