聖事問荅Sheng shi wen da.

Contient : I聖號經Sheng hao jing ; II天主經Tian zhu jing ; III聖母經Sheng mu jing ; IV信經Xin jing ; V天主十誡Tian zhu shi jie ; VI悔罪經Hui zui jing ; VII要理問荅Yao li wen da ; VIII告解要理Gao jie yao li ; IX聖體問荅Sheng ti wen da ; X-XVIII

Comment on “A modified leapfrog scheme for shallow water equations” by Wen-Yih Sun and Oliver M.T. Sun

A recent paper published in this journal considers the numerical integration of the shallow-water equations using the leapfrog time-stepping scheme [Sun Wen-Yih, Sun Oliver MT. A modified leapfrog scheme for shallow water equations. Comput Fluids 2011;52:69–72]. The authors of that paper propose using the time-averaged height in the numerical calculation of the pressure-gradient force, instead of the instantaneous height at the middle time step. The authors show that this modification doubles the maximum Courant number (and hence the maximum time step) at which the integrations are stable, doubling the computational efficiency. Unfortunately, the pressure-averaging technique proposed by the authors is not original. It was devised and published by Shuman [5] and has been widely used in the atmosphere and ocean modelling community for over 40 years.