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The evolution of dark energy density is a crucial quantity in understandingthe nature of dark energy. Often, the quantity is described by the so-calledequation of state, that is the ratio of dark energy pressure to its density. Inthis scenario, the dark energy density is always positive throughout cosmichistory and a negative value is not allowed. Assuming a homogeneous andisotropic universe, we reconstruct the dark energy density directly fromobservational data and investigate its evolution through cosmic history. Weconsider the latest SNIa, BAO and cosmic chronometer data and reconstruct thedark energy density in both flat and non-flat universes up to redshift $z\sim3$. The results are well in agreement with the $\Lambda$CDM up to redshift$z\sim 1.5$, whereas all data and methods, in our analysis, provide a negativedark energy density at high redshifts.

Reconstruction of dark energy density by non-parametric approaches