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288 lines
6.1 KiB
Fortran
288 lines
6.1 KiB
Fortran
subroutine ssort (x,y,n,kflag)
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c***purpose sort an array and optionally make the same interchanges in
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c an auxiliary array. the array may be sorted in increasing
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c or decreasing order. a slightly modified quicksort
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c algorithm is used.
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c
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c ssort sorts array x and optionally makes the same interchanges in
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c array y. the array x may be sorted in increasing order or
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c decreasing order. a slightly modified quicksort algorithm is used.
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c
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c description of parameters
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c x - array of values to be sorted
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c y - array to be (optionally) carried along
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c n - number of values in array x to be sorted
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c kflag - control parameter
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c = 2 means sort x in increasing order and carry y along.
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c = 1 means sort x in increasing order (ignoring y)
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c = -1 means sort x in decreasing order (ignoring y)
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c = -2 means sort x in decreasing order and carry y along.
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integer kflag, n
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! real x(n), y(n)
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! real r, t, tt, tty, ty
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integer x(n), y(n)
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integer r, t, tt, tty, ty
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integer i, ij, j, k, kk, l, m, nn
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integer il(21), iu(21)
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nn = n
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if (nn .lt. 1) then
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! print*,'ssort: The number of sort elements is not positive.'
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! print*,'ssort: n = ',nn,' kflag = ',kflag
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return
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endif
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c
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kk = abs(kflag)
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if (kk.ne.1 .and. kk.ne.2) then
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print *,
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+ 'the sort control parameter, k, is not 2, 1, -1, or -2.'
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return
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endif
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c
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c alter array x to get decreasing order if needed
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c
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if (kflag .le. -1) then
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do 10 i=1,nn
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x(i) = -x(i)
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10 continue
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endif
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c
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if (kk .eq. 2) go to 100
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c
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c sort x only
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c
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m = 1
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i = 1
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j = nn
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r = 0.375e0
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c
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20 if (i .eq. j) go to 60
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if (r .le. 0.5898437e0) then
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r = r+3.90625e-2
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else
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r = r-0.21875e0
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endif
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c
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30 k = i
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c
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c select a central element of the array and save it in location t
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c
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ij = i + int((j-i)*r)
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t = x(ij)
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c
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c if first element of array is greater than t, interchange with t
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c
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if (x(i) .gt. t) then
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x(ij) = x(i)
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x(i) = t
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t = x(ij)
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endif
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l = j
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c
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c if last element of array is less than than t, interchange with t
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c
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if (x(j) .lt. t) then
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x(ij) = x(j)
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x(j) = t
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t = x(ij)
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c
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c if first element of array is greater than t, interchange with t
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c
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if (x(i) .gt. t) then
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x(ij) = x(i)
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x(i) = t
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t = x(ij)
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endif
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endif
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c
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c find an element in the second half of the array which is smaller
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c than t
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c
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40 l = l-1
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if (x(l) .gt. t) go to 40
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c
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c find an element in the first half of the array which is greater
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c than t
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c
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50 k = k+1
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if (x(k) .lt. t) go to 50
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c
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c interchange these elements
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c
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if (k .le. l) then
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tt = x(l)
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x(l) = x(k)
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x(k) = tt
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go to 40
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endif
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c
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c save upper and lower subscripts of the array yet to be sorted
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c
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if (l-i .gt. j-k) then
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il(m) = i
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iu(m) = l
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i = k
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m = m+1
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else
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il(m) = k
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iu(m) = j
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j = l
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m = m+1
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endif
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go to 70
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c
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c begin again on another portion of the unsorted array
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c
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60 m = m-1
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if (m .eq. 0) go to 190
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i = il(m)
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j = iu(m)
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c
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70 if (j-i .ge. 1) go to 30
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if (i .eq. 1) go to 20
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i = i-1
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c
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80 i = i+1
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if (i .eq. j) go to 60
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t = x(i+1)
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if (x(i) .le. t) go to 80
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k = i
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c
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90 x(k+1) = x(k)
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k = k-1
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if (t .lt. x(k)) go to 90
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x(k+1) = t
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go to 80
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c
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c sort x and carry y along
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c
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100 m = 1
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i = 1
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j = nn
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r = 0.375e0
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c
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110 if (i .eq. j) go to 150
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if (r .le. 0.5898437e0) then
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r = r+3.90625e-2
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else
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r = r-0.21875e0
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endif
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c
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120 k = i
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c
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c select a central element of the array and save it in location t
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c
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ij = i + int((j-i)*r)
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t = x(ij)
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ty = y(ij)
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c
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c if first element of array is greater than t, interchange with t
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c
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if (x(i) .gt. t) then
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x(ij) = x(i)
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x(i) = t
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t = x(ij)
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y(ij) = y(i)
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y(i) = ty
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ty = y(ij)
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endif
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l = j
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c
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c if last element of array is less than t, interchange with t
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c
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if (x(j) .lt. t) then
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x(ij) = x(j)
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x(j) = t
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t = x(ij)
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y(ij) = y(j)
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y(j) = ty
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ty = y(ij)
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c
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c if first element of array is greater than t, interchange with t
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c
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if (x(i) .gt. t) then
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x(ij) = x(i)
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x(i) = t
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t = x(ij)
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y(ij) = y(i)
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y(i) = ty
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ty = y(ij)
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endif
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endif
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c
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c find an element in the second half of the array which is smaller
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c than t
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c
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130 l = l-1
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if (x(l) .gt. t) go to 130
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c
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c find an element in the first half of the array which is greater
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c than t
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c
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140 k = k+1
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if (x(k) .lt. t) go to 140
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c
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c interchange these elements
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c
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if (k .le. l) then
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tt = x(l)
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x(l) = x(k)
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x(k) = tt
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tty = y(l)
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y(l) = y(k)
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y(k) = tty
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go to 130
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endif
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c
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c save upper and lower subscripts of the array yet to be sorted
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c
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if (l-i .gt. j-k) then
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il(m) = i
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iu(m) = l
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i = k
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m = m+1
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else
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il(m) = k
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iu(m) = j
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j = l
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m = m+1
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endif
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go to 160
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c
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c begin again on another portion of the unsorted array
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c
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150 m = m-1
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if (m .eq. 0) go to 190
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i = il(m)
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j = iu(m)
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c
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160 if (j-i .ge. 1) go to 120
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if (i .eq. 1) go to 110
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i = i-1
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c
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170 i = i+1
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if (i .eq. j) go to 150
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t = x(i+1)
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ty = y(i+1)
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if (x(i) .le. t) go to 170
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k = i
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c
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180 x(k+1) = x(k)
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y(k+1) = y(k)
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k = k-1
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if (t .lt. x(k)) go to 180
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x(k+1) = t
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y(k+1) = ty
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go to 170
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c
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c clean up
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c
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190 if (kflag .le. -1) then
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do 200 i=1,nn
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x(i) = -x(i)
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200 continue
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endif
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return
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end
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