dlaord.f

来自「famous linear algebra library (LAPACK) p」· F 代码 · 共 102 行

      SUBROUTINE DLAORD( JOB, N, X, INCX )
*
*  -- LAPACK auxiliary routine (version 3.1) --
*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
*     November 2006
*
*     .. Scalar Arguments ..
      CHARACTER          JOB
      INTEGER            INCX, N
*     ..
*     .. Array Arguments ..
      DOUBLE PRECISION   X( * )
*     ..
*
*  Purpose
*  =======
*
*  DLAORD sorts the elements of a vector x in increasing or decreasing
*  order.
*
*  Arguments
*  =========
*
*  JOB     (input) CHARACTER
*          = 'I':  Sort in increasing order
*          = 'D':  Sort in decreasing order
*
*  N       (input) INTEGER
*          The length of the vector X.
*
*  X       (input/output) DOUBLE PRECISION array, dimension
*                         (1+(N-1)*INCX)
*          On entry, the vector of length n to be sorted.
*          On exit, the vector x is sorted in the prescribed order.
*
*  INCX    (input) INTEGER
*          The spacing between successive elements of X.  INCX >= 0.
*
*  =====================================================================
*
*     .. Local Scalars ..
      INTEGER            I, INC, IX, IXNEXT
      DOUBLE PRECISION   TEMP
*     ..
*     .. External Functions ..
      LOGICAL            LSAME
      EXTERNAL           LSAME
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          ABS
*     ..
*     .. Executable Statements ..
*
      INC = ABS( INCX )
      IF( LSAME( JOB, 'I' ) ) THEN
*
*        Sort in increasing order
*
         DO 20 I = 2, N
            IX = 1 + ( I-1 )*INC
   10       CONTINUE
            IF( IX.EQ.1 )
     $         GO TO 20
            IXNEXT = IX - INC
            IF( X( IX ).GT.X( IXNEXT ) ) THEN
               GO TO 20
            ELSE
               TEMP = X( IX )
               X( IX ) = X( IXNEXT )
               X( IXNEXT ) = TEMP
            END IF
            IX = IXNEXT
            GO TO 10
   20    CONTINUE
*
      ELSE IF( LSAME( JOB, 'D' ) ) THEN
*
*        Sort in decreasing order
*
         DO 40 I = 2, N
            IX = 1 + ( I-1 )*INC
   30       CONTINUE
            IF( IX.EQ.1 )
     $         GO TO 40
            IXNEXT = IX - INC
            IF( X( IX ).LT.X( IXNEXT ) ) THEN
               GO TO 40
            ELSE
               TEMP = X( IX )
               X( IX ) = X( IXNEXT )
               X( IXNEXT ) = TEMP
            END IF
            IX = IXNEXT
            GO TO 30
   40    CONTINUE
      END IF
      RETURN
*
*     End of DLAORD
*
      END