SLATEC Routines --- ISORT ---

*DECK ISORT
      SUBROUTINE ISORT (IX, IY, N, KFLAG)
C***BEGIN PROLOGUE  ISORT
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***LIBRARY   SLATEC
C***CATEGORY  N6A2A
C***TYPE      INTEGER (SSORT-S, DSORT-D, ISORT-I)
C***KEYWORDS  SINGLETON QUICKSORT, SORT, SORTING
C***AUTHOR  Jones, R. E., (SNLA)
C           Kahaner, D. K., (NBS)
C           Wisniewski, J. A., (SNLA)
C***DESCRIPTION
C
C   ISORT sorts array IX and optionally makes the same interchanges in
C   array IY.  The array IX may be sorted in increasing order or
C   decreasing order.  A slightly modified quicksort algorithm is used.
C
C   Description of Parameters
C      IX - integer array of values to be sorted
C      IY - integer array to be (optionally) carried along
C      N  - number of values in integer array IX to be sorted
C      KFLAG - control parameter
C            =  2  means sort IX in increasing order and carry IY along.
C            =  1  means sort IX in increasing order (ignoring IY)
C            = -1  means sort IX in decreasing order (ignoring IY)
C            = -2  means sort IX in decreasing order and carry IY along.
C
C***REFERENCES  R. C. Singleton, Algorithm 347, An efficient algorithm
C                 for sorting with minimal storage, Communications of
C                 the ACM, 12, 3 (1969), pp. 185-187.
C***ROUTINES CALLED  XERMSG
C***REVISION HISTORY  (YYMMDD)
C   761118  DATE WRITTEN
C   810801  Modified by David K. Kahaner.
C   890531  Changed all specific intrinsics to generic.  (WRB)
C   890831  Modified array declarations.  (WRB)
C   891009  Removed unreferenced statement labels.  (WRB)
C   891009  REVISION DATE from Version 3.2
C   891214  Prologue converted to Version 4.0 format.  (BAB)
C   900315  CALLs to XERROR changed to CALLs to XERMSG.  (THJ)
C   901012  Declared all variables; changed X,Y to IX,IY. (M. McClain)
C   920501  Reformatted the REFERENCES section.  (DWL, WRB)
C   920519  Clarified error messages.  (DWL)
C   920801  Declarations section rebuilt and code restructured to use
C           IF-THEN-ELSE-ENDIF.  (RWC, WRB)
C***END PROLOGUE  ISORT