subroutine indexx(arr,n,indx) parameter (M=7,NSTACK=50) integer n,indx(n) integer arr(n) integer i,indxt,ir,itemp,j,jstack,k,l,istack(NSTACK) real a do j=1,n indx(j)=j enddo jstack=0 l=1 ir=n 1 if(ir-l.lt.M) then do j=l+1,ir indxt=indx(j) a=arr(indxt) do i=j-1,1,-1 if(arr(indx(i)).le.a) goto 2 indx(i+1)=indx(i) enddo i=0 2 indx(i+1)=indxt enddo if(jstack.eq.0) return ir=istack(jstack) l=istack(jstack-1) jstack=jstack-2 else k=(l+ir)/2 itemp=indx(k) indx(k)=indx(l+1) indx(l+1)=itemp if(arr(indx(l+1)).gt.arr(indx(ir))) then itemp=indx(l+1) indx(l+1)=indx(ir) indx(ir)=itemp endif if(arr(indx(l)).gt.arr(indx(ir))) then itemp=indx(l) indx(l)=indx(ir) indx(ir)=itemp endif if(arr(indx(l+1)).gt.arr(indx(l))) then itemp=indx(l+1) indx(l+1)=indx(l) indx(l)=itemp endif i=l+1 j=ir indxt=indx(l) a=arr(indxt) 3 continue i=i+1 if(arr(indx(i)).lt.a) goto 3 4 continue j=j-1 if(arr(indx(j)).gt.a) goto 4 if(j.lt.i) goto 5 itemp=indx(i) indx(i)=indx(j) indx(j)=itemp goto 3 5 indx(l)=indx(j) indx(j)=indxt jstack=jstack+2 if(jstack.gt.NSTACK) stop 'NSTACK too small in indexx' if(ir-i+1.ge.j-l)then istack(jstack)=ir istack(jstack-1)=i ir=j-1 else istack(jstack)=j-1 istack(jstack-1)=l l=i endif endif goto 1 end subroutine indexx