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subroutine isort1(count,n,index,flag)
c
c !purpose
c isort sort integer array,maintaining an index array
c
c !calling sequence
c subroutine isort1(count,n,index,flag)
c integer n,index(n)
c integer count(n),flag
c
c count : array to be sorted
c n :size of count and index
c index : array containing on return index of sorted array
c flag : 1 : increasing order
c 0 : decreasing order
c
c !method
c quick sort method is used
c !restriction
c n must be less than 2**(50/2) ! due to lengh of work space mark
c !
dimension mark(50),index(n)
integer count(n),av,x,flag
c
c set index array to original order .
do 10 i=1,n
index(i)=i
10 continue
c check that a trivial case has not been entered .
if(n.le.1) goto 300
c 'm' is the length of segment which is short enough to enter
c the final sorting routine. it may be easily changed.
m=12
c set up initial values.
la=2
is=1
if=n
do 190 mloop=1,n
c if segment is short enough sort with final sorting routine .
ifka=if-is
if((ifka+1).gt.m) goto 70
c*********final sorting ***
c ( a simple bubble sort )
is1=is+1
do 60 j=is1,if
i=j
40 if(count(i-1).gt.count(i)) goto 60
if(count(i-1).lt.count(i)) goto 50
if(index(i-1).lt.index(i)) goto 60
50 av=count(i-1)
count(i-1)=count(i)
count(i)=av
int=index(i-1)
index(i-1)=index(i)
index(i)=int
i=i-1
if(i.gt.is) goto 40
60 continue
la=la-2
goto 170
c ******* quicksort ********
c select the number in the central position in the segment as
c the test number.replace it with the number from the segment's
c highest address.
70 iy=(is+if)/2
x=count(iy)
intest=index(iy)
count(iy)=count(if)
index(iy)=index(if)
c the markers 'i' and 'ifk' are used for the beginning and end
c of the section not so far tested against the present value
c of x .
k=1
ifk=if
c we alternate between the outer loop that increases i and the
c inner loop that reduces ifk, moving numbers and indices as
c necessary, until they meet .
do 110 i=is,if
if(x.lt.count(i)) goto 110
if(x.gt.count(i)) goto 80
if(intest.gt.index(i)) goto 110
80 if(i.ge.ifk) goto 120
count(ifk)=count(i)
index(ifk)=index(i)
k1=k
do 100 k=k1,ifka
ifk=if-k
if(count(ifk).lt.x) goto 100
if(count(ifk).gt.x) goto 90
if(intest.le.index(ifk)) goto 100
90 if(i.ge.ifk) goto 130
count(i)=count(ifk)
index(i)=index(ifk)
go to 110
100 continue
goto 120
110 continue
c return the test number to the position marked by the marker
c which did not move last. it divides the initial segment into
c 2 parts. any element in the first part is less than or equal
c to any element in the second part, and they may now be sorted
c independently .
120 count(ifk)=x
index(ifk)=intest
ip=ifk
goto 140
130 count(i)=x
index(i)=intest
ip=i
c store the longer subdivision in workspace.
140 if((ip-is).gt.(if-ip)) goto 150
mark(la)=if
mark(la-1)=ip+1
if=ip-1
goto 160
150 mark(la)=ip-1
mark(la-1)=is
is=ip+1
c find the length of the shorter subdivision.
160 lngth=if-is
if(lngth.le.0) goto 180
c if it contains more than one element supply it with workspace .
la=la+2
goto 190
170 if(la.le.0) goto 200
c obtain the address of the shortest segment awaiting quicksort
180 if=mark(la)
is=mark(la-1)
190 continue
200 continue
if(flag.eq.0) goto 300
do 201 i=1,n/2
j=n+1-i
ii=index(i)
index(i)=index(j)
index(j)=ii
ii=count(i)
count(i)=count(j)
count(j)=ii
201 continue
300 return
end
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