  An efficient numerical scheme based on the scalar auxiliary variable (SAV)
and marker and cell scheme (MAC) is constructed for the Navier-Stokes
equations. A particular feature of the scheme is that the nonlinear term is
treated explicitly while being unconditionally energy stable. A rigorous error
analysis is carried out to show that both velocity and pressure approximations
are second-order accurate in time and space. Numerical experiments are
presented to verify the theoretical results.
