Direct reconstruction of dynamical dark energy from observational Hubble
  parameter data
  Reconstructing the evolution history of the dark energy equation of state
parameter $w(z)$ directly from observational data is highly valuable in
cosmology, since it contains substantial clues in understanding the nature of
the accelerated expansion of the Universe. Many works have focused on
reconstructing $w(z)$ using Type Ia supernova data, however, only a few studies
pay attention to Hubble parameter data. In the present work, we explore the
merit of Hubble parameter data and make an attempt to reconstruct $w(z)$ from
them through the principle component analysis approach. We find that current
Hubble parameter data perform well in reconstructing $w(z)$; though, when
compared to supernova data, the data are scant and their quality is worse. Both
$\Lambda$CDM and evolving $w(z)$ models can be constrained within $10\%$ at
redshifts
  $z \lesssim 1.5$ and even $5\%$ at redshifts 0.1 $\lesssim$ z $\lesssim$ 1 by
using simulated $H(z)$ data of observational quality.
