as quintessence-like form and phantom-like form are roughly equal, and the probabilities that the energy flow streams from dark energy to dark matter and the reverse are also roughly equal. One-dimensional likelihood distribution functions for $w_X$ and $\eta$ are shown in Fig.8 and Fig.9, respectively. It is very clear that the original Chaplygin gas model, $\alpha=1$ (or $\eta=2$) and $w_X=-1$, is totally ruled out by the observational data at $99.7\%$ confidence level. In addition, it should be pointed out that when we fix $\eta=2$ and let $w_X$ free, the NGCG model will be identified as the so-called variable Chaplygin gas (VCG) model proposed in Ref. [@Guo1] (see also Ref. [@Guo2]). The joint analysis of SNe+CMB+LSS also rules out this probability. It is hopeful that the future precise data will provide more strong evidences to judge whether the dark energy is the cosmological constant and whether dark energy and dark matter are in unification.

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Concluding remarks
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The Chaplygin gas model is a proposal to describe dark energy and dark matter as a unified fluid, the Chaplygin gas, characterized by an exotic equation of state $p=-A/\rho$, where $A$ is a positive constant. Since this original Chaplygin gas has 