lapack/SRC/clacrt.f

*> \brief \b CLACRT performs a linear transformation of a pair of complex vectors.
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at
*            http://www.netlib.org/lapack/explore-html/
*
*> \htmlonly
*> Download CLACRT + dependencies
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*> [TGZ]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/clacrt.f">
*> [ZIP]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/clacrt.f">
*> [TXT]</a>
*> \endhtmlonly
*
*  Definition:
*  ===========
*
*       SUBROUTINE CLACRT( N, CX, INCX, CY, INCY, C, S )
*
*       .. Scalar Arguments ..
*       INTEGER            INCX, INCY, N
*       COMPLEX            C, S
*       ..
*       .. Array Arguments ..
*       COMPLEX            CX( * ), CY( * )
*       ..
*
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*> CLACRT performs the operation
*>
*>    (  c  s )( x )  ==> ( x )
*>    ( -s  c )( y )      ( y )
*>
*> where c and s are complex and the vectors x and y are complex.
*> \endverbatim
*
*  Arguments:
*  ==========
*
*> \param[in] N
*> \verbatim
*>          N is INTEGER
*>          The number of elements in the vectors CX and CY.
*> \endverbatim
*>
*> \param[in,out] CX
*> \verbatim
*>          CX is COMPLEX array, dimension (N)
*>          On input, the vector x.
*>          On output, CX is overwritten with c*x + s*y.
*> \endverbatim
*>
*> \param[in] INCX
*> \verbatim
*>          INCX is INTEGER
*>          The increment between successive values of CX.  INCX <> 0.
*> \endverbatim
*>
*> \param[in,out] CY
*> \verbatim
*>          CY is COMPLEX array, dimension (N)
*>          On input, the vector y.
*>          On output, CY is overwritten with -s*x + c*y.
*> \endverbatim
*>
*> \param[in] INCY
*> \verbatim
*>          INCY is INTEGER
*>          The increment between successive values of CY.  INCY <> 0.
*> \endverbatim
*>
*> \param[in] C
*> \verbatim
*>          C is COMPLEX
*> \endverbatim
*>
*> \param[in] S
*> \verbatim
*>          S is COMPLEX
*>          C and S define the matrix
*>             [  C   S  ].
*>             [ -S   C  ]
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \ingroup complexOTHERauxiliary
*
*  =====================================================================
      SUBROUTINE CLACRT( N, CX, INCX, CY, INCY, C, S )
*
*  -- LAPACK auxiliary routine --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
*     .. Scalar Arguments ..
      INTEGER            INCX, INCY, N
      COMPLEX            C, S
*     ..
*     .. Array Arguments ..
      COMPLEX            CX( * ), CY( * )
*     ..
*
* =====================================================================
*
*     .. Local Scalars ..
      INTEGER            I, IX, IY
      COMPLEX            CTEMP
*     ..
*     .. Executable Statements ..
*
      IF( N.LE.0 )
     $   RETURN
      IF( INCX.EQ.1 .AND. INCY.EQ.1 )
     $   GO TO 20
*
*     Code for unequal increments or equal increments not equal to 1
*
      IX = 1
      IY = 1
      IF( INCX.LT.0 )
     $   IX = ( -N+1 )*INCX + 1
      IF( INCY.LT.0 )
     $   IY = ( -N+1 )*INCY + 1
      DO 10 I = 1, N
         CTEMP = C*CX( IX ) + S*CY( IY )
         CY( IY ) = C*CY( IY ) - S*CX( IX )
         CX( IX ) = CTEMP
         IX = IX + INCX
         IY = IY + INCY
   10 CONTINUE
      RETURN
*
*     Code for both increments equal to 1
*
   20 CONTINUE
      DO 30 I = 1, N
         CTEMP = C*CX( I ) + S*CY( I )
         CY( I ) = C*CY( I ) - S*CX( I )
         CX( I ) = CTEMP
   30 CONTINUE
      RETURN
      END