dscal.f

贝尔实验室多年开发的矩阵计算程序库的说明文件

      SUBROUTINE DSCAL(N,DA,DX,INCX)
*     .. Scalar Arguments ..
      DOUBLE PRECISION DA
      INTEGER INCX,N
*     ..
*     .. Array Arguments ..
      DOUBLE PRECISION DX(*)
*     ..
*
*  Purpose
*  =======
**
*     scales a vector by a constant.
*     uses unrolled loops for increment equal to one.
*     jack dongarra, linpack, 3/11/78.
*     modified 3/93 to return if incx .le. 0.
*     modified 12/3/93, array(1) declarations changed to array(*)
*
*
*     .. Local Scalars ..
      INTEGER I,M,MP1,NINCX
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC MOD
*     ..
      IF (N.LE.0 .OR. INCX.LE.0) RETURN
      IF (INCX.EQ.1) GO TO 20
*
*        code for increment not equal to 1
*
      NINCX = N*INCX
      DO 10 I = 1,NINCX,INCX
          DX(I) = DA*DX(I)
   10 CONTINUE
      RETURN
*
*        code for increment equal to 1
*
*
*        clean-up loop
*
   20 M = MOD(N,5)
      IF (M.EQ.0) GO TO 40
      DO 30 I = 1,M
          DX(I) = DA*DX(I)
   30 CONTINUE
      IF (N.LT.5) RETURN
   40 MP1 = M + 1
      DO 50 I = MP1,N,5
          DX(I) = DA*DX(I)
          DX(I+1) = DA*DX(I+1)
          DX(I+2) = DA*DX(I+2)
          DX(I+3) = DA*DX(I+3)
          DX(I+4) = DA*DX(I+4)
   50 CONTINUE
      RETURN
      END