slasrt.f.html

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      SUBROUTINE <a name="SLASRT.1"></a><a href="slasrt.f.html#SLASRT.1">SLASRT</a>( ID, N, D, INFO )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  -- LAPACK routine (version 3.1) --
</span><span class="comment">*</span><span class="comment">     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
</span><span class="comment">*</span><span class="comment">     November 2006
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     .. Scalar Arguments ..
</span>      CHARACTER          ID
      INTEGER            INFO, N
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Array Arguments ..
</span>      REAL               D( * )
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Purpose
</span><span class="comment">*</span><span class="comment">  =======
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Sort the numbers in D in increasing order (if ID = 'I') or
</span><span class="comment">*</span><span class="comment">  in decreasing order (if ID = 'D' ).
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Use Quick Sort, reverting to Insertion sort on arrays of
</span><span class="comment">*</span><span class="comment">  size &lt;= 20. Dimension of STACK limits N to about 2**32.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Arguments
</span><span class="comment">*</span><span class="comment">  =========
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  ID      (input) CHARACTER*1
</span><span class="comment">*</span><span class="comment">          = 'I': sort D in increasing order;
</span><span class="comment">*</span><span class="comment">          = 'D': sort D in decreasing order.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  N       (input) INTEGER
</span><span class="comment">*</span><span class="comment">          The length of the array D.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  D       (input/output) REAL array, dimension (N)
</span><span class="comment">*</span><span class="comment">          On entry, the array to be sorted.
</span><span class="comment">*</span><span class="comment">          On exit, D has been sorted into increasing order
</span><span class="comment">*</span><span class="comment">          (D(1) &lt;= ... &lt;= D(N) ) or into decreasing order
</span><span class="comment">*</span><span class="comment">          (D(1) &gt;= ... &gt;= D(N) ), depending on ID.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  INFO    (output) INTEGER
</span><span class="comment">*</span><span class="comment">          = 0:  successful exit
</span><span class="comment">*</span><span class="comment">          &lt; 0:  if INFO = -i, the i-th argument had an illegal value
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  =====================================================================
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     .. Parameters ..
</span>      INTEGER            SELECT
      PARAMETER          ( SELECT = 20 )
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Local Scalars ..
</span>      INTEGER            DIR, ENDD, I, J, START, STKPNT
      REAL               D1, D2, D3, DMNMX, TMP
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Local Arrays ..
</span>      INTEGER            STACK( 2, 32 )
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. External Functions ..
</span>      LOGICAL            <a name="LSAME.58"></a><a href="lsame.f.html#LSAME.1">LSAME</a>
      EXTERNAL           <a name="LSAME.59"></a><a href="lsame.f.html#LSAME.1">LSAME</a>
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. External Subroutines ..
</span>      EXTERNAL           <a name="XERBLA.62"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Executable Statements ..
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Test the input paramters.
</span><span class="comment">*</span><span class="comment">
</span>      INFO = 0
      DIR = -1
      IF( <a name="LSAME.70"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( ID, <span class="string">'D'</span> ) ) THEN
         DIR = 0
      ELSE IF( <a name="LSAME.72"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( ID, <span class="string">'I'</span> ) ) THEN
         DIR = 1
      END IF
      IF( DIR.EQ.-1 ) THEN
         INFO = -1
      ELSE IF( N.LT.0 ) THEN
         INFO = -2
      END IF
      IF( INFO.NE.0 ) THEN
         CALL <a name="XERBLA.81"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>( <span class="string">'<a name="SLASRT.81"></a><a href="slasrt.f.html#SLASRT.1">SLASRT</a>'</span>, -INFO )
         RETURN
      END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Quick return if possible
</span><span class="comment">*</span><span class="comment">
</span>      IF( N.LE.1 )
     $   RETURN
<span class="comment">*</span><span class="comment">
</span>      STKPNT = 1
      STACK( 1, 1 ) = 1
      STACK( 2, 1 ) = N
   10 CONTINUE
      START = STACK( 1, STKPNT )
      ENDD = STACK( 2, STKPNT )
