anchor.diff:        NT00=NTOT+1
         A(1)=A(NTOT2+3)
         A(2)=A(NTOT2+4)
  -   21 do I=NT00,NTOP,2
  +      do I=NT00,NTOP,2
           A(I)=A(I+2)
           A(I+1)=A(I+3)
         end do
  
positive.code: C    otherwise, periods are specified by user (maximum is 200 periods)
  C -------------------------------------------------------------------
        if (KPER.eq. 0) go to 99
          read(5,'(A32)') FPERIOD
          write(6,60) FPERIOD
     60   format(' File from which periods were read: ' A32)
          open(8,FILE=FPERIOD,STATUS='OLD')
          read (8,4) NLINES, NNM
          do I = 1, NLINES
            read(8,*) headerd
            write(6,*) headerd
          end do
          read(8,*) (T(I), I=1, NNM)
          close(8)
          go to 101
  C ----------------------------------------------------------------------
  C  default periods for calculating response spectra
  C  ---------------------------------------------------------------------
  
negative.code: C     MOVE LAST HALF OF A(J)S DOWN ONE SLOT AND ADD A(N) AT BOTTOM TO
  C     GIVE ARRAY FOR A1PRIME AND A2PRIME CALCULATION
  C
        do I=1,NTOT,2
          J0=NTOT2+2-I
          A(J0)=A(J0-2)
          A(J0+1)=A(J0-1)
        end do
        A(NTOT2+3)=A(1)
        A(NTOT2+4)=A(2)
  C
  