Packed storage with BLAS function

Question

I want to calculate A*x with A lower triangle matrix and x the vector. For example:

     1  0  0
A =  2  4  0
     3  5  6

with packed storage

 A = (/ 1, 2, 3, 4, 5, 6/) 

and

 X = (/1, 1, 1/)

Now I want to do A*x with BLAS function, shoud I tranform A back to be a 3x3 matrix? If not, could you please give me some hint? (I know in memory of fortran array, A is contiguously stored)

Answer 1

solved by checking: http://www.icl.utk.edu/~mgates3/docs/lapack.html

program main

  implicit none
  integer :: n
  real*8, allocatable, dimension(:) :: x
  real*8, allocatable, dimension(:) :: A

  n = 3
  allocate(A(n*(n+1)/2))
  allocate(x(n))
  A = 1.0d0
  x = 1.0d0

  ! x will be updated as A*x
  call dtpmv('L', 'N', 'N', n, A, x, 1)

  deallocate(A)
  deallocate(x)

end program main