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