anchor.diff:             read(parsed_line, *) iv, prm(k + 1 : k + nclasses)
           else if (nfields == nclasses**2 + 2) then
              read(parsed_line, *) jv, iv
  +           if (jv > iv) then
  +              write(0,*) "ERROR: when reading couplings line p q {couplings}, it must be q > p"
  +              stop
  +           end if
              k = (2 * nvars - jv) * (jv - 1) / 2 + iv - jv
              k = nvars * nclasses + (k - 1) * nclasses**2
              read(parsed_line, *) jv, iv, prm(k + 1 : k + nclasses**2)
  
positive.code:      ! read nvars
       call parse_next_line(unt, line, parsed_line, nfields, err)
       if (err < 0) then
          write(0,*) "ERROR: invalid formatted input file"
          stop
       end if
       read(parsed_line, *, iostat=err) nvars
  
negative.code:      ! read ndata
       call parse_next_line(unt, line, parsed_line, nfields, err)
       if (err < 0) then
          write(0,*) "ERROR: invalid input file"
          stop
       end if
       read(parsed_line, *, iostat=err) ndata
  