  We propose a stable first-order relativistic dissipative hydrodynamic
equation in the particle frame (Eckart frame) for the first time. The equation
to be proposed was in fact previously derived by the authors and a collaborator
from the relativistic Boltzmann equation. We demonstrate that the equilibrium
state is stable with respect to the time evolution described by our
hydrodynamic equation in the particle frame. Our equation may be a proper
starting point for constructing second-order causal relativistic hydrodynamics,
to replace Eckart's particle-flow theory.
