Inverse problem - reconstruction of dark energy models
  We review how we can construct the gravity models which reproduces the
arbitrary development of the universe. We consider the reconstruction in the
Einstein gravity coupled with generalized perfect fluid, scalar-Einstein
gravity, scalar-Einstein-Gauss-Bonnet gravity, Einstein-$F(G)$-gravity, and
$F(R)$-gravity. Very explicit formulas are given to reconstruct the models,
which could be used when we find the detailed data of the development of the
universe by future observations. Especially we find the formulas using
e-foldings, which has a direct relation with observed redshift. As long as we
observe the time development of the Hubble rate $H$, there exists a variety of
models describing the arbitrary development of universe.
