!----------------------------------------------------------------------- !BOP! !ROUTINE:  steepz --- Calculate attributes for PPM!! !INTERFACE:      subroutine steepz(i1, i2, km, a4, df2, dm, dq, dp, d4)! !USES:      use precision      implicit none! !INPUT PARAMETERS:      integer km                        ! Total levels      integer i1                        ! Starting longitude      integer i2                        ! Finishing longitude      real(r8)  dp(i1:i2,km)            ! grid size      real(r8)  dq(i1:i2,km)            ! backward diff of q      real(r8)  d4(i1:i2,km)            ! backward sum:  dp(k)+ dp(k-1)       real(r8) df2(i1:i2,km)            ! first guess mismatch      real(r8)  dm(i1:i2,km)            ! monotonic mismatch! !INPUT/OUTPUT PARAMETERS:      real(r8)  a4(4,i1:i2,km)          ! first guess/steepened!! !DESCRIPTION:!   This is complicated stuff related to the Piecewise Parabolic Method!   and I need to read the Collela/Woodward paper before documenting!   thoroughly.!! !REVISION HISTORY: !   ??.??.??    Lin?       Creation!   01.03.26    Sawyer     Added ProTeX documentation!!EOP!-----------------------------------------------------------------------!BOC!! !LOCAL VARIABLES:      integer i, k      real(r8) alfa(i1:i2,km)      real(r8)    f(i1:i2,km)      real(r8)  rat(i1:i2,km)      real(r8)  dg2! Compute ratio of dq/dp      do k=2,km         do i=i1,i2            rat(i,k) = dq(i,k-1) / d4(i,k)         enddo      enddo! Compute F      do k=2,km-1         do i=i1,i2            f(i,k) = (rat(i,k+1) - rat(i,k))                             &                     / ( dp(i,k-1)+dp(i,k)+dp(i,k+1) )         enddo      enddo      do k=3,km-2         do i=i1,i2         if(f(i,k+1)*f(i,k-1).lt.0. .and. df2(i,k).ne.0.) then            dg2 = (f(i,k+1)-f(i,k-1))*((dp(i,k+1)-dp(i,k-1))**2          &                   + d4(i,k)*d4(i,k+1) )            alfa(i,k) = max(0., min(0.5, -0.1875*dg2/df2(i,k)))          else            alfa(i,k) = 0.         endif         enddo      enddo      do k=4,km-2         do i=i1,i2            a4(2,i,k) = (1.-alfa(i,k-1)-alfa(i,k)) * a4(2,i,k) +         &                        alfa(i,k-1)*(a4(1,i,k)-dm(i,k))    +             &                        alfa(i,k)*(a4(1,i,k-1)+dm(i,k-1))         enddo      enddo      return!EOC      end subroutine steepz!-----------------------------------------------------------------------