anchor.diff:      step = step + 1
       t1 = t2
       t2 = tdiv + REAL(i)*tstep2
  +
  +    omeg = LOG(f0 / ft) / tstep2
   
       ! Rod bank changes
       DO n = 1, nb
  
positive.code:     step = step + 1
      t1 = t2
      t2 = REAL(i)*tstep1
  
      ! Rod bank changes
      DO n = 1, nb
  
negative.code: 
      ! Modify removal xsec
      sigrp = sigr    ! Save sigr to sigrp
      DO g = 1, ng
         DO n = 1, nnod
            sigr(n,g) = sigr(n,g) + 1. / (velo(g) * tstep1) + omeg(n,g) / velo(g)
         END DO
      END DO
  
      ! Save the previous flux and DN precusor density
      ft = f0
  