test cholesky_solve_and_invert and then fall back to slower but more robust solver np.linalg.lstsq , np.linalg.pinv if linalg exception raised
test cholesky_solve_and_invert and then fall back to slower but more robust solver np.linalg.lstsq , np.linalg.pinv if linalg exception raised

desihub/desispec,desihub/desispec