dscal Subroutine

public subroutine dscal(n, da, dx, incx)

NAME

dscal(3f) - [BLAS:DOUBLE_BLAS_LEVEL1] scales a vector by a constant.

SYNOPSIS

 subroutine dscal(n,da,dx,incx)

   .. Scalar Arguments ..
   double precision,intent(in)    :: da
   integer,intent(in)             :: incx,n
   ..
   .. Array Arguments ..
   double precision,intent(inout) :: dx(*)
   ..

DEFINITION

 DSCAL scales a vector by a constant.
 uses unrolled loops for increment equal to 1.

OPTIONS

N number of elements in input vector(s) DA On entry, DA specifies the scalar alpha. DX array, dimension ( 1 + ( N - 1 )*abs( INCX ) ) INCX storage spacing between elements of DX

AUTHORS

  • Univ. of Tennessee
  • Univ. of California Berkeley
  • Univ. of Colorado Denver
  • NAG Ltd.

date:November 2017

FURTHER DETAILS

  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(*)

SEE ALSO

Online html documentation available at
http://www.netlib.org/lapack/explore-html/

Arguments

Type IntentOptional Attributes Name
integer, intent(in) :: n
double precision, intent(in) :: da
double precision, intent(inout) :: dx(*)
integer, intent(in) :: incx

Contents

Variables

Source Code

dscal

Variables

Type Visibility Attributes Name Initial
integer, public :: i
integer, public :: m
integer, public :: mp1
integer, public :: nincx

Source Code

       subroutine dscal(n,da,dx,incx)
      implicit none
!
!  -- Reference BLAS level1 routine (version 3.8.0) --
!  -- Reference BLAS is a software package provided by Univ. of Tennessee,    --
!  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
!     November 2017
!
!     .. Scalar Arguments ..
      double precision,intent(in)    :: da
      integer,intent(in)             :: incx,n
!     ..
!     .. Array Arguments ..
      double precision,intent(inout) :: dx(*)
!     ..
!  =====================================================================
!     .. Local Scalars ..
      integer i,m,mp1,nincx
!     ..
!     .. Intrinsic Functions ..
      intrinsic mod
!     ..
      if (n.le.0 .or. incx.le.0) return
      if (incx.eq.1) then
!
!        code for increment equal to 1
!
!
!        clean-up loop
!
         m = mod(n,5)
         if (m.ne.0) then
            do i = 1,m
               dx(i) = da*dx(i)
            enddo
            if (n.lt.5) return
         endif
         mp1 = m + 1
         do 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)
         enddo
      else
!
!        code for increment not equal to 1
!
         nincx = n*incx
         do i = 1,nincx,incx
            dx(i) = da*dx(i)
         enddo
      endif

      end subroutine dscal