dlamrg.f

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*> \brief \b DLAMRG creates a permutation list to merge the entries of two independently sorted sets into a single set sorted in ascending order.
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at 
*            http://www.netlib.org/lapack/explore-html/ 
*
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*> \endhtmlonly 
*
*  Definition:
*  ===========
*
*       SUBROUTINE DLAMRG( N1, N2, A, DTRD1, DTRD2, INDEX )
* 
*       .. Scalar Arguments ..
*       INTEGER            DTRD1, DTRD2, N1, N2
*       ..
*       .. Array Arguments ..
*       INTEGER            INDEX( * )
*       DOUBLE PRECISION   A( * )
*       ..
*  
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*> DLAMRG will create a permutation list which will merge the elements
*> of A (which is composed of two independently sorted sets) into a
*> single set which is sorted in ascending order.
*> \endverbatim
*
*  Arguments:
*  ==========
*
*> \param[in] N1
*> \verbatim
*>          N1 is INTEGER
*> \endverbatim
*>
*> \param[in] N2
*> \verbatim
*>          N2 is INTEGER
*>         These arguements contain the respective lengths of the two
*>         sorted lists to be merged.
*> \endverbatim
*>
*> \param[in] A
*> \verbatim
*>          A is DOUBLE PRECISION array, dimension (N1+N2)
*>         The first N1 elements of A contain a list of numbers which
*>         are sorted in either ascending or descending order.  Likewise
*>         for the final N2 elements.
*> \endverbatim
*>
*> \param[in] DTRD1
*> \verbatim
*>          DTRD1 is INTEGER
*> \endverbatim
*>
*> \param[in] DTRD2
*> \verbatim
*>          DTRD2 is INTEGER
*>         These are the strides to be taken through the array A.
*>         Allowable strides are 1 and -1.  They indicate whether a
*>         subset of A is sorted in ascending (DTRDx = 1) or descending
*>         (DTRDx = -1) order.
*> \endverbatim
*>
*> \param[out] INDEX
*> \verbatim
*>          INDEX is INTEGER array, dimension (N1+N2)
*>         On exit this array will contain a permutation such that
*>         if B( I ) = A( INDEX( I ) ) for I=1,N1+N2, then B will be
*>         sorted in ascending order.
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee 
*> \author Univ. of California Berkeley 
*> \author Univ. of Colorado Denver 
*> \author NAG Ltd. 
*
*> \date September 2012
*
*> \ingroup auxOTHERcomputational
*
*  =====================================================================
      SUBROUTINE dlamrg( N1, N2, A, DTRD1, DTRD2, INDEX )
*
*  -- LAPACK computational routine (version 3.4.2) --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*     September 2012
*
*     .. Scalar Arguments ..
      INTEGER            dtrd1, dtrd2, n1, n2
*     ..
*     .. Array Arguments ..
      INTEGER            index( * )
      DOUBLE PRECISION   a( * )
*     ..
*
*  =====================================================================
*
*     .. Local Scalars ..
      INTEGER            i, ind1, ind2, n1sv, n2sv
*     ..
*     .. Executable Statements ..
*
      n1sv = n1
      n2sv = n2
      IF( dtrd1.GT.0 ) THEN
         ind1 = 1
      ELSE
         ind1 = n1
      END IF
      IF( dtrd2.GT.0 ) THEN
         ind2 = 1 + n1
      ELSE
         ind2 = n1 + n2
      END IF
      i = 1
*     while ( (N1SV > 0) & (N2SV > 0) )
   10 continue
      IF( n1sv.GT.0 .AND. n2sv.GT.0 ) THEN
         IF( a( ind1 ).LE.a( ind2 ) ) THEN
            index( i ) = ind1
            i = i + 1
            ind1 = ind1 + dtrd1
            n1sv = n1sv - 1
         ELSE
            index( i ) = ind2
            i = i + 1
            ind2 = ind2 + dtrd2
            n2sv = n2sv - 1
         END IF
         go to 10
      END IF
*     end while
      IF( n1sv.EQ.0 ) THEN
         DO 20 n1sv = 1, n2sv
            index( i ) = ind2
            i = i + 1
            ind2 = ind2 + dtrd2
   20    continue
      ELSE
*     N2SV .EQ. 0
         DO 30 n2sv = 1, n1sv
            index( i ) = ind1
            i = i + 1
            ind1 = ind1 + dtrd1
   30    continue
      END IF
*
      return
*
*     End of DLAMRG
*
      END