stdlib_dsyr Subroutine

     pure subroutine stdlib_dsyr(uplo,n,alpha,x,incx,a,lda)
     !! DSYR performs the symmetric rank 1 operation
     !! A := alpha*x*x**T + A,
     !! where alpha is a real scalar, x is an n element vector and A is an
     !! n by n symmetric matrix.
        ! -- reference blas level2 routine --
        ! -- reference blas is a software package provided by univ. of tennessee,    --
        ! -- univ. of california berkeley, univ. of colorado denver and nag ltd..--
           ! Scalar Arguments 
           real(dp), intent(in) :: alpha
           integer(ilp), intent(in) :: incx, lda, n
           character, intent(in) :: uplo
           ! Array Arguments 
           real(dp), intent(inout) :: a(lda,*)
           real(dp), intent(in) :: x(*)
        ! =====================================================================
           
           ! Local Scalars 
           real(dp) :: temp
           integer(ilp) :: i, info, ix, j, jx, kx
           ! Intrinsic Functions 
           intrinsic :: max
           ! test the input parameters.
           info = 0
           if (.not.stdlib_lsame(uplo,'U') .and. .not.stdlib_lsame(uplo,'L')) then
               info = 1
           else if (n<0) then
               info = 2
           else if (incx==0) then
               info = 5
           else if (lda<max(1,n)) then
               info = 7
           end if
           if (info/=0) then
               call stdlib_xerbla('DSYR  ',info)
               return
           end if
           ! quick return if possible.
           if ((n==0) .or. (alpha==zero)) return
           ! set the start point in x if the increment is not unity.
           if (incx<=0) then
               kx = 1 - (n-1)*incx
           else if (incx/=1) then
               kx = 1
           end if
           ! start the operations. in this version the elements of a are
           ! accessed sequentially with one pass through the triangular part
           ! of a.
           if (stdlib_lsame(uplo,'U')) then
              ! form  a  when a is stored in upper triangle.
               if (incx==1) then
                   do j = 1,n
                       if (x(j)/=zero) then
                           temp = alpha*x(j)
                           do i = 1,j
                               a(i,j) = a(i,j) + x(i)*temp
                           end do
                       end if
                   end do
               else
                   jx = kx
                   do j = 1,n
                       if (x(jx)/=zero) then
                           temp = alpha*x(jx)
                           ix = kx
                           do i = 1,j
                               a(i,j) = a(i,j) + x(ix)*temp
                               ix = ix + incx
                           end do
                       end if
                       jx = jx + incx
                   end do
               end if
           else
              ! form  a  when a is stored in lower triangle.
               if (incx==1) then
                   do j = 1,n
                       if (x(j)/=zero) then
                           temp = alpha*x(j)
                           do i = j,n
                               a(i,j) = a(i,j) + x(i)*temp
                           end do
                       end if
                   end do
               else
                   jx = kx
                   do j = 1,n
                       if (x(jx)/=zero) then
                           temp = alpha*x(jx)
                           ix = jx
                           do i = j,n
                               a(i,j) = a(i,j) + x(ix)*temp
                               ix = ix + incx
                           end do
                       end if
                       jx = jx + incx
                   end do
               end if
           end if
           return
     end subroutine stdlib_dsyr