  Exoplanets discovered over the last decades have provided a new sample of
giant exoplanets, hot Jupiters. For lack of enough materials in current
locations of hot Jupiters, they are perceived to form outside snowline. Then,
migrate to the locations observed through interactions with gas disks or
high-eccentricity mechanisms. We examined the efficiencies of different
high-eccentricity mechanisms to form hot Jupiters in near coplaner multi-planet
systems. These mechanisms include planet-planet scattering, Kozai-Lidov
mechanism, coplanar high-eccentricity migration, secular chaos, as well as
other two new mechanisms we find in this work, which can produce hot Jupiters
with high inclinations even retrograde. We find Kozai-Lidov mechanism plays the
most important role in producing hot Jupiters among these mechanisms. Secular
chaos is not the usual channel for the formation of hot Jupiters due to the
lack of angular momentum deficit within 10^7 Tin (periods of the inner orbit).
According to comparisons between the observations and simulations, we speculate
that there are at least two populations of hot Jupiters. One population
migrates into the boundary of tidal effects due to interactions with gas disk,
such as ups And b, WASP-47 b and HIP 14810 b. These systems usually have at
least two planets with lower eccentricities, and keep dynamical stable in
compact orbital configurations. Another population forms through
high-eccentricity mechanisms after the excitation of eccentricity due to
dynamical instability. This kind of hot Jupiters usually has Jupiterlike
companions in distant orbits with moderate or high eccentricities.
