drot.f

来自「贝尔实验室多年开发的矩阵计算程序库的说明文件」· F 代码 · 共 50 行

      SUBROUTINE DROT(N,DX,INCX,DY,INCY,C,S)
*     .. Scalar Arguments ..
      DOUBLE PRECISION C,S
      INTEGER INCX,INCY,N
*     ..
*     .. Array Arguments ..
      DOUBLE PRECISION DX(*),DY(*)
*     ..
*
*  Purpose
*  =======
*
*     applies a plane rotation.
*     jack dongarra, linpack, 3/11/78.
*     modified 12/3/93, array(1) declarations changed to array(*)
*
*
*     .. Local Scalars ..
      DOUBLE PRECISION DTEMP
      INTEGER I,IX,IY
*     ..
      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
          DTEMP = C*DX(IX) + S*DY(IY)
          DY(IY) = C*DY(IY) - S*DX(IX)
          DX(IX) = DTEMP
          IX = IX + INCX
          IY = IY + INCY
   10 CONTINUE
      RETURN
*
*       code for both increments equal to 1
*
   20 DO 30 I = 1,N
          DTEMP = C*DX(I) + S*DY(I)
          DY(I) = C*DY(I) - S*DX(I)
          DX(I) = DTEMP
   30 CONTINUE
      RETURN
      END