Helper function that determines maximum number of b vectors for
        each direction.

        This algorithm is adapted from WaveTrans (see Class docstring). There
        should be no reason for this function to be called outside of
        initialization.

def _generate_nbmax(self):
        """
        Helper function that determines maximum number of b vectors for
        each direction.

        This algorithm is adapted from WaveTrans (see Class docstring). There
        should be no reason for this function to be called outside of
        initialization.
        """
        bmag = np.linalg.norm(self.b, axis=1)
        b = self.b

        # calculate maximum integers in each direction for G
        phi12 = np.arccos(np.dot(b[0, :], b[1, :]) / (bmag[0] * bmag[1]))
        sphi123 = np.dot(b[2, :], np.cross(b[0, :], b[1, :])) / \
                  (bmag[2] * np.linalg.norm(np.cross(b[0, :], b[1, :])))
        nbmaxA = np.sqrt(self.encut * self._C) / bmag
        nbmaxA[0] /= np.abs(np.sin(phi12))
        nbmaxA[1] /= np.abs(np.sin(phi12))
        nbmaxA[2] /= np.abs(sphi123)
        nbmaxA += 1

        phi13 = np.arccos(np.dot(b[0, :], b[2, :]) / (bmag[0] * bmag[2]))
        sphi123 = np.dot(b[1, :], np.cross(b[0, :], b[2, :])) / \
                  (bmag[1] * np.linalg.norm(np.cross(b[0, :], b[2, :])))
        nbmaxB = np.sqrt(self.encut * self._C) / bmag
        nbmaxB[0] /= np.abs(np.sin(phi13))
        nbmaxB[1] /= np.abs(sphi123)
        nbmaxB[2] /= np.abs(np.sin(phi13))
        nbmaxB += 1

        phi23 = np.arccos(np.dot(b[1, :], b[2, :]) / (bmag[1] * bmag[2]))
        sphi123 = np.dot(b[0, :], np.cross(b[1, :], b[2, :])) / \
                  (bmag[0] * np.linalg.norm(np.cross(b[1, :], b[2, :])))
        nbmaxC = np.sqrt(self.encut * self._C) / bmag
        nbmaxC[0] /= np.abs(sphi123)
        nbmaxC[1] /= np.abs(np.sin(phi23))
        nbmaxC[2] /= np.abs(np.sin(phi23))
        nbmaxC += 1

        self._nbmax = np.max([nbmaxA, nbmaxB, nbmaxC], axis=0) \
            .astype(np.int)