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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def alignment_a(self):
 """Computes the rotation matrix that aligns the unit cell with the Cartesian axes, starting with cell vector a. * a parallel to x * b in xy-plane with b_y positive * c with c_z positive """

        from molmod.transformations import Rotation
        new_x = self.matrix[:, 0].copy()
        new_x /= np.linalg.norm(new_x)
        new_z = np.cross(new_x, self.matrix[:, 1])
        new_z /= np.linalg.norm(new_z)
        new_y = np.cross(new_z, new_x)
        new_y /= np.linalg.norm(new_y)
        return Rotation(np.array([new_x, new_y, new_z]))