      STKPNT = STKPNT - 1
      IF( ENDD-START.LE.SELECT .AND. ENDD-START.GT.0 ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Do Insertion sort on D( START:ENDD )
</span><span class="comment">*</span><span class="comment">
</span>         IF( DIR.EQ.0 ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Sort into decreasing order
</span><span class="comment">*</span><span class="comment">
</span>            DO 30 I = START + 1, ENDD
               DO 20 J = I, START + 1, -1
                  IF( D( J ).GT.D( J-1 ) ) THEN
                     DMNMX = D( J )
                     D( J ) = D( J-1 )
                     D( J-1 ) = DMNMX
                  ELSE
                     GO TO 30
                  END IF
   20          CONTINUE
   30       CONTINUE
<span class="comment">*</span><span class="comment">
</span>         ELSE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Sort into increasing order
</span><span class="comment">*</span><span class="comment">
</span>            DO 50 I = START + 1, ENDD
               DO 40 J = I, START + 1, -1
                  IF( D( J ).LT.D( J-1 ) ) THEN
                     DMNMX = D( J )
                     D( J ) = D( J-1 )
                     D( J-1 ) = DMNMX
                  ELSE
                     GO TO 50
                  END IF
   40          CONTINUE
   50       CONTINUE
<span class="comment">*</span><span class="comment">
</span>         END IF
<span class="comment">*</span><span class="comment">
</span>      ELSE IF( ENDD-START.GT.SELECT ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Partition D( START:ENDD ) and stack parts, largest one first
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Choose partition entry as median of 3
</span><span class="comment">*</span><span class="comment">
</span>         D1 = D( START )
         D2 = D( ENDD )
         I = ( START+ENDD ) / 2
         D3 = D( I )
         IF( D1.LT.D2 ) THEN
            IF( D3.LT.D1 ) THEN
               DMNMX = D1
            ELSE IF( D3.LT.D2 ) THEN
               DMNMX = D3
            ELSE
               DMNMX = D2
            END IF
         ELSE
            IF( D3.LT.D2 ) THEN
               DMNMX = D2
            ELSE IF( D3.LT.D1 ) THEN
               DMNMX = D3
            ELSE
               DMNMX = D1
            END IF
         END IF
<span class="comment">*</span><span class="comment">
</span>         IF( DIR.EQ.0 ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Sort into decreasing order
</span><span class="comment">*</span><span class="comment">
</span>            I = START - 1
            J = ENDD + 1
   60       CONTINUE
   70       CONTINUE
            J = J - 1
            IF( D( J ).LT.DMNMX )
     $         GO TO 70
   80       CONTINUE
            I = I + 1
            IF( D( I ).GT.DMNMX )
     $         GO TO 80
            IF( I.LT.J ) THEN
               TMP = D( I )
               D( I ) = D( J )
               D( J ) = TMP
               GO TO 60
            END IF
            IF( J-START.GT.ENDD-J-1 ) THEN
               STKPNT = STKPNT + 1
               STACK( 1, STKPNT ) = START
               STACK( 2, STKPNT ) = J
               STKPNT = STKPNT + 1
               STACK( 1, STKPNT ) = J + 1
               STACK( 2, STKPNT ) = ENDD
            ELSE
               STKPNT = STKPNT + 1
               STACK( 1, STKPNT ) = J + 1
               STACK( 2, STKPNT ) = ENDD
               STKPNT = STKPNT + 1
               STACK( 1, STKPNT ) = START
               STACK( 2, STKPNT ) = J
            END IF
         ELSE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Sort into increasing order
</span><span class="comment">*</span><span class="comment">
</span>            I = START - 1
            J = ENDD + 1
   90       CONTINUE
  100       CONTINUE
            J = J - 1
            IF( D( J ).GT.DMNMX )
     $         GO TO 100
  110       CONTINUE
            I = I + 1
            IF( D( I ).LT.DMNMX )
     $         GO TO 110
            IF( I.LT.J ) THEN
               TMP = D( I )
               D( I ) = D( J )
               D( J ) = TMP
               GO TO 90
            END IF
            IF( J-START.GT.ENDD-J-1 ) THEN
               STKPNT = STKPNT + 1
               STACK( 1, STKPNT ) = START
               STACK( 2, STKPNT ) = J
               STKPNT = STKPNT + 1
               STACK( 1, STKPNT ) = J + 1
               STACK( 2, STKPNT ) = ENDD
            ELSE
               STKPNT = STKPNT + 1
               STACK( 1, STKPNT ) = J + 1
               STACK( 2, STKPNT ) = ENDD
               STKPNT = STKPNT + 1
               STACK( 1, STKPNT ) = START
               STACK( 2, STKPNT ) = J
            END IF
         END IF
      END IF
      IF( STKPNT.GT.0 )
     $   GO TO 10
      RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     End of <a name="SLASRT.241"></a><a href="slasrt.f.html#SLASRT.1">SLASRT</a>
</span><span class="comment">*</span><span class="comment">
</span>      END

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