= Dark-energy equation-of-state reconstruction
{title2=$\rho_{\rm de}(z)=\rho_{{\rm de},0}\exp[3\int_0^z(1+w)/(1+z')\,dz']$}
<energy> conservation relates a separately conserved dark-energy density to its equation-of-state history. Distance measurements integrate the associated expansion history, making rapid variation difficult to recover uniquely. Growth and potential-evolution probes add information but depend on gravity and clustering assumptions. Consistency with $w=-1$ over a measured interval cannot prove that a field is exactly constant everywhere.
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