anchor.diff:         open(newunit=lun, file=trim(outfile), status="old", position="append")
       endif
   
  -100 format(1x, g20.10, 1x, g20.10)
  -    write(unit=lun,fmt=100) t, mach_max
  +100 format(1x, g20.10, 1x, g20.10, 1x, g20.10)
  +    write(unit=lun,fmt=100) t, mach_max, mach_L2
   
       close (unit=lun)
   
  
positive.code:     character (len=256) :: outfile
  
      mach_max = -1.d33
  
      do i = U%grid%lo, U%grid%hi
  
  
negative.code:     real (kind=dp_t), intent(in) :: t
      integer, intent(in) :: n
  
      real (kind=dp_t) :: mach_max, mach_L2, M
  
      real (kind=dp_t) :: e, rho, p
  
  