About matter and dark-energy domination eras in R^n gravity or lack
  thereof
  We provide further numerical evidence which shows that R^n models in f(R)
metric gravity whether produces a late time acceleration in the Universe or a
matter domination era (usually a transient one) but not both. Our results
confirm the findings of Amendola et al. (2007), but using a different approach
that avoids the mapping to scalar-tensor theories of gravity, and therefore,
dispense us from any discussion or debate about frames (Einstein vs Jordan)
which are endemic in this subject. This class of models has been used
extensively in the literature as an alternative to the dark energy, but should
be considered ruled out for being inconsistent with observations. Finally, we
discuss a caveat in the analysis by Faraoni (2011), which was used to further
constrain these models by using a chameleon mechanism.
