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Barotropic weight vectorization #202

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Sep 14, 2022
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Barotropic weight vectorization #202

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28 changes: 16 additions & 12 deletions src/core/MOM_barotropic.F90
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Original file line number Diff line number Diff line change
Expand Up @@ -398,6 +398,10 @@ module MOM_barotropic
character*(20), parameter :: BT_CONT_STRING = "FROM_BT_CONT"
!>@}

!> A negligible parameter which avoids division by zero, but is too small to
!! modify physical values.
real, parameter :: subroundoff = 1e-30

contains

!> This subroutine time steps the barotropic equations explicitly.
Expand Down Expand Up @@ -1001,23 +1005,23 @@ subroutine btstep(U_in, V_in, eta_in, dt, bc_accel_u, bc_accel_v, forces, pbce,

!$OMP parallel do default(shared) private(visc_rem)
do k=1,nz ; do j=js,je ; do I=is-1,ie
! rem needs greater than visc_rem_u and 1-Instep/visc_rem_u.
! rem needs to be greater than visc_rem_u and 1-Instep/visc_rem_u.
! The 0.5 below is just for safety.
if (visc_rem_u(I,j,k) <= 0.0) then ; visc_rem = 0.0
elseif (visc_rem_u(I,j,k) >= 1.0) then ; visc_rem = 1.0
elseif (visc_rem_u(I,j,k)**2 > visc_rem_u(I,j,k) - 0.5*Instep) then
visc_rem = visc_rem_u(I,j,k)
else ; visc_rem = 1.0 - 0.5*Instep/visc_rem_u(I,j,k) ; endif
! NOTE: subroundoff is a neglible value used to prevent division by zero.
! When 1-0.5*Instep/visc_rem exceeds visc_rem, the subroundoff is too small
! to modify the significand. When visc_rem is small, the max() operators
! select visc_rem or 0. So subroundoff cannot impact the final value.
visc_rem = min(visc_rem_u(I,j,k), 1.)
visc_rem = max(visc_rem, 1. - 0.5 * Instep / (visc_rem + subroundoff))
visc_rem = max(visc_rem, 0.)
wt_u(I,j,k) = CS%frhatu(I,j,k) * visc_rem
enddo ; enddo ; enddo
!$OMP parallel do default(shared) private(visc_rem)
do k=1,nz ; do J=js-1,je ; do i=is,ie
! rem needs greater than visc_rem_v and 1-Instep/visc_rem_v.
if (visc_rem_v(i,J,k) <= 0.0) then ; visc_rem = 0.0
elseif (visc_rem_v(i,J,k) >= 1.0) then ; visc_rem = 1.0
elseif (visc_rem_v(i,J,k)**2 > visc_rem_v(i,J,k) - 0.5*Instep) then
visc_rem = visc_rem_v(i,J,k)
else ; visc_rem = 1.0 - 0.5*Instep/visc_rem_v(i,J,k) ; endif
! As above, rem must be greater than visc_rem_v and 1-Instep/visc_rem_v.
visc_rem = min(visc_rem_v(I,j,k), 1.)
visc_rem = max(visc_rem, 1. - 0.5 * Instep / (visc_rem + subroundoff))
visc_rem = max(visc_rem, 0.)
wt_v(i,J,k) = CS%frhatv(i,J,k) * visc_rem
enddo ; enddo ; enddo

Expand Down