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