isortqx, ssortqx, dsortqx 

Performs an indexed sort of a vector

FORMAT

  {I,S,D}SORTQX

  ( order, n, x, incx, index )

Arguments

  order               character*1
                      On entry, order specifies the operation to be performed
                      as follows:

                      If order = 'A' or 'a', x is sorted in ascending
                      sequence

                      If order = 'D' or 'd', x is sorted in descending
                      sequence
                      On exit, order is unchanged.

  n                   integer*4
                      On entry, the length of vector x.
                      On exit, n is unchanged.

  x                   integer*4 | real*4 | real*8
                      On entry, a length n vector of data to be sorted.
                      On exit, x is unchanged.

  incx                integer*4
                      On entry, incx specifies the distance between elements
                      of vector x. incx must be positive.
                      On exit, incx is unchanged.

  index               integer*4
                      On entry, the content of index is ignored.
                      On exit, index contains a permuted vector of indices
                      which may be used to access data vector x in the sorted
                      order specified by order.

Description

  The _SORTQX routines sort an indexed vector of data using the quicksort
  algorithm. Data is sorted in ascending order if order is 'A' or 'a' and in
  descending order if order is 'D' or 'd'.  The quicksort algorithm is
  implemented by recursinq until the partition size is less than sixteen. At
  that point a modified insertion sort is used to sort the elements of the
  partition.

Example

  REAL*4 DATA( 100 ),INDEX( 100 )
  N = 100
  CALL SSORTQX( 'A',N,DATA,1,INDEX )
  DO I=1,N
     PRINT *,DATA( INDEX(I) )
  ENDDO

  This FORTRAN code sorts a 100 element single real vector and prints its
  contents in sorted order.