anchor.diff:  
     210 continue
   c     # zero-order extrapolation:
  -      do 215 m=1,meqn
  -         do 215 ibc=1,mbc
  -            do 215 j = 1-mbc, my+mbc
  +      do m=1,meqn
  +         do ibc=1,mbc
  +            do j = 1-mbc, my+mbc
                  q(mx+ibc,j,m) = q(mx,j,m)
  -  215       continue
  +            end do
  +         end do
  +      end do
         go to 299
   
     220 continue
   c     # periodic:
  -      do 225 m=1,meqn
  -         do 225 ibc=1,mbc
  -            do 225 j = 1-mbc, my+mbc
  +      do m=1,meqn
  +         do ibc=1,mbc
  +            do j = 1-mbc, my+mbc
                  q(mx+ibc,j,m) = q(ibc,j,m)
  -  225       continue
  +            end do
  +         end do
  +      end do
         go to 299
   
     230 continue
   c     # solid wall (assumes 2'nd component is velocity or momentum in x):
  -      do 235 m=1,meqn
  -         do 235 ibc=1,mbc
  -            do 235 j = 1-mbc, my+mbc
  +      do m=1,meqn
  +         do ibc=1,mbc
  +            do j = 1-mbc, my+mbc
                  q(mx+ibc,j,m) = q(mx+1-ibc,j,m)
  -  235       continue
  -c     # negate the normal velocity:
  -      do 236 ibc=1,mbc
  -         do 236 j = 1-mbc, my+mbc
  +            end do
  +         end do
  +      end do
  +c     # negate the normal velocity:
  +      do ibc=1,mbc
  +         do j = 1-mbc, my+mbc
               q(mx+ibc,j,2) = -q(mx+1-ibc,j,2)
  -  236    continue
  +         end do
  +      end do
         go to 299
   
     299 continue
  
positive.code: c
    310 continue
  c     # zero-order extrapolation:
        do 315 m=1,meqn
           do 315 jbc=1,mbc
              do 315 i = 1-mbc, mx+mbc
                 q(i,1-jbc,m) = q(i,1,m)
    315       continue
        go to 399
  
    320 continue
  c     # periodic:
        do 325 m=1,meqn
           do 325 jbc=1,mbc
              do 325 i = 1-mbc, mx+mbc
                 q(i,1-jbc,m) = q(i,my+1-jbc,m)
    325       continue
        go to 399
  
    330 continue
  c     # solid wall (assumes 3'rd component is velocity or momentum in y):
        do 335 m=1,meqn
           do 335 jbc=1,mbc
              do 335 i = 1-mbc, mx+mbc
                 q(i,1-jbc,m) = q(i,jbc,m)
    335       continue
  c     # negate the normal velocity:
        do 336 jbc=1,mbc
           do 336 i = 1-mbc, mx+mbc
              q(i,1-jbc,3) = -q(i,jbc,3)
    336    continue
        go to 399
  
    399 continue
  
negative.code: c     #   (1-ibc, j)   for ibc = 1,mbc,  j = 1-mbc, my+mbc
  c     #   (mx+ibc, j)  for ibc = 1,mbc,  j = 1-mbc, my+mbc
  c
        implicit none
  
        integer maxmx, maxmy, meqn, mbc, mx,my,maux
        double precision xlower, ylower, dx, dy, t, dt
        double precision q(1-mbc:maxmx+mbc, 1-mbc:maxmy+mbc, meqn)
        double precision aux(1-mbc:maxmx+mbc, 1-mbc:maxmy+mbc, *)
        integer mthbc(4)
  
        double precision rinf, vinf, einf
        common /cominf/ rinf,vinf,einf
  
        integer ibc, jbc, i, j, m
  
  c
  c
  c-------------------------------------------------------
  