Notes on $f(T)$ Theories
  The cosmological models based on teleparallel gravity with nonzero torsion
are considered. To investigate the evolution of this theory, we consider the
phase-space analysis of the $f(T)$ theory. It shows when the tension scalar can
be written as an inverse function of $x$ where $x=\rho_{e}/(3m_{pl}^{2}H^{2})$
and $T=g(x)$, the system is an autonomous one. Furthermore,the
$\omega_{e}-\omega'_{e}$ phase analysis is given out. We perform the dynamical
analysis for the models $f(T)=\beta T\ln(T/T_{0})$ and $f(T)=\alpha
m_{pl}^{2}(-T/m_{pl}^{2})^{n}$ particularly. We find that the universe will
settle into de-Sitter phase for both models. And we have examined the evolution
behavior of the power law form in the $\omega_{ep}-\omega'_{ep}$ plane.
