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! Calculation of shift upwinded differences except at boundaries.
! $Header$
! If this is an active cell...
if ( eh_mask(i,j,k,l) .ge. 0 ) then
! If the shift in the x-direction is <0.
if ( betax(i,j,k) .lt. zero ) then
! If both of the two nearest cells to the right are active cells...
if ( ( eh_mask(i+1,j,k,l) .ge. 0 ) .and. ( eh_mask(i+2,j,k,l) .ge. 0 ) ) then
! Calculate the right handed one sided derivative.
dfx(i,j,k,l) = idx * ( -three * f(i,j,k,l) + &
four * f(i+1,j,k,l) - f(i+2,j,k,l) )
! Else if only the nearest neighbour to the right is active...
else if ( eh_mask(i+1,j,k,l) .ge. 0 ) then
! Calculate the centered derivative.
dfx(i,j,k,l) = idx * ( f(i+1,j,k,l) - f(i-1,j,k,l) )
! Else it must be a boundary cell...
else
! So calculate the left handed one sided derivative.
dfx(i,j,k,l) = idx * ( three * f(i,j,k,l) - &
four * f(i-1,j,k,l) + f(i-2,j,k,l) )
end if
! Else if the shift is >= 0.
else
! If both of the two nearest cells to the left are active cells...
if ( ( eh_mask(i-1,j,k,l) .ge. 0 ) .and. ( eh_mask(i-2,j,k,l) .ge. 0 ) ) then
! Calculate the left handed one sided derivative.
dfx(i,j,k,l) = idx * ( three * f(i,j,k,l) - &
four * f(i-1,j,k,l) + f(i-2,j,k,l) )
! Else if only the nearest neighbour to the left is active...
else if ( eh_mask(i-1,j,k,l) .ge. 0 ) then
! Calculate the centered derivative.
dfx(i,j,k,l) = idx * ( f(i+1,j,k,l) - f(i-1,j,k,l) )
! Else it must be a boundary cell...
else
! So calculate the left handed one sided derivative.
dfx(i,j,k,l) = idx * ( -three * f(i,j,k,l) + &
four * f(i+1,j,k,l) - f(i+2,j,k,l) )
end if
end if
! Ditto for the y-derivative.
if ( betay(i,j,k) .lt. zero ) then
if ( ( eh_mask(i,j+1,k,l) .ge. 0 ) .and. ( eh_mask(i,j+2,k,l) .ge. 0 ) ) then
dfy(i,j,k,l) = idy * ( -three * f(i,j,k,l) + &
four * f(i,j+1,k,l) - f(i,j+2,k,l) )
else if ( eh_mask(i,j+1,k,l) .ge. 0 ) then
dfy(i,j,k,l) = idy * ( f(i,j+1,k,l) - f(i,j-1,k,l) )
else
dfy(i,j,k,l) = idy * ( three * f(i,j,k,l) - &
four * f(i,j-1,k,l) + f(i,j-2,k,l) )
end if
else
if ( ( eh_mask(i,j-1,k,l) .ge. 0 ) .and. ( eh_mask(i,j-2,k,l) .ge. 0 ) ) then
dfy(i,j,k,l) = idy * ( three * f(i,j,k,l) - &
four * f(i,j-1,k,l) + f(i,j-2,k,l) )
else if ( eh_mask(i-1,j,k,l) .ge. 0 ) then
dfy(i,j,k,l) = idy * ( f(i,j+1,k,l) - f(i,j-1,k,l) )
else
dfy(i,j,k,l) = idy * ( -three * f(i,j,k,l) + &
four * f(i,j+1,k,l) - f(i,j+2,k,l) )
end if
end if
! Ditto for the z-derivative.
if ( betaz(i,j,k) .lt. zero ) then
if ( ( eh_mask(i,j,k+1,l) .ge. 0 ) .and. ( eh_mask(i,j,k+2,l) .ge. 0 ) ) then
dfz(i,j,k,l) = idz * ( -three * f(i,j,k,l) + &
four * f(i,j,k+1,l) - f(i,j,k+2,l) )
else if ( eh_mask(i,j,k+1,l) .ge. 0 ) then
dfz(i,j,k,l) = idz * ( f(i,j,k+1,l) - f(i,j,k-1,l) )
else
dfz(i,j,k,l) = idz * ( three * f(i,j,k,l) - &
four * f(i,j,k-1,l) + f(i,j,k-2,l) )
end if
else
if ( ( eh_mask(i,j,k-1,l) .ge. 0 ) .and. ( eh_mask(i,j,k-2,l) .ge. 0 ) ) then
dfz(i,j,k,l) = idz * ( three * f(i,j,k,l) - &
four * f(i,j,k-1,l) + f(i,j,k-2,l) )
else if ( eh_mask(i-1,j,k,l) .ge. 0 ) then
dfz(i,j,k,l) = idz * ( f(i,j,k+1,l) - f(i,j,k-1,l) )
else
dfz(i,j,k,l) = idz * ( -three * f(i,j,k,l) + &
four * f(i,j,k+1,l) - f(i,j,k+2,l) )
end if
end if
! If the cell is not active set the derivatives to zero.
else
dfx(i,j,k,l) = zero
dfy(i,j,k,l) = zero
dfz(i,j,k,l) = zero
end if
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