where and the inverse covariance matrix The fourth set of observational data is 12 Hubble evolution data from [21] and [22], its χ 2 H is defined as Note that redshifts of these data fall in the region z ∈ (0 , 1 . 75). In summary, At first, we divide the whole region of redshift into 4 bins (i.e., m = 3), the divided points and boundaries are (0 , z$_{1}$, z$_{2}$, 1 . 8 , ∞ ), where z$_{1}$ and z$_{2}$ are left as free parameters of the model, and 0 < z$_{1}$ < z$_{2}$ < 1 . 8. In the fourth bin we set w$_{L}$ = − 1. It means that we divide the region with z ∈ (0 , 1 . 8) into 3 bins and seek for two possible turning points of w$_{de}$ ( z ) in this region. The reconstructed w$_{de}$ of the best-fitted model is shown in Fig. 1, X =    l$_{a}$ − 302 . 1 R − 1 . 71 z$_{∗}$ − 1090 . 04    (23) C − 1 M =    1 . 8 27 . 968 − 1 . 103 27 . 968 5667 . 577 − 92 . 263 − 1 . 103 − 92 . 263 2 . 923    (24) χ 2 H = 12 ∑ i =1 [ H ( z$_{i}$ ) − H$_{ob}$ ( z$_{i}$ )] 2 σ 2 i . (25) χ 2 total = ˜ χ 2 sn + χ 2 cmb + χ 2 bao + χ 2 $_{H}$. (26) IV. FITTING RESULTS A. Model I Models ˜ χ 2 sn,min χ 2 cmb,min χ 2 bao,min χ 2 H,min χ 2 total,min Model I 459.728 0.204 1.494 5.983 467.409 CPL 465.621 0.251 1.716 10.818 478.406 ΛCDM 465.759 1.014 1.470 10.850 479.093 TABLE I: The best-fitted χ 2 of four data sets for Model I, CPL model and the ΛCDM model. 8