csrot.f

贝尔实验室多年开发的矩阵计算程序库的说明文件

      SUBROUTINE CSROT( N, CX, INCX, CY, INCY, C, S )
*
*     .. Scalar Arguments ..
      INTEGER           INCX, INCY, N
      REAL              C, S
*     ..
*     .. Array Arguments ..
      COMPLEX           CX( * ), CY( * )
*     ..
*
*  Purpose
*  =======
*
*  Applies a plane rotation, where the cos and sin (c and s) are real
*  and the vectors cx and cy are complex.
*  jack dongarra, linpack, 3/11/78.
*
*  Arguments
*  ==========
*
*  N        (input) INTEGER
*           On entry, N specifies the order of the vectors cx and cy.
*           N must be at least zero.
*           Unchanged on exit.
*
*  CX       (input) COMPLEX array, dimension at least
*           ( 1 + ( N - 1 )*abs( INCX ) ).
*           Before entry, the incremented array CX must contain the n
*           element vector cx. On exit, CX is overwritten by the updated
*           vector cx.
*
*  INCX     (input) INTEGER
*           On entry, INCX specifies the increment for the elements of
*           CX. INCX must not be zero.
*           Unchanged on exit.
*
*  CY       (input) COMPLEX array, dimension at least
*           ( 1 + ( N - 1 )*abs( INCY ) ).
*           Before entry, the incremented array CY must contain the n
*           element vector cy. On exit, CY is overwritten by the updated
*           vector cy.
*
*  INCY     (input) INTEGER
*           On entry, INCY specifies the increment for the elements of
*           CY. INCY must not be zero.
*           Unchanged on exit.
*
*  C        (input) REAL
*           On entry, C specifies the cosine, cos.
*           Unchanged on exit.
*
*  S        (input) REAL
*           On entry, S specifies the sine, sin.
*           Unchanged on exit.
*
*  =====================================================================
*
*     .. 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 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